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Posts Tagged ‘microcephaly’


Insight into Blood Brain Barrier

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

 

Gateway to The Brain

This image shows the structural model of critical transporter, Mfsd2a. Source: Duke-NUS Medical School
This image shows the structural model of critical transporter, Mfsd2a. Source: Duke-NUS Medical School.  http://www.dddmag.com/sites/dddmag.com/files/rd1604_brain.jpg

Scientists from Duke-NUS Medical School (Duke-NUS) have derived a structural model of a transporter at the blood-brain barrier called Mfsd2a. This is the first molecular model of this critical transporter, and could prove important for the development of therapeutic agents that need to be delivered to the brain — across the blood-brain barrier. In future, this could help treat neurological disorders such as glioblastoma.

Currently, there are limitations to drug delivery to the brain as it is tightly protected by the blood-brain barrier. The blood-brain barrier is a protective barrier that separates the circulating blood from the central nervous system which can prevent the entry of certain toxins and drugs to the brain. This restricts the treatment of many brain diseases. However, as a transporter at the blood-brain barrier, Mfsd2a is a potential conduit for drug delivery directly to the brain, thus bypassing the barrier.

In this study, recently published in the Journal of Biological Chemistry, first author Duke-NUS MD/PhD student Debra Quek and senior author Professor David Silver used molecular modeling and biochemical analyses of altered Mfsd2a transporters to derive a structural model of human Mfsd2a. Importantly, the work identifies new binding features of the transporter, providing insight into the transport mechanism of Mfsd2a.

“Our study provides the first glimpse into what Mfsd2a looks like and how it might transport essential lipids across the blood-brain barrier,” said Ms Quek. “It also facilitates a structure-guided search and design of scaffolds for drug delivery to the brain via Mfsd2a, or of drugs that can be directly transported by Mfsd2a.”

Currently this information is being used by Duke-NUS researchers to design novel therapeutic agents for direct drug delivery across the blood brain barrier for the treatment of neurological diseases. This initiative by the Centre for Technology and Development (CTeD) at Duke-NUS, is one of many collaborative research efforts aimed at translating Duke-NUS’ research findings into tangible commercial and therapeutic applications for patients.

Ms Quek plans to further validate her findings by purifying the Mfsd2a protein in order to further dissect how it functions as a transporter.

 

J Biol Chem. 2016 Mar 4. pii: jbc.M116.721035. [Epub ahead of print]
Structural insights into the transport mechanism of the human sodium-dependent lysophosphatidylcholine transporter Mfsd2a.

Major Facilitator Superfamily Domain containing 2A (Mfsd2a) was recently characterized as a sodium-dependent lysophosphatidylcholine (LPC) transporter expressed at the blood-brain barrier endothelium. It is the primary route for importation of docosohexaenoic acid and other long-chain fatty acids into foetal and adult brain, and is essential for mouse and human brain growth and function. Remarkably, Mfsd2a is the first identified MFS family member that uniquely transports lipids, implying that Mfsd2a harbours unique structural features and transport mechanism. Here, we present three 3D structural models of human Mfsd2a derived by homology modelling using MelB- and LacY-based crystal structures, and refined by biochemical analysis. All models revealed 12 transmembrane helices and connecting loops, and represented the partially outward-open, outward-partially occluded, and inward-open states of the transport cycle. In addition to a conserved sodium-binding site, three unique structural features were identified: A phosphate headgroup binding site, a hydrophobic cleft to accommodate a hydrophobic hydrocarbon tail, and three sets of ionic locks that stabilize the outward-open conformation. Ligand docking studies and biochemical assays identified Lys436 as a key residue for transport. It is seen forming a salt bridge with the negative charge on the phosphate headgroup. Importantly, Mfsd2a transported structurally related acylcarnitines but not a lysolipid without a negative charge, demonstrating the necessity of a negative charged headgroup interaction with Lys436 for transport. These findings support a novel transport mechanism by which LPCs are flipped within the transporter cavity by pivoting about Lys436 leading to net transport from the outer to the inner leaflet of the plasma membrane.

 

Brain and eye contain membrane phospholipids that are enriched in the omega-3 fatty acid docosohexaenoic acid (DHA). It is widely accepted that DHA is important for brain and eye function and brain development (1,2), although mechanisms for DHA function in these tissues are not well defined.   The mechanism by which DHA and other conditionally essential and essential fatty acids cross the blood-brain barrier (BBB) has been a long-standing mystery. Recently, we identified Major Facilitator Superfamily Domain containing 2a (Mfsd2a, aka NLS1) as the primary transporter by which the brain obtains DHA. Importantly, Mfsd2a does not transport unesterified DHA, but transports DHA in the chemical form of lysophosphatidylcholine (LPC) that are synthesized by the liver and circulate largely on albumin (3). This is consistent with biochemical evidence that the brain does not transport unesterified fatty acids (4) and that LPC is the preferred carrier of DHA to the brain (5,6).   Mfsd2a is a sodium-dependent transporter that is part of the Major Facilitator Superfamily (MFS) of proteins. Members of this family with elucidated structures have 12 transmembrane domains composed of two evolutionarily duplicated 6 transmembrane units (7). Transporting an LPC is a unique feature of Mfsd2a, since most members of this family transport water-soluble and minimally polar substrates such as sugars (GLUT, MelB, LacY), and amino acids (TAT1). Mfsd2a transport is not limited to LPCs containing DHA, as it can transport LPCs containing a variety of fatty acyl chains, with higher specificity for LPCs with unsaturated fatty acyl chains with a minimum chain length of 14 carbons (6,8). Crystal structures have been solved for more than a dozen members of the MFS family, with more than 19 structures, including that of Melibiose permease (MelB) of S. typhimurium (9), Lactose permease (LacY) of Escherichia coli (10), glycerol-3-phosphate transporter of E. coli (11) and the mammalian glucose transporters 1, 3, and 5 (GLUT1, GLUT3, GLUT5) (12-14). A common transport mechanism has emerged from both biochemical and structural analyses of MFSs, in which they transport via a rocker-switch, alternating access mechanism (7,15). In the rocker-switch model, rigid-body relative motion of the N- and C-termini domains renders the substrate-binding site alternatively accessible from either side of the membrane.

Mfsd2a is highly expressed at the bloodbrain barrier in both mouse and human (6,16). Mfsd2a deficient mice (KO) have significantly reduced brain DHA as a result of a 90% reduction in brain uptake of LPC containing DHA as well as other LPCs. The most prominent phenotype of Mfsd2a KO mice is microcephaly, and KO mice additionally exhibit motor dysfunction, and behavioral disorders including anxiety and memory and learning deficits (6). In line with the mouse KO phenotypes, human patients with partially or completely inactivating mutations in Mfsd2a presented with severe microcephaly, intellectual disability, and motor dysfunction (8,16). Plasma LPCs are significantly elevated in both KO mice and human patients with Mfsd2a mutations, consistent with reduced uptake at the blood-brain barrier. Taken together, these findings demonstrate that LPCs are essential for normal brain development and function in mouse and humans.

The fact that Mfsd2a transports a lysolipid, a non-canonical substrate for an MFS protein, might indicate unique structure features and a novel transport mechanism. However, no structural information or mechanism of transport of Mfsd2a is known. Human Mfsd2a is composed of 530 amino acids, with two glycosylation sites at Asn217 and Asn227. Mfsd2a is evolutionarily conserved from teleost fish to humans. Although not a functional ortholog of bacterial MFS transporters, Mfsd2a shares 25% and 26% amino acid sequence identity with S. typhimurium MelB (9,17), and LacY from E. coli (10), respectively. Given the high conservation of the MFS fold, the use of homology modeling to gain insight into the structure of S. typhimurium MelB, for example, has proven to be highly accurate and largely consistent with subsequent X-ray crystal data (9,18). Here, we take advantage of two recently derived high resolution X-ray crystal structures of S. typhimurium MelB (9), and a high resolution X-ray crystal structure of LacY (10) to generate three predictive structural models of human Mfsd2a. These models reveal three unique regions critical for function – an LPC headgroup binding site, a hydrophobic cleft occupied by the LPC fatty acyl tail, and three sets of ionic locks. These structural features indicate a novel mechanism of transport for LPCs.

Mfsd2a is a sodium-dependent lysophosphatidylcholine transporter essential for human brain growth and function (40). Mfsd2a is the only known MFS member or secondary transporter that transports a lipid. In line with its unique function, the current study has identified three unique structural features based on a combination of homology structural modeling and biochemical analysis – (1) a unique headgroup binding site and (2) a hydrophobic cleft for acyl chain binding, and (4) 3 sets of ionic locks that stabilize the outward open conformation. Drawing together these findings with studies of the mechanism of transport of other MFS family members, we propose the following alternatingaccess mechanism for LPC transport (Fig. 6). In the first steps, LPC inserts itself into the outer leaflet of the membrane and diffuses laterally into the transporter’s hydrophobic cleft. As Mfsd2a undergoes conformational changes from the outward open to the inward open conformation, the zwitterionic headgroup is inverted from the outer membrane leaflet to the inner membrane leaflet along a translocation pathway within the transporter, interacting with specific polar and charged residues lining the path. Since LPCs are hydrophobic phospholipids, it is unlikely that they will partition out of the transporter into the aqueous environment of the cytoplasm. We propose that the “flipped” LPC exits the transporter laterally into the membrane environment of the inner leaflet. This model of LPC flipping requires further biochemical proof. Of particular interest is the visualization of the interaction of the negatively charged phosphate headgroup of LPC with Lys436 that is maintained in both outward and inward open conformations. The sidechain of Lys436 is seen to be pointing in the upward direction in the outward open conformation, but pointing downward into the translocation cleft in the inward open conformation. These findings suggest that the Lys436 acts as a tether to push or pivot the headgroup down into the translocation cavity while the N- and C-termini of Mfsd2a rock and switch from outward to inward open.

Interestingly, Lys436 is orthologous to the residue Lys377 in the melibiose transporter of S. typhimurium. Based on the S. typhimurium MelB crystal structure, Lys377 has been predicted to be involved in binding melibiose, and in forming a hydrogen bond with Tyr120, likely separating the sodium binding site from the central hydrophilic cavity (9). In a recent molecular dynamic simulation of E. coli MelB, Lys377 was noted to interact differently with residues involved in the sodium binding site (Asp55, Asp59, and Asp124) in the presence or absence of a sodium ion, and thought to be critical for the spatial organization of the sodium binding site (41). Similarly, in our refined models of Mfsd2a, Lys436 is localized in close proximity to the sodium-binding site residue, Asp93, and the central translocation pathway where it has been identified by docking studies to interact with the charged headgroup of LPC. We hypothesize that Lys436 may shuttle between the two binding sites, communicating and coordinating the occupancy status of the two sites. Interestingly, there is a distinct mobility shift in Mfsd2a bands on SDS-PAGE between wild-type Mfsd2a and the L-3 mutant (R498E, R499E, R500E, K503E, K504E) (Fig. 5I) that is not seen when each of the residues are mutated individually (Fig. S1). These findings are consistent with a conformational change in the L-3 mutant. Given that the L-3 ionic lock is visualized in the outward partially occluded model, we hypothesize that the loss of the L-3 ionic lock results in Mfsd2a being trapped in an energetically more favorable inward open conformation, resulting in the loss of transport function (Fig. 5H).

Patients with the partially inactivating mutation p.(S399L) exhibited significant increases specifically in plasma LPCs having monounsaturated (18:1 – 92%, p=0.004) and polyunsaturated LPCs (18:2, 20:4, 20:3 – 254%, p=0.002; 117%, p=0.007, and 238%, p=0.002), but not in the most abundant LPCs – saturated LPCs (C16:0, C18:0) (8). This is consistent with a greater specificity of Mfsd2a for LPCs with unsaturated fatty acyl chains (6)…A possible explanation for this acyl chain specificity is related to the mobility of the acyl tail in the membrane. It is known that phospholipids with unsaturated fatty acyl chains disrupt the packing of the bilayer, resulting in greater lateral membrane fluidity (42). Therefore, one possible mechanism for LPC specificity is that LPCs with unsaturated fatty acyl chains have greater lateral mobility in the membrane, increasing the Ka for interacting with the transport cleft of Mfsd2a.

Another important structural feature of the physiological ligand, LPC, is a minimum acyl chain length of 14 carbons is required for transport by Mfsd2a. A possible explanation for this requirement is that the hydrocarbon chain must extend beyond the cleft, protruding into the hydrophobic milieu of the phospholipid bilayer core. This interaction of the fatty acyl tail with the acyl chains of the membrane bilayer may provide a hydrophobic force strong enough to pull the molecule through and out of the transporter as the LPC headgroup partitions into the inner leaflet of the membrane. A similar scenario is seen in the Sec translocon where a hydrophobic transmembrane domain of a protein partitions laterally from the Sec61p complex channel into the lipid bilayer (43,44). This proposal that the omega carbon of the fatty acyl chain sticks out of the Mfsd2a pocket is consistent with the observation that Mfsd2a can transport nitrobenzoxadiazole (NBD) or Topfluor when these moieties are attached to the omega carbon of the LPC fatty acyl tail [1].

Other known transmembrane phospholipid transporters include flippases, floppases, and scramblases. Flippases and floppases utilize ATP to drive the uphill transport of aminophospholipids from the outer to the inner leaflet, and specific substrates from the inner to the outer leaflet, respectively (45-47). Scramblases are less well understood, facilitating transport of substrates in either direction down concentration gradients upon activation. While the substrates are similar, several differences make comparisons between Mfsd2a and phospholipid transporters of limited relevance. First, the shapes of the substrates differ in shape and size – lysophospholipids are smaller and conical while phospholipids are cylindrical. Second, unlike flippases and floppases, Mfsd2a is a secondary transporter, utilizing a sodium electrochemical gradient to drive the transport of lysophospholipids from one leaflet to the other. Third, the overall structure of MFS members is different from P4- ATPases and ABC transporters. Consequently, the mechanism of action between Mfsd2a and flippases such as P4-ATPases and ABC transporters, or floppases is expected to differ.

Being expressed at the blood-brain barrier, Mfsd2a is a potential conduit for drug delivery to the brain. The blood-brain barrier is highly impermeable, protecting the brain from bloodderived molecules, pathogens, and toxins. However, its impermeability poses a challenge for pharmacological treatment of brain diseases. It has been predicted that 98% of small molecule drugs are excluded from the brain by the blood-brain barrier (48). Currently, most drugs used to treat brain diseases are lipid soluble small molecules with a molecular weight of less than 400 Da (49). A small number of drugs traverse the blood-brain barrier by carrier-mediated transport. An example of this is Levodopa, a treatment for Parkinson’s Disease, which is a precursor of the neurotransmitter dopamine. Levodopa is transported across the blood-brain barrier by the large neutral amino acid transporter, LAT1 (50). Our findings here provide a further refinement of understanding of the structure-activity relationship of LPCs to their transport, and educates the search and design of drugs that can be transported by Mfsd2a. Candidates for transport, whether as a drug itself or as a LPC scaffold, must have a zwitterionic headgroup, but not necessarily a phosphate, and a minimal threshold of hydrophobic character. As the binding pocket is several times larger than LPC, it is sterically feasible to attach a small molecule drug onto LPC or LPC-like scaffolds for delivery across the blood-brain barrier.

In summary, these studies represent a first structural model of human Mfsd2a based on homology modeling and biochemical interrogation. We expect that this model will serve as a foundation for the future development of X-ray crystal structures of the protein, which would provide further insight into the structure and function of this physiologically important transporter required for human brain growth and function.

REFERENCES

1. Salem, N., Jr., Litman, B., Kim, H. Y., and Gawrisch, K. (2001) Mechanisms of action of docosahexaenoic acid in the nervous system. Lipids 36, 945-959

2. Bazan, N. G. (2009) Neuroprotectin D1-mediated anti-inflammatory and survival signaling in stroke, retinal degenerations, and Alzheimer’s disease. Journal of lipid research 50 Suppl, S400- 405

3. Baisted, D. J., Robinson, B. S., and Vance, D. E. (1988) Albumin stimulates the release of lysophosphatidylcholine from cultured rat hepatocytes. The Biochemical journal 253, 693-701

4. Edmond, J., Higa, T. A., Korsak, R. A., Bergner, E. A., and Lee, W. N. (1998) Fatty acid transport and utilization for the developing brain. Journal of neurochemistry 70, 1227-1234

5. Lagarde, M., Bernoud, N., Brossard, N., Lemaitre-Delaunay, D., Thies, F., Croset, M., and Lecerf, J. (2001) Lysophosphatidylcholine as a preferred carrier form of docosahexaenoic acid to the brain. Journal of molecular neuroscience : MN 16, 201-204; discussion 215-221

6. Nguyen, L. N., Ma, D., Shui, G., Wong, P., Cazenave-Gassiot, A., Zhang, X., Wenk, M. R., Goh, E. L., and Silver, D. L. (2014) Mfsd2a is a transporter for the essential omega-3 fatty acid docosahexaenoic acid. Nature 509, 503-506

7. Law, C. J., Maloney, P. C., and Wang, D. N. (2008) Ins and outs of major facilitator superfamily antiporters. Annual review of microbiology 62, 289-305

8. Alakbarzade, V., Hameed, A., Quek, D. Q. Y., Chioza, B. A., Baple, E. L., Cazenave-Gassiot, A., Nguyen, L. N., Wenk, M. R., Ahmad, A. Q., Sreekantan-Nair, A., Weedon, M. N., Rich, P., Patton, M. A., Warner, T. T., Silver, D. L., and Crosby, A. H. (2015) A partially inactivating mutation in the sodium-dependent lysophosphatidylcholine transporter MFSD2A causes a non-lethal microcephaly syndrome. Nat Genet 47, 814-817

9. Ethayathulla, A. S., Yousef, M. S., Amin, A., Leblanc, G., Kaback, H. R., and Guan, L. (2014) Structure-based mechanism for Na(+)/melibiose symport by MelB. Nature communications 5, 3009

10. Guan, L., Mirza, O., Verner, G., Iwata, S., and Kaback, H. R. (2007) Structural determination of wild-type lactose permease. Proceedings of the National Academy of Sciences of the United States of America 104, 15294-15298

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Zika and neurone disorder

Larry H. Bernstein, MD, FCAP, Curator

LPBI

Zika virus impairs growth in human neurospheres and brain organoids

Since the emergence of Zika virus (ZIKV), reports of microcephaly have increased significantly in Brazil; however, causality between the viral epidemic and malformations in fetal brains needs further confirmation. Here, we examine the effects of ZIKV infection in human neural stem cells growing as neurospheres and brain organoids. Using immunocytochemistry and electron microscopy, we show that ZIKV targets human brain cells, reducing their viability and growth as neurospheres and brain organoids. These results suggest that ZIKV abrogates neurogenesis during human brain development.

Primary microcephaly is a severe brain malformation characterized by the reduction of the head circumference. Patients display a heterogeneous range of brain impairments, compromising motor, visual, hearing and cognitive functions (1).

Microcephaly is associated with decreased neuronal production as a consequence of proliferative defects and death of cortical progenitor cells (2). During pregnancy, the primary etiology of microcephaly varies from genetic mutations to external insults. The so-called TORCHS factors (Toxoplasmosis, Rubella, Cytomegalovirus, Herpes virus, Syphilis) are the main congenital infections that compromise brain development in utero (3).

The increase in the rate of microcephaly in Brazil has been associated with the recent outbreak of Zika virus (ZIKV) (4, 5), a flavivirus that is transmitted by mosquitoes (6) and sexually (79). So far, ZIKV has been described in the placenta and amniotic fluid of microcephalic fetuses (1013), and in the blood of microcephalic newborns (11, 14). ZIKV had also been detected within the brain of a microcephalic fetus (13, 14), and recently, there is direct evidence that ZIKV is able to infect and cause death of neural stem cells (15).

Here, we used human induced pluripotent stem (iPS) cells cultured as neural stem cells (NSC), neurospheres and brain organoids to explore the consequences of ZIKV infection during neurogenesis and growth with 3D culture models. Human iPS-derived NSCs were exposed to ZIKV (MOI 0.25 to 0.0025). After 24 hours, ZIKV was detected in NSCs (Fig. 1, A to D), when viral envelope protein was shown in 10.10% (MOI 0.025) and 21.7% (MOI 0.25) of cells exposed to ZIKV (Fig. 1E). Viral RNA was also detected in the supernatant of infected NSCs (MOI 0.0025) by qRT-PCR (Fig. 1F), supporting productive infection.

Fig. 1ZIKV infects human neural stem cells.

Confocal microscopy images of iPS-derived NSCs double stained for (A) ZIKV in the cytoplasm, and (B) SOX2 in nuclei, one day after virus infection. (C) DAPI staining, (D) merged channels show perinuclear localization of ZIKV. Bar = 100 μm. (E) Percentage of ZIKV infected SOX2 positive cells (MOI 0.25 and 0.025). (F) RT-PCR analysis of ZIKV RNA extracted from supernatants of mock and ZIKV-infected neurospheres (MOI 0.0025) after 3 DIV, showing amplification only in infected cells. RNA was extracted, qPCR performed and virus production normalized to 12h post-infection controls. Data presented as mean ± SEM, n=5, Student’s t test, *p < 0.05, **p < 0.01.

To investigate the effects of ZIKV during neural differentiation, mock- and ZIKV-infected NSCs were cultured as neurospheres. After 3 days in vitro, mock NSCs generated round neurospheres. However, ZIKV-infected NSCs generated neurospheres with morphological abnormalities and cell detachment (Fig. 2B). After 6 days in vitro (DIV), hundreds of neurospheres grew under mock conditions (Fig. 2, C and E). Strikingly, in ZIKV-infected NSCs (MOI 2.5 to 0.025) only a few neurospheres survived (Fig. 2, D and E).

Fig. 2ZIKV alters morphology and halts the growth of human neurospheres.

(A) Control neurosphere displays spherical morphology after 3 DIV. (B) Infected neurosphere showed morphological abnormalities and cell detachment after 3 DIV. (C) Culture well-plate containing hundreds of mock neurospheres after 6 DIV. (D) ZIKV-infected well-plate (MOI 2.5-0.025) containing few neurospheres after 6 DIV. Bar = 250 μm in (A) and (B), and 1 cm in (C) and (D). (E) Quantification of the number of neurospheres in different MOI. Data presented as mean ± SEM, n=3, Student’s t test, ***p < 0.01.

Mock neurospheres presented expected ultrastructural morphology of nucleus and mitochondria (Fig. 3A). ZIKV-infected neurospheres revealed the presence of viral particles, similarly to those observed in murine glial and neuronal cells (16). ZIKV was bound to the membranes and observed in mitochondria and vesicles of cells within infected neurospheres (Fig. 3, B and F, arrows). Apoptotic nuclei, a hallmark of cell death, were observed in all ZIKV-infected neurospheres analyzed (Fig. 3B). Of note, ZIKV-infected cells in neurospheres presented smooth membrane structures (SMS) (Fig. 3, B and F), similarly to those previously described in other cell types infected with dengue virus (17). These results suggest that ZIKV induces cell death in human neural stem cells and thus impairs the formation of neurospheres.

Fig. 3ZIKV induces death in human neurospheres.

Ultrastructure of mock- and ZIKV-infected neurospheres after 6 days in vitro. (A) Mock-infected neurosphere showing cell processes and organelles, (B) ZIKV-infected neurosphere shows pyknotic nucleus, swollen mitochondria, smooth membrane structures and viral envelopes (arrow). Arrows point viral envelopes on cell surface (C), inside mitochondria (D), endoplasmic reticulum (E) and close to smooth membrane structures (F). Bar = 1 μm in (A) and (B) and 0.2 μm in (C) to (F). m = mitochondria; n = nucleus; sms = smooth membrane structures.

To further investigate the impact of ZIKV infection during neurogenesis, human iPS-derived brain organoids (18) were exposed with ZIKV, and followed for 11 days in vitro (Fig. 4). The growth rate of 12 individual organoids (6 per condition) was measured during this period (Fig. 4, A and D). As a result of ZIKV infection, the average growth area of ZIKV-exposed organoids was reduced by 40% when compared to brain organoids under mock conditions (0.624 mm2 ± 0.064 ZIKV-exposed organoids versus 1.051 mm2 ± 0.1084 mock-infected organoids normalized, Fig. 4E).

Fig. 4ZIKV reduces the growth rate of human brain organoids.

35 days old brain organoids were infected with (A) MOCK and (B) ZIKV for 11 days in vitro. ZIKV-infected brain organoids show reduction in growth compared with MOCK. Arrows point to detached cells. Organoid area was measured before and after 11 days exposure with (C) MOCK and (D) ZIKV in vitro. Plotted quantification represent the growth rate. (E) Quantification of the average of mock- and ZIKV-infected organoid area 11 days after infection in vitro. Data presented as mean ± SEM, n=6, Student’s ttest, *p < 0.05.

In addition to MOCK infection, we used dengue virus 2 (DENV2), a flavivirus with genetic similarities to ZIKV (11, 19), as an additional control group. One day after viral exposure, DENV2 infected human NSCs with a similar rate as ZIKV (fig. S1, A and B). However, after 3 days in vitro, there was no increase in caspase 3/7 mediated cell death induced by DENV2 with the same 0.025 MOI adopted for ZIKV infection (fig. S1, C and D). On the other hand, ZIKV induced caspase 3/7 mediated cell death in NSCs, similarly to the results described by Tang and colleagues (15). After 6 days in vitro, there is a significant difference in cell viability between ZIKV-exposed NSCs compared to DENV2-exposed NSCs (fig. S1, E and F). In addition, neurospheres exposed to DENV2 display a round morphology such as uninfected neurospheres after 6 days in vitro (fig. S1G). Finally, there was no reduction of growth in brain organoids exposed to DENV2 for 11 days compared to MOCK (1.023 mm2 ± 0.1308 DENV2-infected organoids versus 1.011 mm2 ± 0.2471 mock-infected organoids normalized, fig. S1, H and I). These results suggest that the deleterious consequences of ZIKV infection in human NSCs, neurospheres and brain organoids are not a general feature of the flavivirus family. Neurospheres and brain organoids are complementary models to study embryonic brain development in vitro (20, 21). While neurospheres present the very early characteristics of neurogenesis, brain organoids recapitulate the orchestrated cellular and molecular early events comparable to the first trimester fetal neocortex, including gene expression and cortical layering (18, 22). Our results demonstrate that ZIKV induces cell death in human iPS-derived neural stem cells, disrupts the formation of neurospheres and reduces the growth of organoids (fig. S2), indicating that ZIKV infection in models that mimics the first trimester of brain development may result in severe damage. Other studies are necessary to further characterize the consequences of ZIKV infection during different stages of fetal development.

Cell death impairing brain enlargement, calcification and microcephaly is well described in congenital infections with TORCHS (3, 23, 24). Our results, together with recent reports showing brain calcification in microcephalic fetuses and newborns infected with ZIKV (10, 14) reinforce the growing body of evidence connecting congenital ZIKV outbreak to the increased number of reports of brain malformations in Brazil.

Supplementary Materials

www.sciencemag.org/cgi/content/full/science.aaf6116/DC1

Materials and Methods

Figs. S1 and S2

References (2527)

 

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http://science.sciencemag.org/content/early/2016/04/08/science.aaf6116.full

 

Zika Virus Tied to MS-Like Brain Disorder

http://www.genengnews.com/gen-news-highlights/zika-virus-tied-to-ms-like-brain-disorder/81252591/

Scientists report that the Zika virus may be associated with an autoimmune disorder that attacks the brain’s myelin similar to multiple sclerosis (MS). The investigators will discuss the results of their research at the upcoming American Academy of Neurology’s 68th Annual Meeting in Vancouver, Canada.

“Though our study is small, it may provide evidence that in this case the virus has different effects on the brain than those identified in current studies,” said study author Maria Lucia Brito Ferreira, M.D., with Restoration Hospital in Recife, Brazil. “Much more research will need to be done to explore whether there is a causal link between Zika and these brain problems.”

For the study, researchers followed people who came to the hospital in Recife from December 2014 to June 2015 with symptoms compatible with arboviruses, the family of viruses that includes Zika, dengue, and chikungunya. Six people then developed neurologic symptoms that were consistent with autoimmune disorders and underwent exams and blood tests. The authors saw 151 cases with neurological manifestations during a period of December 2014 to December 2015.

All of the people came to the hospital with fever followed by a rash. Some also had severe itching, muscle and joint pain, and red eyes. The neurologic symptoms started right away for some people and up to 15 days later for others.

Of the six people who had neurologic problems, two of the people developed acute disseminated encephalomyelitis (ADEM), a swelling of the brain and spinal cord that attacks the myelin. In both cases, brain scans showed signs of damage to the brain’s white matter. Unlike MS, ADEM usually consists of a single attack that most people recover from within 6 months. In some cases, the disease can reoccur. Four of the people developed Guillain-Barré syndrome (GBS), a syndrome that involves myelin of the peripheral nervous system and has a previously reported association with the Zika virus.

When they were discharged from the hospital, five of the six people still had problems with motor functioning. One person had vision problems and one had problems with memory and thinking skills. Tests showed that the participants all had Zika virus. Tests for dengue and chikungunya were negative.

“This doesn’t mean that all people infected with Zika will experience these brain problems. Of those who have nervous system problems, most do not have brain symptoms,” said Dr. Ferreira. “However, our study may shed light on possible lingering effects the virus may be associated with in the brain.”

“At present, it does not seem that ADEM cases are occurring at a similarly high incidence as the GBS cases, but these findings from Brazil suggest that clinicians should be vigilant for the possible occurrence of ADEM and other immune-mediated illnesses of the central nervous system,” noted James Sejvar, M.D., with the Centers for Disease Control and Prevention in Atlanta and a member of the American Academy of Neurology. “Of course, the remaining question is ‘why’—why does Zika virus appear to have this strong association with GBS and potentially other immune/inflammatory diseases of the nervous system? Hopefully, ongoing investigations of Zika virus and immune-mediated neurologic disease will shed additional light on this important question.”

Zika Virus Structure Revealed

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Team at Purdue becomes the first to determine the structure of the Zika virus, which reveals insights critical to the development of effective antiviral treatments and vaccines.

The team also identified regions within the Zika virus structure where it differs from other flaviviruses, the family of viruses to which Zika belongs that includes dengue, West Nile, yellow fever, Japanese encephalitis and tick-borne encephalitic viruses.

Any regions within the virus structure unique to Zika have the potential to explain differences in how a virus is transmitted and how it manifests as a disease, said Richard Kuhn, director of the Purdue Institute for Inflammation, Immunology and Infectious Diseases (PI4D) who led the research team with Michael Rossmann, Purdue’s Hanley Distinguished Professor of Biological Sciences.

“The structure of the virus provides a map that shows potential regions of the virus that could be targeted by a therapeutic treatment, used to create an effective vaccine or to improve our ability to diagnose and distinguish Zika infection from that of other related viruses,” said Kuhn, who also is head of Purdue’s Department of Biological Sciences. “Determining the structure greatly advances our understanding of Zika – a virus about which little is known. It illuminates the most promising areas for further testing and research to combat infection.”

The Zika virus, a mosquito-borne disease, has recently been associated with a birth defect called microcephaly that causes brain damage and an abnormally small head in babies born to mothers infected during pregnancy. It also has been associated with the autoimmune disease Guillain-Barré syndrome, which can lead to temporary paralysis. In the majority of infected individuals symptoms are mild and include fever, skin rashes and flulike illness, according to the World Health Organization.

Zika virus transmission has been reported in 33 countries. Of the countries where Zika virus is circulating 12 have reported an increased incidence of Guillain-Barré syndrome, and Brazil and French Polynesia have reported an increase in microcephaly, according to WHO. In February WHO declared the Zika virus to be “a public health emergency of international concern.”

“This breakthrough illustrates not only the importance of basic research to the betterment of human health, but also its nimbleness in quickly addressing a pressing global concern,” said Purdue President Mitch Daniels. “This talented team of researchers solved a very difficult puzzle in a remarkably short period of time, and have provided those working on developing vaccines and treatments to stop this virus a map to guide their way.”

Rossmann and Kuhn collaborated with Theodore Pierson, chief of the viral pathogenesis section of the Laboratory of Viral Diseases at the National Institutes of Health National Institute of Allergy and Infectious Diseases. Additional research team members include Purdue graduate student Devika Sirohi and postdoctoral research associates Zhenguo Chen, Lei Sun and Thomas Klose.

The team’s paper marks the first published success of the new Purdue Institute for Inflammation, Immunology and Infectious Diseases in Purdue’s Discovery Park.

The university’s recently announced $250 million investment in the life sciences funded the purchase of advanced equipment that allowed the team to do in a couple of months what otherwise would have taken years, Rossmann said.

“We were able to determine through cryo-electron microscopy the virus structure at a resolution that previously would only have been possible through X-ray crystallography,” he said. “Since the 1950s X-ray crystallography has been the standard method for determining the structure of viruses, but it requires a relatively large amount of virus, which isn’t always available; it can be very difficult to do, especially for viruses like Zika that have a lipid membrane and don’t organize accurately in a crystal; and it takes a long time. Now, we can do it through electron microscopy and view the virus in a more native state. This was unthinkable only a few years ago.”

The team studied a strain of Zika virus isolated from a patient infected during the French Polynesia epidemic and determined the structure to 3.8Å. At this near-atomic resolution key features of the virus structure can be seen and groups of atoms that form specific chemical entities, such as those that represent one of 20 naturally occurring amino acids, can be recognized, Rossmann said.

The team found the structure to be very similar to that of other flaviviruses with an RNA genome surrounded by a lipid, or fatty, membrane inside an icosahedral protein shell.

The strong similarity with other flaviviruses was not surprising and is perhaps reassuring in terms of vaccine development already underway, but the subtle structural differences are possibly key, Sirohi said.

“Most viruses don’t invade the nervous system or the developing fetus due to blood-brain and placental barriers, but the association with improper brain development in fetuses suggest Zika does,” Sirohi said. “It is not clear how Zika gains access to these cells and infects them, but these areas of structural difference may be involved. These unique areas may be crucial and warrant further investigation.”

The team found that all of the known flavivirus structures differ in the amino acids that surround a glycosylation site in the virus shell. The shell is made up of 180 copies of two different proteins. These, like all proteins, are long chains of amino acids folded into particular structures to create a protein molecule, Rossmann said.

The glycosylation site where Zika virus differs from other flaviviruses protrudes from the surface of the virus. A carbohydrate molecule consisting of various sugars is attached to the viral protein surface at this site.

In many other viruses it has been shown that as the virus projects a glycosylation site outward, an attachment receptor molecule on the surface of a human cell recognizes the sugars and binds to them, Kuhn said.

The virus is like a menacing stranger luring an unsuspecting victim with the offer of sweet candy. The human cell gladly reaches out for the treat and then is caught by the virus, which, once attached, may initiate infection of that cell.

The glycosylation site and surrounding residues on Zika virus may also be involved in attachment to human cells, and the differences in the amino acids between different flaviviruses could signify differences in the kinds of molecules to which the virus can attach and the different human cells it can infect, Rossmann said.

“If this site functions as it does in dengue and is involved in attachment to human cells, it could be a good spot to target an antiviral compound,” Rossmann said. “If this is the case, perhaps an inhibitor could be designed to block this function and keep the virus from attaching to and infecting human cells.”

The team plans to pursue further testing to evaluate the different regions as targets for treatment and to develop potential therapeutic molecules, Kuhn said.

Kuhn and Rossmann have studied flaviviruses, the family of viruses to which Zika belongs, for more than 14 years. They were the first to map the structure of any flavivirus when they determined the dengue virus structure in 2002. In 2003 they were first to determine the structure of West Nile virus and now they are the first to do so with the Zika virus.

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