Distribution of Aldh1L1-CreERT2 Recombination in Astrocytes Versus Neural Stem Cells in the Neurogenic Niches of the Adult Mouse Brain

In the adult central nervous system, neural stem cells (NSCs) reside in two discrete niches: the subependymal zone (SEZ) of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus (DG). Here, NSCs represent a population of highly specialized astrocytes that are able to proliferate and give rise to neuronal and glial progeny. This process, termed adult neurogenesis, is extrinsically regulated by other niche cells such as non-stem cell astrocytes. Studying these non-stem cell niche astrocytes and their role during adult neuro- and gliogenesis has been hampered by the lack of genetic tools to discriminate between transcriptionally similar NSCs and niche astrocytes. Recently, Aldh1L1 has been shown to be a pan-astrocyte marker and that its promoter can be used to specifically target astrocytes using the Cre-loxP system. In this study we explored whether the recently described Aldh1L1-CreERT2 mouse line (Winchenbach et al., 2016) can serve to specifically target niche astrocytes without inducing recombination in NSCs in adult neurogenic niches. Using short- and long-term tamoxifen protocols we revealed high recombination efficiency and specificity in non-stem cell astrocytes and little to no recombination in NSCs of the adult DG. However, in the SEZ we observed recombination in ependymal cells, astrocytes, and NSCs, the latter giving rise to neuronal progeny of the rostral migratory stream and olfactory bulb. Thus, we recommend the here described Aldh1L1-CreERT2 mouse line for predominantly studying the functions of non-stem cell astrocytes in the DG under physiological and pathological conditions

Two novel CreERT2 transgenic mouse lines to study melanocytic cells in vivo

Abstract The skin of adult mammals protects from radiation, physical and chemical insults. While melanocytes and melanocyte‐producing stem cells contribute to proper skin function in healthy organisms, dysfunction of these cells can lead to the generation of malignant melanoma—the deadliest type of skin cancer. Addressing cells of the melanocyte lineage in vivo represents a prerequisite for the understanding of melanoma on cellular level and the development of preventive and treatment strategies. Here, the inducible Cre‐loxP‐system has emerged as a promising tool to specifically target, monitor, and modulate cells in adult mice. Re‐analysis of existing sequencing data sets of melanocytic cells revealed that genes with a known function in neural cells, including neural stem cells (Aldh1L1 and Nestin), are also expressed in melanocytic cells. Therefore, in this study, we explored whether the promoter activity of Nestin and Aldh1L1 can serve to target cells of the melanocyte lineage using the inducible CreERT2‐loxP‐system. Using an immunohistochemical approach and different time points of analysis, we were able to map the melanocytic fate of recombined stem cells in the adult hair follicle of Nestin‐CreERT2 and Aldh1L1‐CreERT2 transgenic mice. Thus, we here present two new mouse models and propose their use to study and putatively modulate adult melanocytic cells in vivo

Sox9 regulates melanocytic fate decision of adult hair follicle stem cells

The bulge of hair follicles harbors Nestin+ (neural crest like) stem cells, which exhibit the potential to generate various cell types including melanocytes. In this study, we aimed to determine the role of Sox9, an important regulator during neural crest development, in melanocytic differentiation of those adult Nestin+ cells. Immunohistochemical analysis after conditional Sox9 deletion in Nestin+ cells of adult mice revealed that Sox9 is crucial for melanocytic differentiation of these cells and that Sox9 acts as a fate determinant between melanocytic and glial fate. A deeper understanding of factors that regulate fate decision, proliferation and differentiation of these stem cells provides new aspects to melanoma research as melanoma cells share many similarities with neural crest cells. In summary, we here show the important role of Sox9 in melanocytic versus glial fate decision of Nestin+ stem cells in the skin of adult mice

Mitochondrial Dysfunction in Astrocytes Impairs the Generation of Reactive Astrocytes and Enhances Neuronal Cell Death in the Cortex Upon Photothrombotic Lesion

Mitochondria are key organelles in regulating the metabolic state of a cell. In the brain, mitochondrial oxidative metabolism is the prevailing mechanism for neurons to generate ATP. While it is firmly established that neuronal function is highly dependent on mitochondrial metabolism, it is less well-understood how astrocytes function rely on mitochondria. In this study, we investigate if astrocytes require a functional mitochondrial electron transport chain (ETC) and oxidative phosphorylation (oxPhos) under physiological and injury conditions. By immunohistochemistry we show that astrocytes expressed components of the ETC and oxPhos complexes in vivo. Genetic inhibition of mitochondrial transcription by conditional deletion of mitochondrial transcription factor A (Tfam) led to dysfunctional ETC and oxPhos activity, as indicated by aberrant mitochondrial swelling in astrocytes. Mitochondrial dysfunction did not impair survival of astrocytes, but caused a reactive gliosis in the cortex under physiological conditions. Photochemically initiated thrombosis induced ischemic stroke led to formation of hyperfused mitochondrial networks in reactive astrocytes of the perilesional area. Importantly, mitochondrial dysfunction significantly reduced the generation of new astrocytes and increased neuronal cell death in the perilesional area. These results indicate that astrocytes require a functional ETC and oxPhos machinery for proliferation and neuroprotection under injury conditions

Four-and-a-Half LIM-Domain Protein 2 (FHL2) Induces Neuropeptide Y (NPY) in Macrophages in Visceral Adipose Tissue and Promotes Diet-Induced Obesity

Obesity is characterized by the expansion of the adipose tissue, usually accompanied by inflammation, with a prominent role of macrophages infiltrating the visceral adipose tissue (VAT). This chronic inflammation is a major driver of obesity-associated comorbidities. Four-and-a-half LIM-domain protein 2 (FHL2) is a multifunctional adaptor protein that is involved in the regulation of various biological functions and the maintenance of the homeostasis of different tissues. In this study, we aimed to gain new insights into the expression and functional role of FHL2 in VAT in diet-induced obesity. We found enhanced FHL2 expression in the VAT of mice with Western-type diet (WTD)-induced obesity and obese humans and identified macrophages as the cellular source of enhanced FHL2 expression in VAT. In mice with FHL2 deficiency (FHL2KO), WTD feeding resulted in reduced body weight gain paralleled by enhanced energy expenditure and uncoupling protein 1 (UCP1) expression, indicative of activated thermogenesis. In human VAT, FHL2 was inversely correlated with UCP1 expression. Furthermore, macrophage infiltration and the expression of the chemokine MCP-1, a known promotor of macrophage accumulation, was significantly reduced in WTD-fed FHL2KO mice compared with wild-type (wt) littermates. While FHL2 depletion did not affect the differentiation or lipid metabolism of adipocytes in vitro, FHL2 depletion in macrophages resulted in reduced expressions of MCP-1 and the neuropeptide Y (NPY). Furthermore, WTD-fed FHL2KO mice showed reduced NPY expression in VAT compared with wt littermates, and NPY expression was enhanced in VAT resident macrophages of obese individuals. Stimulation with recombinant NPY induced not only UCP1 expression and lipid accumulation but also MCP-1 expression in adipocytes. Collectively, these findings indicate that FHL2 is a positive regulator of NPY and MCP-1 expression in macrophages and herewith closely linked to the mechanism of obesity-associated lipid accumulation and inflammation in VAT. Thus, FHL2 appears as a potential novel target to interfere with the macrophage–adipocyte crosstalk in VAT for treating obesity and related metabolic disorders.</jats:p

Newborn Neurons in the Aged Hippocampus—Scarce and Slow but Highly Plastic

In this issue of Cell Reports, Trinchero et al. (2017) demonstrate that newborn neurons in the aged hippocampus are delayed in development but are highly susceptible to stimuli improving neuronal activity. This plasticity is mediated cell-intrinsically by neurotrophin signaling. : In this issue of Cell Reports, Trinchero et al. (2017) demonstrate that newborn neurons in the aged hippocampus are delayed in development but are highly susceptible to stimuli improving neuronal activity. This plasticity is mediated cell-intrinsically by neurotrophin signaling

In Vivo Targeting of Adult Neural Stem Cells in the Dentate Gyrus by a Split-Cre Approach

We describe the labeling of adult neural stem cells (aNSCs) in the mouse and human dentate gyrus (DG) by the combinatorial expression of glial fibrillary acidic protein (GFAP) and Prominin1, as revealed by immunohistochemistry. Split-Cre-based genetic fate mapping of these double-positive cells in the adult murine DG reveals their NSC identity, as they are self-renewing and contribute to neurogenesis over several months. Their progeny reacts to stimuli such as voluntary exercise with increased neurogenesis. Prominin1+/GFAP+ cells also exist in the adult human DG, the only region in the human brain for which adult neurogenesis has been consistently reported. Our data, together with previous evidence of such double-positive NSCs in the developing murine brain and in neurogenic regions of vertebrates with widespread neurogenesis, suggest that Prominin1- and GFAP-expressing cells are NSCs in a wide range of species in development and adulthood