Project description:Skeletal muscle aging results in a gradual loss of skeletal muscle mass, skeletal muscle function and decreased regenerative capacity, which can lead to sarcopenia and increased mortality. While the mechanisms underlying sarcopenia remain unclear, the skeletal muscle stem cell, or satellite cell, is required for muscle regeneration. Therefore, identification of signaling pathways affecting satellite cell function during aging may provide insights into therapeutic targets for combating sarcopenia. Here, we show that a cell-autonomous loss in self-renewal occurs via novel alterations in FGF and p38αβ MAPK signaling in old satellite cells. We further demonstrate that pharmacological manipulation of these pathways can ameliorate age-associated self-renewal defects. Thus, our data highlight an age-associated deregulation of a satellite cell homeostatic network and reveals potential therapeutic opportunities for the treatment of progressive muscle wasting. Satellite cells were isolated from young (3-6mo) and aged (20-25mo) adult mice; individual date files represent 2 independent pools of RNA from 4-8 mice at each timepoint.
Project description:Skeletal muscle aging results in a gradual loss of skeletal muscle mass, skeletal muscle function and decreased regenerative capacity, which can lead to sarcopenia and increased mortality. While the mechanisms underlying sarcopenia remain unclear, the skeletal muscle stem cell, or satellite cell, is required for muscle regeneration. Therefore, identification of signaling pathways affecting satellite cell function during aging may provide insights into therapeutic targets for combating sarcopenia. Here, we show that a cell-autonomous loss in self-renewal occurs via novel alterations in FGF and p38αβ MAPK signaling in old satellite cells. We further demonstrate that pharmacological manipulation of these pathways can ameliorate age-associated self-renewal defects. Thus, our data highlight an age-associated deregulation of a satellite cell homeostatic network and reveals potential therapeutic opportunities for the treatment of progressive muscle wasting.
Project description:MTD project_description Inflammation and decreased stem cell function characterize organism aging, yet the relationship between these factors remains incompletely understood. This study shows that aged hematopoietic stem and progenitor cells exhibit increased ground-stage NF-κB activity, which enhances their responsiveness to undergo differentiation and loss of self-renewal in response to inflammation. The study identifies Rad21/cohesin as a critical mediator of NF-κB signals, by increasing chromatin accessibility of inter-/intra-genic and enhancer regions. Rad21/NF-κB are required for normal differentiation, but limit self-renewal of hematopoietic stem cells (HSCs) during aging and inflammation in an NF-κB dependent manner. HSCs from aged mice fail to downregulate Rad21/cohesin and inflammation/differentiation inducing signals in the resolution phase after acute inflammation. and The inhibition of cohesin/NF-κB is sufficient to revert the hypersensitivity of aged HSPCs to inflammation-induced differentiation. During aging, myeloid-biased HSCs with disrupted and naturally occurring reduced expression of Rad21/cohesin are increasingly selected over lymphoid-biased HSCs. Together, Rad21/cohesin mediated NF-κB signaling limits HSPC function during aging and selects for cohesin deficient HSCs with myeloid skewed differentiation.
Project description:Hematopoietic cell fate decisions such as self-renewal and differentiation are highly regulated through multiple molecular pathways. One pathway, the ubiquitin proteasome system (UPS), controls protein levels by tagging them with polyubiquitin chains and promoting their degradation through the proteasome. Ubiquitin E3 ligases serve as the substrate-recognition component of the UPS. Through investigating the FBOX family of E3 ligases, we discovered that Fbxo21 was highly expressed in the hematopoietic stem and progenitor cell (HSPC) population, and showed low to no expression in mature myeloid populations. To determine the role of FBXO21 on HSPC maintenance, self-renewal, and differentiation, we generated shRNAs against FBXO21 and a hematopoietic specific Fbxo21 conditional knockout (cKO) mouse model. We found that silencing FBXO21 in HSPCs led to a loss in colony formation and an increase in cell differentiation in vitro. Additionally, stressing the HSPC populations in our Fbxo21 cKO mouse with 5-FU injections resulted in a decrease in survival, despite these populations showing minimal alterations during steady-state hematopoiesis. Although FBXO21 has previously been proposed to regulate cytokine signaling via ASK and p38, our results show that depletion of FBXO21 led to altered ERK signaling in vitro. Together, these findings suggest ubiquitin E3 ligase FBXO21 regulates HSPCs through cytokine mediated pathways.
Project description:Satellite cells are responsible for the long-term regenerative capacity of adult skeletal muscle. The diminished muscle performance and regenerative capacity of aged muscle is thought to reflect progressive fibrosis and atrophy. Whether this reduction in muscle competency also involves a diminishment in the intrinsic regulation of satellite cell self-renewal remains unknown. We used microarray to identify gene expression changes underlying the marked reduction in the capacity of satellite cells to self-renew, contribute to regeneration and repopulate the niche as they age.
Project description:Self-renewal programs in leukemia stem cells (LSCs) predict poor prognosis in acute myeloid leukemia (AML) patients. We identified CD4+ T cell-derived interleukin (IL) 21 as an important negative regulator of self-renewal of murine and human LSCs, but not hematopoietic stem cells. IL21/IL21R signaling favored asymmetric cell division and differentiation in LSCs through accumulation of reactive oxygen species (ROS) and activation of p38-MAPK signaling, resulting in reduced LSCs number and significantly prolonged survival in murine AML models. In human AML, serum IL21 at diagnosis was identified as an independent positive prognostic biomarker for outcome and correlated with better survival and higher complete remission rate in patients that underwent high-dose chemotherapy. IL21 inhibited primary AML LSCs function in vitro by activating ROS and p38-MAPK signaling and this effect was enhanced by cytarabine treatment. Consequently, promoting IL21/IL21R signaling on LSCs may be a novel approach to decrease stemness and increase differentiation in AML.
Project description:Self-renewal programs in leukemia stem cells (LSCs) predict poor prognosis in acute myeloid leukemia (AML) patients. We identified CD4+ T cell-derived interleukin (IL) 21 as an important negative regulator of self-renewal of murine and human LSCs, but not hematopoietic stem cells. IL21/IL21R signaling favored asymmetric cell division and differentiation in LSCs through accumulation of reactive oxygen species (ROS) and activation of p38-MAPK signaling, resulting in reduced LSCs number and significantly prolonged survival in murine AML models. In human AML, serum IL21 at diagnosis was identified as an independent positive prognostic biomarker for outcome and correlated with better survival and higher complete remission rate in patients that underwent high-dose chemotherapy. IL21 inhibited primary AML LSCs function in vitro by activating ROS and p38-MAPK signaling and this effect was enhanced by cytarabine treatment. Consequently, promoting IL21/IL21R signaling on LSCs may be a novel approach to decrease stemness and increase differentiation in AML.
Project description:Self-renewal programs in leukemia stem cells (LSCs) predict poor prognosis in acute myeloid leukemia (AML) patients. We identified CD4+ T cell-derived interleukin (IL) 21 as an important negative regulator of self-renewal of murine and human LSCs, but not hematopoietic stem cells. IL21/IL21R signaling favored asymmetric cell division and differentiation in LSCs through accumulation of reactive oxygen species (ROS) and activation of p38-MAPK signaling, resulting in reduced LSCs number and significantly prolonged survival in murine AML models. In human AML, serum IL21 at diagnosis was identified as an independent positive prognostic biomarker for outcome and correlated with better survival and higher complete remission rate in patients that underwent high-dose chemotherapy. IL21 inhibited primary AML LSCs function in vitro by activating ROS and p38-MAPK signaling and this effect was enhanced by cytarabine treatment. Consequently, promoting IL21/IL21R signaling on LSCs may be a novel approach to decrease stemness and increase differentiation in AML.
Project description:NAD is an obligate co-factor for the catabolism of metabolic fuels in all cell types. However, the availability of NAD in several tissues can become limited during genotoxic stress and the course of natural aging. The point at which NAD restriction imposes functional limitations on tissue physiology remains unknown. We examined this question in murine skeletal muscle by specifically depleting Nampt, an essential enzyme in the NAD salvage pathway. Knockout mice exhibited a dramatic 85% decline in intramuscular NAD content, accompanied by fiber degeneration and progressive loss of both muscle strength and treadmill endurance. Administration of the NAD precursor nicotinamide riboside rapidly ameliorated functional deficits and restored muscle mass, despite having only a modest effect on the intramuscular NAD pool. Additionally, lifelong overexpression of Nampt preserved muscle NAD levels and exercise capacity in aged mice, supporting a critical role for tissue-autonomous NAD homeostasis in maintaining muscle mass and function. Messenger RNA was isolated from quadriceps muscle of mice from three different age groups and three different genotypes. Wildtype mice were aged 4, 7, and 24 months. Mice deficient for Nampt in skeletal muscle (mNKO) were aged 7 months. Mice overexpressing Nampt in skeletal muscle were aged 4 and 24 months.