Specific knockout of Sox2 in astrocytes reduces reactive astrocyte formation and promotes recovery after early postnatal traumatic brain injury in mouse cortex.

In response to central nervous system (CNS) injury, astrocytes go through a series of alterations, referred to as reactive astrogliosis, ranging from changes in gene expression and cell hypertrophy to permanent astrocyte borders around stromal cell scars in CNS lesions. The mechanisms underlying injury-induced reactive astrocytes in the adult CNS have been extensively studied. However, little is known about injury-induced reactive astrocytes during early postnatal development. Astrocytes in the mouse cortex are mainly produced through local proliferation during the first 2 weeks after birth. Here we show that Sox2, a transcription factor critical for stem cells and brain development, is expressed in the early postnatal astrocytes and its expression level was increased in reactive astrocytes after traumatic brain injury (TBI) at postnatal day (P) 7 in the cortex. Using a tamoxifen-induced hGFAP-CreERT2; Sox2flox/flox ; Rosa-tdT mouse model, we found that specific knockout of Sox2 in astrocytes greatly inhibited the proliferation of reactive astrocytes, the formation of glia limitans borders and subsequently promoted the tissue recovery after postnatal TBI at P7 in the cortex. In addition, we found that injury-induced glia limitans borders were still formed at P2 in the wild-type mouse cortex, and knockout of Sox2 in astrocytes inhibited the reactivity of both astrocytes and microglia. Together, these findings provide evidence that Sox2 is essential for the reactivity of astrocytes in response to the cortical TBI during the early postnatal period and suggest that Sox2-dependent astrocyte reactivity is a potential target for therapeutic treatment after TBI.

Sex-specific hypothalamic neuropathology and glucose metabolism in an amyloidosis transgenic mouse model of Alzheimer's disease.

BACKGROUND: Amyloid toxicity and glucose metabolic disorders are key pathological features during the progression of Alzheimer's disease (AD). While the hypothalamus plays a crucial role in regulating systemic energy balance, the distribution of amyloid plaques in the preoptic, anterior, tuberal, and mammillary regions of the hypothalamus in AD mice, particularly across both sexes, remains largely unclear. Our ongoing research aims to explore hypothalamic neuropathology and glucose metabolic disturbances in a well-described APP/PS1 mouse model of AD. RESULTS: Immunocytochemical staining revealed that Old-AD-Female mice exhibited a greater hypothalamic Amyloid ß (Aß) burden than their Old-AD-Male counterparts, with the mammillary bodies showing the most severe accumulation. Analysis of ionized calcium binding adaptor molecule 1 (IBA1) immunoreactivity and Iba1 mRNA indicated differential microgliosis based on sex, while tanycytic territory and ZO-1 tight junction protein expression remained stable in AD mice. Moreover, sex-specific peripheral glucose metabolic parameters (random and fasting blood glucose) seemed to be exacerbated by age. Old AD mice of both sexes exhibited limited hypothalamic activation (c-Fos + cells) in response to blood glucose fluctuations. Hypothalamic Glut 1 expression decreased in young but increased in old female AD mice compared with age-matched male AD mice. Pearson correlation analysis further supported a negative correlation between hypothalamic Aß load and random blood glucose in old AD groups of both genders, shedding light on the mechanisms underlying this amyloidosis mouse model. CONCLUSION: Aged APP/PS1 mice exhibit sex-specific hypothalamic neuropathology and differential glucose metabolism, highlighting distinct pathological mechanisms within each gender.

Potential role of tanycyte-derived neurogenesis in Alzheimer's disease.

Tanycytes, specialized ependymal cells located in the hypothalamus, play a crucial role in the generation of new neurons that contribute to the neural circuits responsible for regulating the systemic energy balance. The precise coordination of the gene networks controlling neurogenesis in naive and mature tanycytes is essential for maintaining homeostasis in adulthood. However, our understanding of the molecular mechanisms and signaling pathways that govern the proliferation and differentiation of tanycytes into neurons remains limited. This article aims to review the recent advancements in research into the mechanisms and functions of tanycyte-derived neurogenesis. Studies employing lineage-tracing techniques have revealed that the neurogenesis specifically originating from tanycytes in the hypothalamus has a compensatory role in neuronal loss and helps maintain energy homeostasis during metabolic diseases. Intriguingly, metabolic disorders are considered early biomarkers of Alzheimer's disease. Furthermore, the neurogenic potential of tanycytes and the state of newborn neurons derived from tanycytes heavily depend on the maintenance of mild microenvironments, which may be disrupted in Alzheimer's disease due to the impaired blood-brain barrier function. However, the specific alterations and regulatory mechanisms governing tanycyte-derived neurogenesis in Alzheimer's disease remain unclear. Accumulating evidence suggests that tanycyte-derived neurogenesis might be impaired in Alzheimer's disease, exacerbating neurodegeneration. Confirming this hypothesis, however, poses a challenge because of the lack of long-term tracing and nucleus-specific analyses of newborn neurons in the hypothalamus of patients with Alzheimer's disease. Further research into the molecular mechanisms underlying tanycyte-derived neurogenesis holds promise for identifying small molecules capable of restoring tanycyte proliferation in neurodegenerative diseases. This line of investigation could provide valuable insights into potential therapeutic strategies for Alzheimer's disease and related conditions.