Stem cell quiescence acts as a tumor suppressor mechanism in hair follicle initiated squamous tumors
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ABSTRACT: 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 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:Mouse hair follicles undergo synchronized cycles. Cyclical regeneration and hair growth is fueled by hair follicle stem cells (HFSCs). We used ChIP-seq to unfold genome-wide chromatin landscapes of Nfatc1 and dissect the biological relevence of its upstream BMP signaling in HFSC aging. Telogen quiescent hair follicle stem cells (HFSCs) were FACS-purified for ChIP-sequcencing.
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:Piloerection (goosebump) requires concerted actions of the hair follicle, the arrector pili muscle (APM), and the sympathetic nerve, providing a model to study interactions across epithelium, mesenchyme, and nerves. Here, we show that APMs and sympathetic nerves form a dual component niche to modulate hair follicle stem cell (HFSC) activity. Sympathetic nerves form synapse-like structures with HFSCs and regulate HFSCs through norepinephrine, whereas APMs maintain sympathetic innervation to HFSCs. Without norepinephrine signaling, HFSCs enter a deep quiescence state by down-regulating cell cycle machinery and mitochondria metabolism, while up-regulating quiescence regulators Lhx2, Foxp1, and Fgf18. During development, HFSC progeny secrets Sonic Hedgehog (SHH) to direct the formation of this APM-sympathetic nerve niche, which in turn controls hair follicle regeneration in adults. Our results reveal a reciprocal interdependence between a regenerative tissue and its niche at different stages, and illustrate that nerves can modulate stem cell quiescence through synapses and neurotransmitters.
Project description:Tight immune defense against environment and a unique ability of self-repair are the hallmarks of epithelia. Here we show that innate immunity Toll like receptor 2 (TLR2) coordinates these key functions thereby promoting hair growth and tissue regeneration. TLR2 is enriched in hair follicle stem cells (HFSCs) and its levels change in hair cycle and skin disorders. The lack of TLR2 in HFSCs diminishes activation and proliferation of HFSCs markedly prolonging the resting phase of hair cycle. Transcriptome profiling of HFSCs revealed that TLR2 regulates main hair regeneration pathways. TLR2 deletion upregulates inhibitory BMP7 signaling, while the blockade by Noggin restores deficient HFSCs proliferation in the absence of TLR2. In injury model TLR2 is required for both, tissue and hair regeneration. While endothelial TLR2 drives wound revascularization and closure, HFSC TLR2 controls hair regrowth. Endogenous TLR2 ligand produced in hair follicles promotes hair regeneration and growth via HFSC TLR2. Together, HFSC TLR2 drives stem cell proliferation, hair cycle and regeneration.
Project description:Mouse hair follicles undergo synchronized cycles. Cyclical regeneration and hair growth is fueled by hair follicle stem cells (HFSCs). HFSCs regenerate hair in response to canonical Wnt signalling. We used RNA-seq to unfold genome-wide chromatin landscapes of β-catenin within the native HFSC-niche.
Project description:Hair loss is one of the typical aging phenotypes in mammals, yet the underlying mechanism(s) is unclear. Here we report that hair follicle stem cell (HFSC) aging causes the stepwise miniaturization of hair follicles and eventual hair loss both in wild-type mice and in humans. In vivo fate analysis of HFSCs revealed that the DNA damage response in HFSCs causes proteolysis of Type XVII Collagen (COL17A1/BP180) to trigger “HFSC aging”, characterized by their loss of stemness signature and epidermal commitment. Those aged HFSCs are cyclically eliminated from the skin through their terminal epidermal differentiation, thereby causing hair follicle miniaturization. That process can be recapitulated by Col17a1 deficiency and prevented by forced maintenance of COL17A1 in HFSCs, demonstrating that stem cell homeostasis is the keystone against ultimate execution of the tissue/organ aging program.
Project description:MiRNA-mediated regulation depends on the stoichiometry between miRNAs and their mRNA targets. To decipher dynamic function of this complex layer, it is critical to characterize individual miRNA species within a specific cellular context. Small RNA cloning followed by deep sequencing is uniquely positioned as a genome-wide profiling method to quantify miRNA expression with potentially unlimited dynamic range and provide single-nucleotide resolution for precise miRNA classification and de novo discovery. However, significant biases introduced by RNA ligation steps in the current RNA cloning protocol often lead to inaccurate miRNA quantification by >1000-fold deviation. As a result, it has greatly hindered the broad application of this method. Here we report a highly efficient RNA cloning method that achieves over 90% efficiency for both 5’ and 3’ ligations with diverse small RNA substrates. When applied to a pool of either equimolar or differentially mixed synthetic miRNAs, the deviation of the cloning frequency for each miRNA is minimized to less than 2-fold of the anticipated value. By using samples obtained from multiple tissues and cells, we further demonstrate the accurate quantification of miRNA expression over a dynamic range of four orders of magnitude. Our results also reveal that most cistronic miRNAs are expressed at similar levels and, in each cell population, miRNAs repress their cognate targets in a dosage dependent manner. Collectively, our high-efficiency RNA cloning method combining with deep sequencing establishes a cost-effective approach for accurate genome-wide miRNA profiling. We designed an artificial system composed of synthetic miRNAs for benchmarking biases in small RNA cDNA cloning for NGS.
Project description:Bioactive sphingolipids serve as an essential building block of membranes, forming a selective barrier ensuring subcellular compartmentalization and facilitating cell type-specific intercellular communication through regulation of the plasma membrane receptor repertoire. How the cell type-specific lipid compositions are achieved and what is their functional significance in tissue morphogenesis and maintenance has remained unclear. Here, we identify a stem-cell specific role for ceramide synthase 4 (CerS4) in orchestrating fate decisions in the skin epidermis. Deletion of CerS4 in the epidermis prevents the effective establishment of the adult hair follicle bulge stem cell (HFSCs) niche due to altered differentiation trajectories of HFSC precursors towards upper hair follicle and inner bulge fates. Mechanistically, the HFSC differentiation defects arise from a stem cell intrinsic imbalance of key ceramides and sphingolipids, and associated hyperactivity of canonical Wnt signaling. The lack of HFSCs leads to disruption of hair follicle architecture and hair follicle barrier function, ultimately triggering a Th2-dominated immune infiltration closely resembling human atopic dermatitis. This work uncovers a fundamental role for a cell state-specific sphingolipid profile in epidermal stem cell homeostasis and the role of an intact stem cell niche in maintaining an intact skin barrier.
Project description:Hair follicle (HF) regeneration begins when communication between quiescent epithelial stem cells (SCs) and underlying mesenchymal dermal papillae (DP) generates sufficient activating cues to overcome repressive BMP signals from surrounding niche cells. We uncovered a hitherto unrecognized DP transmitter, TGFβ2, which activates Smad2/3 transiently in HFSCs concomitant with entry into tissue regeneration. We used microarrays to detect the genes specifically affected by TGFß receptor II-deficient mice upon HFSC activation. Hair follicle stem cells (HFSCs) of hair gem (HG) and bulge, and total skin keratinocytes were FACS-purified from the mouse back skin at 2nd telogen-to-anagen transition stages.