Deficiency of MFSD7c results in microcephaly-associated vasculopathy in Fowler syndrome
Pazhanichamy Kalailingam, Kai Qi Wang, Xiu Ru Toh, Toan Q. Nguyen, Madhuvanthi Chandrakanthan, Zafrul Hasan, Clair Habib, Aharon Schif, Francesca Clementina Radio, Bruno Dallapiccola, Karin Weiss, Long N. Nguyen
Pazhanichamy Kalailingam, Kai Qi Wang, Xiu Ru Toh, Toan Q. Nguyen, Madhuvanthi Chandrakanthan, Zafrul Hasan, Clair Habib, Aharon Schif, Francesca Clementina Radio, Bruno Dallapiccola, Karin Weiss, Long N. Nguyen
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Research Article Vascular biology

Deficiency of MFSD7c results in microcephaly-associated vasculopathy in Fowler syndrome

Abstract

Several missense mutations in the orphan transporter FLVCR2 have been reported in Fowler syndrome. Affected subjects exhibit signs of severe neurological defects. We identified the mouse ortholog Mfsd7c as a gene expressed in the blood-brain barrier. Here, we report the characterizations of Mfsd7c-KO mice and compare these characterizations to phenotypic findings in humans with biallelic FLVCR2 mutations. Global KO of Mfsd7c in mice resulted in late-gestation lethality, likely due to CNS phenotypes. We found that the angiogenic growth of CNS blood vessels in the brain of Mfsd7c-KO embryos was inhibited in cortical ventricular zones and ganglionic eminences. Vascular tips were dilated and fused, resulting in glomeruloid vessels. Nonetheless, CNS blood vessels were intact, without hemorrhage. Both embryos and humans with biallelic FLVCR2 mutations exhibited reduced cerebral cortical layers, enlargement of the cerebral ventricles, and microcephaly. Transcriptomic analysis of Mfsd7cK-KO embryonic brains revealed upregulation of genes involved in glycolysis and angiogenesis. The Mfsd7c-KO brain exhibited hypoxia and neuronal cell death. Our results indicate that MFSD7c is required for the normal growth of CNS blood vessels and that ablation of this gene results in microcephaly-associated vasculopathy in mice and humans.

Authors

Pazhanichamy Kalailingam, Kai Qi Wang, Xiu Ru Toh, Toan Q. Nguyen, Madhuvanthi Chandrakanthan, Zafrul Hasan, Clair Habib, Aharon Schif, Francesca Clementina Radio, Bruno Dallapiccola, Karin Weiss, Long N. Nguyen

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Figure 1

MFSD7c is expressed in CNS blood vessels.

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MFSD7c is expressed in CNS blood vessels. (A) Immunostaining of MFSD7c w...
(A) Immunostaining of MFSD7c with polyclonal antibodies against murine MFSD7c in adult mouse brain. Expression of MFSD7c was found in CNS blood vessels, where it colocalized with GLUT1. Top, cortex; bottom, SVZ. Experiments were performed at least 4 times (n = 6). (B) Representative images of immunostaining of E18.5 WT and KO brain sections showing that MFSD7c was expressed in both apical and luminal side (indicated by arrows) of CNS endothelial cells. Asterisk shows erythrocytes, which were also positive with GLUT1 staining. Experiments were performed at least 4 times (n = 6 embryos per genotype). (C) MFSD7c is not expressed in pericytes. Immunostaining of E15.5 WT and KO brain sections with pericyte marker PDGFRb and MFSD7c. Arrowheads indicate pericytes. Experiments were performed at least 3 times (n = 3–4 embryos per genotype). (D) MFSD7c protein was detected in microvessel, but not parenchyma, fraction from WT adult brain. Protein lysates from E16.5 WT and KO embryos as well as MFSD7c protein expression in HEK293 cells were used to interpret the MFSD7c protein band. Note that the total amount of protein from HEK293 cells was 1 μg. Arrowheads show MFSD7c and GLUT1 protein bands. Experiments were performed 3 times.