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Sox10 is a well-known factor to control oligodendrocyte (OL) differentiation and its expression is regulated by Olig2. As an important protein kinase, Akt has been implicated in diseases with white matter (WM) abnormalities. To study whether and how Akt may regulate OL development, we generated OL lineage cells-specific Akt1/Akt2/Akt3 triple conditional knockout (Akt cTKO) mice. Both male and female mice were used. These mutants exhibit complete loss of mature OLs and unchanged apoptotic cell death in the central nervous system. We show that deletion of Akt three isoforms causes down-regulation of Sox10 and decreased levels of phosphorylated FoxO1 (pFoxO1) in the brain. In vitro analysis reveals that expression of FoxO1 with mutations on phosphorylation sites for Akt significantly represses the Sox10 promoter activity, suggesting that phosphorylation of FoxO1 by Akt is important for Sox10 expression. We further demonstrate that mutant FoxO1 without Akt phosphorylation epitopes is enriched in the Sox10 promoter. Together, this study identifies a novel FoxO1 phosphorylation-dependent mechanism for Sox10 expression and OL differentiation. SIGNIFICANCE STATEMENT Dysfunction of Akt is associated with white matter diseases including the agenesis of the corpus callosum. However, it remains unknown whether Akt plays an important role in oligodendrocyte differentiation. To address this question, we generated oligodendrocyte lineage cells-specific Akt1/Akt2/Akt3 triple conditional knockout mice. Akt mutants exhibit deficient white matter development, loss of mature oligodendrocytes, absence of myelination and unchanged apoptotic cell death in the central nervous system. We demonstrate that deletion of Akt three isoforms leads to down-regulation of Sox10, and that phosphorylation of FoxO1 by Akt is critical for Sox10 expression. Together, these findings reveal a novel mechanism to regulate Sox10 expression. This study may provide insights on molecular mechanisms for neurodevelopmental diseases caused by dysfunctions of protein kinases.

Mutations on γ-secretase subunits are associated with neurologic diseases. Whereas the role of γ-secretase in neurogenesis has been intensively studied, little is known about its role in astrogliogenesis. Recent evidence has demonstrated that astrocytes can be generated from oligodendrocyte precursor cells (OPCs). However, it is not well understood what mechanism may control OPCs to differentiate into astrocytes. To address the above questions, we generated two independent lines of oligodendrocyte lineage-specific presenilin enhancer 2 (Pen-2) conditional KO mice. Both male and female mice were used. Here we demonstrate that conditional inactivation of Pen-2 mediated by Olig1-Cre or NG2-CreERT2 causes enhanced generation of astrocytes. Lineage-tracing experiments indicate that abnormally generated astrocytes are derived from Cre-expressing OPCs in the CNS in Pen-2 conditional KO mice. Mechanistic analysis reveals that deletion of Pen-2 inhibits the Notch signaling to upregulate signal transducer and activator of transcription 3, which triggers activation of GFAP to promote astrocyte differentiation. Together, these novel findings indicate that Pen-2 regulates the specification of astrocytes from OPCs through the signal transducer and activator of transcription 3 signaling. SIGNIFICANCE STATEMENT Astrocytes and oligodendrocyte (OLs) play critical roles in the brain. Recent evidence has demonstrated that astrocytes can be generated from OL precursor cells (OPCs). However, it remains poorly understood what mechanism governs the differentiation of OPCs into astrocytes. In this study, we took advantage of OL lineage cells specific presenilin enhancer 2 (Pen-2) conditional KO mice. We show that deletion of Pen-2 leads to dramatically enhanced astrocyte differentiation from OPCs in the CNS. Mechanistic analysis reveals that deletion of Pen-2 inhibits Hes1 and activates signal transducer and activator of transcription 3 to trigger GFAP activation which promotes astrocyte differentiation. Overall, this study identifies a novel function of Pen-2 in astrogliogenesis from OPCs.

Astrocytes play many important functions in response to spinal cord injury (SCI) in an activated manner, including clearance of necrotic tissue, formation of protective barrier, maintenance of microenvironment balance, interaction with immune cells, and formation of the glial scar. More and more studies have shown that the astrocytes are heterogeneous, such as inflammatory astrocyte 1 (A1) and neuroprotective astrocyte 2 (A2) types. However, the subtypes of astrocyte resulting from SCI have not been clearly defined. In this study, using single-cell RNA sequencing, we constructed the transcriptomic profile of astrocytes from uninjured spinal cord tissue and injured tissue nearby the lesion epicenter at 0.5, 1, 3, 7, 14, 60, and 90 days after mouse hemisection spinal cord surgery. Our analysis uncovered six transcriptionally distinct astrocyte states, including Atp1b2

Introduction Presenilin enhancer2 (Pen‐2) is an essential subunit of γ‐secretase, which is a key protease responsible for the cleavage of amyloid precursor protein (APP) and Notch. Mutations on Pen‐2 cause familial Alzheimer disease (AD). However, it remains unknown whether Pen‐2 regulates neuronal survival and neuroinflammation in the adult brain. Methods Forebrain neuron‐specific Pen‐2 conditional knockout (Pen‐2 cKO) mice were generated for this study. Pen‐2 cKO mice expressing Notch1 intracellular domain (NICD) conditionally in cortical neurons were also generated. Results Loss of Pen‐2 causes astrogliosis followed by age‐dependent cortical atrophy and neuronal loss. Loss of Pen‐2 results in microgliosis and enhanced inflammatory responses in the cortex. Expression of NICD in Pen‐2 cKO cortices ameliorates neither neurodegeneration nor neuroinflammation. Conclusions Pen‐2 is required for neuronal survival in the adult cerebral cortex. The Notch signaling may not be involved in neurodegeneration caused by loss of Pen‐2., This study reports a novel mouse model, which exhibits age‐related neurodegeneration. Forebrain neuron‐specific deletion of Pen‐2 leads to early astrogliosis followed by age‐dependent neuronal loss and severe inflammatory responses in the adult cerebral cortex. The Notch signaling does not play a critical role in Pen‐2‐dependent neuronal survival.

Prolonged neuroinflammation is a driving force for neurodegenerative disease, and agents against inflammatory responses are regarded as potential treatment strategies. Here we aimed to evaluate the prevention effects on gliosis by dexamethasone (DEX), an anti-inflammation drug. We used DEX to treat the nicastrin conditional knockout (cKO) mouse, a neurodegenerative mouse model. DEX (10 mg/kg) was given to 2.5-month-old nicastrin cKO mice, which have not started to display neurodegeneration and gliosis, for 2 months. Immunohistochemistry (IHC) and Western blotting techniques were used to detect changes in neuroinflammatory responses. We found that activation of glial fibrillary acidic protein (GFAP) positive or ionized calcium binding adapter molecule1 (Iba1) positive cells was not inhibited in nicastrin cKO mice treated with DEX as compared to those treated with saline. These data suggest that DEX does not prevent or ameliorate gliosis in a neurodegenerative mouse model when given prior to neuronal or synaptic loss.

Oligodendrocytes (OLs) and astrocytes play critical roles in a variety of brain functions. OL precursor cells (OPCs) are known to give rise to OLs as well as astrocytes. However, little is known about the mechanism by which OPCs determine their specification choice for OLs versus astrocytes in the central nervous system (CNS). Here we show that genetic inhibition of γ-secretase in OPCs reduces OL differentiation but enhances astrocyte specification. Mechanistic analysis reveals that inhibition of γ-secretase results in decreased levels of Hes1, and that Hes1 down-regulates the expression of signal transducer and activator of transcription3 (Stat3) via binding to specific regions of its promoter. We demonstrate that conditional inactivation of Stat3 in OL lineages restores the number of astrocytes in γ-secretase mutant mice. In summary, this study identifies a key mechanism which controls OPC’s specification choice for OL versus astrocyte during postnatal development. This γ-secretase-dependent machinery may be essential for the CNS to maintain the population balance between OLs and astrocytes.