Project description:Chronic, sustained exposure to stressors can profoundly impact tissue homeostasis, although the mechanisms by which these changes occur are largely unknown. Here, we report the adrenal gland-derived stress hormone corticosterone (the rodent equivalent of cortisol) regulates hair follicle stem cell (HFSC) quiescence and hair growth in mice. Without systemic corticosterone, HFSCs enter substantially more rounds of the regeneration cycle throughout life. Conversely, under chronic stress, elevated corticosterone levels prolong HFSC quiescence and keep hair follicles in an extended resting phase. Mechanistically, corticosterone acts on dermal papilla (DP) to suppress the expression of a secreted factor, Growth Arrest Specific 6 (Gas6). Restoring Gas6 expression overcomes stress-induced inhibition of HFSC activation and hair growth. Our work identifies corticosterone as a systemic inhibitor of HFSC activity via its impact on the niche, and demonstrates that removal of such inhibition drives HFSCs into frequent regeneration cycles with no observable defects long-term.
Project description:Quiescent stem cells are periodically activated to maintain tissue homeostasis or occasionally called into action upon injury. Molecular mechanisms that constitutively maintain stem cell identity or promote stem cell proliferation and differentiation upon activation have been extensively studied. However, it is unclear how quiescent stem cells maintain identity and reinforce quiescence when they transition from quiescence to activation. Here we show mouse hair follicle stem cell compartment induces a transcription factor, Foxc1, when activated. Importantly, deletion of Foxc1 in the activated but not quiescent stem cells compromises stem cell identity, fails to re-establish quiescence and subsequently drives premature stem cell activation.These findings uncover a dynamic, cell-intrinsic mechanism employed by hair follicle stem cells to reinforce stemness in response to activation. Poly(A)-enriched transcriptome RNA-seq on HFSCs isolated in WT and K14Cre cKO mice at anagen and early telogen stage of hair cycle.
Project description:Quiescent stem cells are periodically activated to maintain tissue homeostasis or occasionally called into action upon injury. Molecular mechanisms that constitutively maintain stem cell identity or promote stem cell proliferation and differentiation upon activation have been extensively studied. However, it is unclear how quiescent stem cells maintain identity and reinforce quiescence when they transition from quiescence to activation. Here we show mouse hair follicle stem cell compartment induces a transcription factor, Foxc1, when activated. Importantly, deletion of Foxc1 in the activated but not quiescent stem cells compromises stem cell identity, fails to re-establish quiescence and subsequently drives premature stem cell activation.These findings uncover a dynamic, cell-intrinsic mechanism employed by hair follicle stem cells to reinforce stemness in response to activation.
Project description:In many organs, adult stem cells are uniquely poised to serve as cancer cells of origin. In the epidermis, hair follicle stem cells (HFSCs) cycle through stages of quiescence (telogen) and proliferation (anagen) to drive hair growth. Within the hair follicle, HFSCs are capable of initiating squamous cell carcinoma, yet it is unclear how the hair cycle contributes to tumorigenesis. The data presented here show that HFSCs are unable to initiate tumors during the quiescent phase of the hair cycle, indicating that the mechanisms that keep HFSCs dormant are dominant to gain of oncogenes (Ras) or loss of tumor suppressors (p53). Instead, prolonged oncogenic stimuli only exert their effects when HFSC quiescence mechanisms are removed by normal HFSC activation. Furthermore, Pten activity is necessary for quiescence based tumor suppression, since Pten deletion alleviates this stem cell specific ability without affecting proliferation per se. Small RNAs were cloned from Trizol-lysed cells sorted from mouse skin and sequenced with the Illumina HiSeq2000.
Project description:In some organs, adult stem cells are uniquely poised to serve as cancer cells of origin1-4. It is unclear, however, whether tumorigenesis is influenced by the activation state of the adult stem cell. Hair follicle stem cells (HFSCs) act as cancer cells of origin for cutaneous squamous cell carcinoma (SCC) and undergo defined cycles of quiescence and activation. The data presented here show that HFSCs are unable to initiate tumors during the quiescent phase of the hair cycle, indicating that the mechanisms that keep HFSCs dormant are dominant to the gain of oncogenes (Ras) or the loss of tumor suppressors (p53). Furthermore, Pten activity is necessary for quiescence based tumor suppression, as its deletion alleviates tumor suppression without affecting proliferation. These data demonstrate that stem cell quiescence is a form of tumor suppression in HFSCs, and that Pten plays a role in maintaining quiescence in the presence of tumorigenic stimuli. This experiment includes RNA profiling of hair follicle stem cells at various stages of tumorigenesis Briefly: HFSCs were lineage traced with YFP allele, FACS isolated from various genotypes, and then profiled by Affymetrix microarray Cell Isolation and FACS: Whole dorsal and ventral mouse K15-CrePR; LSLYFP, K15-CrePR; KrasG12D; LSLYFP and K15-CrePR; KrasG12D; Ptenff; LSLYFP was extracted, diced and digested with collagenase (20mg/ml) for 2 hours at 37C, then an equal volume of .25% trypsin was added and digestion continued for an additional hour at 37C. Digested tissue was mechanically dispersed via pipette and filtered with a 100uM cell strainer, collected at 300g and washed twice with PBS. The cells were then filtered through a 40uM cell strainer and FACS processed. YFP+ and YFP- cell populations were collected in RNA lysis buffer (Stratagene) and stored at -80C. Gene expression profiling Microarray analyses by GeneSpring software were performed
Project description:DNA damage represents one of the cell intrinsic causes of stem cell aging, which leads to differentiation induced removal of damaged stem cells in skin and blood. Dietary restriction (DR) retards aging across various species including several strains of laboratory mice. Whether, DR has the potential to ameliorate DNA damage driven stem cell exhaustion remains incompletely understood. Here, we show that DR strongly extends the time to hair graying in response to γ–irradiation (IR) induced DNA damage of C57BL/6J mice. The study shows that DR prolongs quiescence of hair follicle stem cells (HFSCs) by silencing gene regulatory networks and metabolic switches that control proliferation and tissue regeneration. DR-mediated prolongation of HSFC quiescence blocks hair growth and prevents the depletion of HFSCs and ckit+ melanoblasts in response to IR. However, prolongation of HSFCs quiescence also leads to a suppression of DNA repair pathways and cannot prevent melanoblast loss and hair graying in the long run, when hair cycling is re- initiated even after extended periods of time. Together, these results support a model indicating that nutrient deprivation can delay but not heal DNA damage driven extinction of HFSCs and melanoblasts by stalling HSFCs in a prolonged state of quiescence coupled with inhibition of DNA repair. Disconnecting these two types of responses to DR could have the potential to delay stem cell aging.
Project description:In some organs, adult stem cells are uniquely poised to serve as cancer cells of origin1-4. It is unclear, however, whether tumorigenesis is influenced by the activation state of the adult stem cell. Hair follicle stem cells (HFSCs) act as cancer cells of origin for cutaneous squamous cell carcinoma (SCC) and undergo defined cycles of quiescence and activation. The data presented here show that HFSCs are unable to initiate tumors during the quiescent phase of the hair cycle, indicating that the mechanisms that keep HFSCs dormant are dominant to the gain of oncogenes (Ras) or the loss of tumor suppressors (p53). Furthermore, Pten activity is necessary for quiescence based tumor suppression, as its deletion alleviates tumor suppression without affecting proliferation. These data demonstrate that stem cell quiescence is a form of tumor suppression in HFSCs, and that Pten plays a role in maintaining quiescence in the presence of tumorigenic stimuli. This experiment includes RNA profiling of hair follicle stem cells at various stages of tumorigenesis
Project description:In many organs, adult stem cells are uniquely poised to serve as cancer cells of origin. In the epidermis, hair follicle stem cells (HFSCs) cycle through stages of quiescence (telogen) and proliferation (anagen) to drive hair growth. Within the hair follicle, HFSCs are capable of initiating squamous cell carcinoma, yet it is unclear how the hair cycle contributes to tumorigenesis. The data presented here show that HFSCs are unable to initiate tumors during the quiescent phase of the hair cycle, indicating that the mechanisms that keep HFSCs dormant are dominant to gain of oncogenes (Ras) or loss of tumor suppressors (p53). Instead, prolonged oncogenic stimuli only exert their effects when HFSC quiescence mechanisms are removed by normal HFSC activation. Furthermore, Pten activity is necessary for quiescence based tumor suppression, since Pten deletion alleviates this stem cell specific ability without affecting proliferation per se.
Project description:Stem cell quiescence preserves the cell reservoir by minimizing cell division over extended periods of time. Self-renewal of quiescent stem cells (SCs) requires the reentry into the cell cycle. In this study, we show that murine hair follicle SCs induce the Foxc1 transcription factor when activated. Deleting Foxc1 in activated, but not quiescent, SCs causes failure of the cells to reestablish quiescence and allows premature activation. Deleting Foxc1 in the SC niche of gene-targeted mice leads to loss of the old hair without impairing quiescence. In self-renewing SCs, Foxc1 activates Nfatc1 and bone morphogenetic protein (BMP) signaling, two key mechanisms that govern quiescence. These findings reveal a dynamic, cell-intrinsic mechanism used by hair follicle SCs to reinforce quiescence upon self-renewal and suggest a unique ability of SCs to maintain cell identity.
Project description:We investigated which signaling pathways downstream of Gas6/Axl promote the invasive phenotype of liver cancer cells. Thus, we performed phospho-proteomic analysis of MR hepatocytes and those expressing Axl (MR-Axl) in the presence and absence of Gas6. Protein-clustering based on the pattern of phosphorylation across the conditions and samples revealed four clusters: phospho-sites that are upregulated dependent on Axl expression (cluster 1) or Gas6 expression (cluster 2) and phospho-sites that are downregulated dependent on Axl expression (cluster 3) or Gas6 expression (cluster 4). Functional enrichment analysis showed enrichment of protein sets associated with cellular polarity and motility depending on changes in Axl expression and Gas6 activation. Furthermore, we analyzed phospho-proteomic data to estimate the activity of kinases based on kinase-substrate interactions using PhosR. Kinase perturbation analysis indicated mammalian target of rapamycin (mTOR) as the one with the highest upregulated activity in Gas6-stimulated MR-Axl cells compared to Gas6-stimulated MR cells. Accordingly, we analyzed substrates of mTOR and found that phosphorylation of Akt1 (Ser473) was upregulated in cluster 1 and highly increased in Gas6-stimulated MR-Axl, suggesting that Akt is regulated by Axl.