The role of nicotinamide phosphoribosyltransferase (Nampt) in hippocampal neural stem/progenitor cells
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ABSTRACT: Neural stem/progenitor cell (NSPC) proliferation and self-renewal, as well as insult-induced differentiation, decrease markedly with age, but the molecular mechanisms responsible for these declines remain unclear. Here we show that levels of NAD+ and nicotinamide phosphoribosyltransferase (Nampt), the rate-limiting enzyme in mammalian NAD+ biosynthesis, decrease with age in the hippocampus. Ablation of Nampt in adult NSPCs reduced their pool and proliferation in vivo. The decrease in the NSPC pool during aging can be rescued by enhancing hippocampal NAD+ levels. Nampt is the main source of NSPC NAD+ levels and required for G1/S progression of the NSPC cell cycle. Nampt is also critical for oligodendrocytic lineage fate decisions through a mechanism mediated redundantly by Sirt1 and Sirt2. Ablation of Nampt in the adult NSPCs in vivo reduced NSPC-mediated oligodendrogenesis upon injury. These phenotypes recapitulate defects in NSPCs during aging, implicating Nampt-mediated NAD+ biosynthesis as a mediator of these age-associated functional declines. Total RNA obtained from neurospheres derived from postnatal hippocampi subjected to 48 hours in vitro of incubation with Nampt-specific inhibitor FK866 (10 nM, 4 samples) or vehicle (DMSO, 1:1000, 4 samples).
Project description:Neural stem/progenitor cell (NSPC) proliferation and self-renewal, as well as insult-induced differentiation, decrease markedly with age, but the molecular mechanisms responsible for these declines remain unclear. Here we show that levels of NAD+ and nicotinamide phosphoribosyltransferase (Nampt), the rate-limiting enzyme in mammalian NAD+ biosynthesis, decrease with age in the hippocampus. Ablation of Nampt in adult NSPCs reduced their pool and proliferation in vivo. The decrease in the NSPC pool during aging can be rescued by enhancing hippocampal NAD+ levels. Nampt is the main source of NSPC NAD+ levels and required for G1/S progression of the NSPC cell cycle. Nampt is also critical for oligodendrocytic lineage fate decisions through a mechanism mediated redundantly by Sirt1 and Sirt2. Ablation of Nampt in the adult NSPCs in vivo reduced NSPC-mediated oligodendrogenesis upon injury. These phenotypes recapitulate defects in NSPCs during aging, implicating Nampt-mediated NAD+ biosynthesis as a mediator of these age-associated functional declines.
Project description:The transition between quiescence and activation in neural stem and progenitor cells (NSPCs) is coupled to reversible changes in energy metabolism with key implications for life-long NSPC self-renewal and neurogenesis. How this metabolic plasticity is ensured between NSPC activity states is unclear. We find that a state-specific rewiring of the mitochondrial proteome by the i-AAA peptidase YME1L is required to preserve NSPC self-renewal. YME1L controls the abundance of numerous mitochondrial substrates in quiescent NSPCs, and its deletion activates a differentiation program characterized by broad metabolic changes causing the irreversible shift away from a fatty acid oxidation-dependent state. Conditional Yme1l deletion in adult NSPCs in vivo results in defective self-renewal and premature differentiation, ultimately leading to NSPC pool depletion. Our results disclose an important role for YME1L in coordinating the switch between metabolic states of NSPCs and suggest that NSPC fate is regulated by compartmentalized changes in protein network dynamics.
Project description:Adult hippocampal neurogenesis is important for certain forms of cognition and failing neurogenesis has been implicated in neuropsychiatric diseases. The neurogenic capacity of hippocampal neural stem/progenitor cells (NSPCs) depends on a balance between quiescent and proliferative states. However, how this balance is regulated remains poorly understood. Here we show that the rate of fatty acid oxidation (FAO) defines quiescence vs. proliferation in NSPCs. Quiescent NSPCs show high levels of carnitine palmitoyltransferase 1a (Cpt1a)-dependent FAO, which is downregulated in proliferating NSPCs. Pharmacological inhibition and conditional deletion of Cpt1a in vitro and in vivo leads to altered NSPC behavior, showing that Cpt1a-dependent FAO is required for stem cell maintenance and proper neurogenesis. Strikingly, experimental manipulation of malonyl-CoA, the metabolite that regulates levels of FAO, is sufficient to induce exit from quiescence and to enhance NSPC proliferation. Thus, the data presented here identify a shift in FAO metabolism that governs NSPC behavior and suggest an instructive role for fatty acid metabolism in regulating NSPC activity.
Project description:NAD is a ubiquitous electron carrier essential for energy metabolism and the post translational modification of numerous regulatory proteins. Perturbation of NAD metabolism is considered detrimental to health, with NAD depletion commonly thought to promote aging. However, the extent to which cellular NAD concentration can be decreased without deleterious repercussions is unclear. We generated a mouse model where nicotinamide phosphoribosyltransferase (NAMPT)-mediated NAD+ biosynthesis is disrupted in adult skeletal muscle. The resulting 85% decrease in muscle NAD+ abundance was associated with preserved tissue integrity and functionality, as demonstrated by its unchanged morphology, contractility, and exercise tolerance. This lack of defects was corroborated by intact mitochondrial respiratory capacity and unaffected muscle transcriptomic and proteomic profiles. Furthermore, lifelong NAD depletion did not accelerate muscle aging or impair whole-body metabolism. Collectively, these findings indicate that NAD depletion does not contribute to age related declines in skeletal muscle function.
Project description:Mammalian neural stem/progenitor cells (NSPCs) sequentially generate neurons and glia during central nervous system (CNS) development. Several transcription factors and microRNAs (miRNAs) are involved in the temporal regulation of NSPC differentiation. miRNA-153 (miR-153) as a modulator of NSPC specification. Overexpression (OE) of miR-153 delayed the onset of astrogliogenesis and maintained NSPCs in an undifferentiated state in vitro. miR-153-OE and control NSPCs (tertiary neurospheres (TNs) derived from mouse ES Cells via embryoid body formation) subjected to the gene expression microarray analysis.
Project description:The transition between quiescence and activation in neural stem and progenitor cells (NSPCs) is coupled to reversible changes in energy metabolism with key implications for life-long NSPC self-renewal and neurogenesis. How this metabolic plasticity is ensured between NSPC activity states is unclear. We find that a state-specific rewiring of the mitochondrial proteome by the i-AAA peptidase YME1L is required to preserve NSPC self-renewal. YME1L controls the abundance of numerous mitochondrial substrates in quiescent NSPCs, and its deletion activates a differentiation program characterized by broad metabolic changes causing the irreversible shift away from a fatty acid oxidation-dependent state. Conditional Yme1l deletion in adult NSPCs in vivo results in defective self-renewal and premature differentiation, ultimately leading to NSPC pool depletion. Our results disclose an important role for YME1L in coordinating the switch between metabolic states of NSPCs and suggest that NSPC fate is regulated by compartmentalized changes in protein network dynamics.
Project description:Neural stem/progenitor cells (NSPCs) generate new neurons throughout adulthood. However, the underlying regulatory processes are still not fully understood. Lipid metabolism plays an important role in regulating NSPC activity: build-up of lipids is crucial for NSPC proliferation, whereas break-down of lipids has been shown to regulate NSPC quiescence. Despite their central role for cellular lipid metabolism, the role of lipid droplets (LDs), the lipid storing organelles, in NSPCs remains underexplored. Here we show that LDs are highly abundant in adult mouse NSPCs, and that LD accumulation is significantly altered upon fate changes such as quiescence and differentiation. NSPC proliferation is influenced by the number of LDs, inhibition of LD build-up, breakdown or usage, and the asymmetric inheritance of LDs during mitosis. Furthermore, high LD-containing NSPCs have increased metabolic activity and capacity, but do not suffer from increased oxidative damage. Together, these data indicate an instructive role for LDs in driving NSPC behaviour.
Project description:In order to investigate the role of Mina53 in the NSPC proliferation and differentiation, we performed RNA-seq using Mina53-KO NSPCs and wild-type NSPCs; we performed CUT-TAG using anti-H4R3me2a antibody in Mina53-KO NSPCs and wild-type NSPCs.
Project description:Mechanisms controlling the proliferative activity of neural stem/progenitor cells (NSPCs) play a pivotal role to ensure life-long neurogenesis in the mammalian brain. How metabolic programs are coupled with NSPC activity remains unknown. Here we show that fatty acid synthase (FASN), the key enzyme of de novo lipogenesis, is highly active in adult NSPCs and that conditional deletion of FASN in NSPCs impairs adult neurogenesis. The rate of de novo lipid synthesis and subsequent proliferation of NSPCs is regulated by Spot14, a gene we found to be selectively expressed in low proliferating adult NSPCs. Spot14 reduces the availability of malonyl-CoA, which is an essential substrate for FASN to fuel lipogenesis. Thus, we here identified a functional coupling between the regulation of lipid metabolism and adult NSPC proliferation. 6 samples were analyzed. Spot14+: Spot14 GFP positive mouse neural stem cell, 3 biological rep Spot14-: Spot14 GFP negative mouse neural stem cell, 3 biological rep
Project description:In selected tissutal niches of the adult mouse brain, such as the subventricular zone (SVZ) underlying the lateral ventricles, neurogenesis persists thanks to a population of quiescent neural stem cells, which can be activated (aNSCs) by extrinsic stimuli to initiate proliferation and generate a neurogenic lineage consisting of transit amplifying progenitors (TAPs), neuroblasts (NBs) and newborn neurons. This process is markedly reduced during aging, which might contribute to the cognitive decline of elderly subjects. Recent studies suggest that the aged niche environment may decrease the pool of proliferating neural/stem progenitor cells (NSPCs), and hence adult neurogenesis, by causing transcriptomic changes that favour NSC quiescence over activation. The transcription factors that mediate these changes, however, remain largely unclear. We previously found that the homeobox gene Dbx2 is upregulated in NSPCs of the aged mouse SVZ and can inhibit the growth of young adult NSPC cultures. Here, we show that Dbx2 expression is downregulated by Epidermal Growth Factor Receptor signalling, which promotes NSPC proliferation and decreases in the aged SVZ. By means of transgenic NSPC lines, we also show that Dbx2 inhibits NSPC proliferation by hindering the G1/S and the G2/M transition. Furthermore, we exploit RNA sequencing of transgenic NSPCs to elucidate the transcriptional networks modulated by Dbx2. Among the top hits, we report the downregulation of several gene categories implicated in cell cycle progression. Accordingly, we find that Dbx2 function is negatively correlated with the transcriptional signatures of proliferative NSPCs (aNSCs, TAPs and early NBs). Altogether, these results point to Dbx2 as a potential molecular node relaying the extracellular anti-neurogenic input of the aged niche to the NSPC transcriptome.