Profiling of Sexually Dimorphic Genes in Neural Cells to Identify Eif2s3y, Whose Overexpression Causes Autism-Like Behaviors in Male Mice.

Many neurological disorders exhibit sex differences and sex-specific therapeutic responses. Unfortunately, significant amounts of studies investigating molecular and cellular mechanisms underlying these neurological disorders use primary cell cultures with undetermined sexes; and this may be a source for contradictory results among different studies and impair the validity of study conclusion. Herein, we comprehensively compared sexual dimorphism of gene expression in primary neurons, astrocytes, and microglia derived from neonatal mouse brains. We found that overall sexually dimorphic gene numbers were relatively low in these primary cells, with microglia possessing the most (264 genes), neurons possessing the medium (69 genes), and astrocytes possessing the least (30 genes). KEGG analysis indicated that sexually dimorphic genes in these three cell types were strongly enriched for the immune system and immune-related diseases. Furthermore, we identified that sexually dimorphic genes shared by these primary cells dominantly located on the Y chromosome, including Ddx3y, Eif2s3y, Kdm5d, and Uty. Finally, we demonstrated that overexpression of Eif2s3y increased synaptic transmission specifically in male neurons and caused autism-like behaviors specifically in male mice. Together, our results demonstrate that the sex of primary cells should be considered when these cells are used for studying the molecular mechanism underlying neurological disorders with sex-biased susceptibility, especially those related to immune dysfunction. Moreover, our findings indicate that dysregulation of sexually dimorphic genes on the Y chromosome may also result in autism and possibly other neurological disorders, providing new insights into the genetic driver of sex differences in neurological disorders.

TMEM59 interacts with TREM2 and modulates TREM2-dependent microglial activities.

The surface receptor triggering receptor expressed on myeloid cells 2 (TREM2) plays a crucial role in maintaining a multitude of microglial activities, such as survival, proliferation, migration, metabolism, inflammation, and phagocytosis. However, the molecular mechanisms underlying TREM2-mediated microglial activities remain largely elusive. Herein, we found that TREM2 interacted with the type I transmembrane protein TMEM59, whose expression could facilitate autophagic flux through its carboxyl-terminus. TMEM59 expression was decreased upon lipopolysaccharide treatment. While downregulation of TMEM59 promoted anti-inflammatory factor expression and attenuated lipopolysaccharide treatment-induced inflammation. Importantly, we found that overexpression of TREM2 reduced TMEM59 protein levels through promoting its degradation, whereas TMEM59 levels were elevated in Trem2-deficient microglia. Finally, impaired survival, proliferation, migration, and phagocytosis, as well as dysregulated autophagy and metabolism in Trem2-deficient microglia were attenuated upon TMEM59 silencing. Together, our findings reveal a novel function of TREM2 in mediating TMEM59 protein degradation and demonstrate the importance of TMEM59 homeostasis in maintaining TREM2-mediated microglial activities.

A brain somatic RHEB doublet mutation causes focal cortical dysplasia type II.

Focal cortical dysplasia type II (FCDII) is a cerebral cortex malformation characterized by local cortical structure disorganization, neuronal dysmorphology, and refractory epilepsy. Brain somatic mutations in several genes involved in the PI3K/AKT/mTOR pathway are associated with FCDII, but they are only found in a proportion of patients with FCDII. The genetic causes underlying the development FCDII in other patients remain unclear. Here, we carried out whole exome sequencing and targeted sequencing in paired brain-blood DNA from patients with FCDII and identified a brain somatic doublet mutation c.(A104T, C105A) in the Ras homolog, mTORC1 binding (RHEB) gene, which led to the RHEB p.Y35L mutation in one patient with FCDII. This RHEB mutation carrier had a dramatic increase of ribosomal protein S6 phosphorylation, indicating mTOR activation in the region of the brain lesion. The RHEB p.Y35L mutant protein had increased GTPλS-binding activity compared with wild-type RHEB. Overexpression of the RHEB p.Y35L variant in cultured cells also resulted in elevated S6 phosphorylation compared to wild-type RHEB. Importantly, in utero electroporation of the RHEB p.Y35L variant in mice induced S6 phosphorylation, cytomegalic neurons, dysregulated neuron migration, abnormal electroencephalogram, and seizures, all of which are found in patients with FCDII. Rapamycin treatment rescued abnormal electroencephalograms and alleviated seizures in these mice. These results demonstrate that brain somatic mutations in RHEB are also responsible for the pathogenesis of FCDII, indicating that aberrant activation of mTOR signaling is a primary driver and potential drug target for FCDII.