A low quadriceps slow-twitch (ST), oxidative (relative to fast-twitch) fiber proportion is prevalent in chronic diseases such Chronic Obstructive Pulmonary Disease (COPD) and is associated with exercise limitation and poor outcomes. Benefits of an increased ST fiber proportion are demonstrated in genetically modified animals. Pathway analysis of published data of differentially expressed genes in mouse ST and FT fibers, mining of our microarray data and a qPCR analysis of quadriceps specimens from COPD patients and controls were performed. ST markers were quantified in C2C12 myotubes with EGF-neutralizing antibody, EGFR inhibitor or an EGFR-silencing RNA added. A zebrafish egfra mutant was generated by genome editing and ST fibers counted. EGF signaling was (negatively) associated with the ST muscle phenotype in mice and humans, and muscle EGF transcript levels were raised in COPD. In C2C12 myotubes, EGFR inhibition/silencing increased ST, including mitochondrial, markers. In zebrafish, egfra depletion increased ST fibers and mitochondrial content. EGF is negatively associated with ST muscle phenotype in mice, healthy humans and COPD patients. EGFR blockade promotes the ST phenotype in myotubes and zebrafish embryos. EGF signaling suppresses the ST phenotype, therefore EGFR inhibitors may be potential treatments for COPD-related muscle ST fiber loss.

Maintaining the architecture, size and composition of an intact stem cell (SC) compartment is crucial for tissue homeostasis and regeneration throughout life. In mammalian skin, elevated expression of the anti-apoptotic Bcl-2 protein has been reported in hair follicle (HF) bulge SCs (BSCs), but its impact on SC function is unknown. Here, we show that systemic exposure of mice to the Bcl-2 antagonist ABT-199/venetoclax leads to the selective loss of suprabasal BSCs (sbBSCs), thereby disrupting cyclic HF regeneration. RNAseq analysis shows that the pro-apoptotic BH3-only proteins BIM and Bmf are upregulated in sbBSCs, explaining their addiction to Bcl-2 and the marked susceptibility to Bcl-2 antagonism. In line with these observations, conditional knockout of Bcl-2 in mouse epidermis elevates apoptosis in BSCs. In contrast, ectopic Bcl-2 expression blocks apoptosis during HF regression, resulting in the accumulation of quiescent SCs and delaying HF growth in mice. Strikingly, Bcl-2-induced changes in size and composition of the HF bulge accelerate tumour formation. Our study identifies a niche-instructive mechanism of Bcl-2-regulated apoptosis response that is required for SC homeostasis and tissue regeneration, and may suppress carcinogenesis.

Androgenetic alopecia is a common form of pattern hair loss, characterized by miniaturized hair follicles (HFs) at the front and parietal scalp, while hairs on the occipital scalp are preserved. Moreover, different body sites exhibit distinct types and patterns of HFs and understanding the molecular basis for this heterogeneity is important to design targeted treatment strategies. The Wnt signalling pathway and its Dickkopf (Dkk) inhibitors have been suggested to regulate HF type and patterning. We have previously shown that Dkk4 is specifically expressed in the epithelial placodes of HFs during mouse skin development. To elucidate the functions of Dkk4 in HF patterning, in this work, we used CRISPR/Cas9 to generate Dkk4-knockout mice. Dkk4 mutants showed disrupted HF patterning where the interplacodal distance was increased. Surprisingly, the lateral back skin of Dkk4 mutants was completely devoid of the first wave of HFs. In order to address the heterogeneity and regional differences in HF formation, we generated a Dkk4-EGFP knockin mouse line, which recapitulated the expression of Dkk4 in HF placodes. Our data revealed intra-and interplacodal differences in the expression of Dkk4-EGFP, suggesting that a WNT-DKK axis underlies the regional specificities in HF induction and patterning. Elucidating the molecular mechanisms of this heterogeneity will shed light on hair loss patterns such as in androgenetic alopecia.

Skin-derived precursor cells (SKPs) have been shown as a population of stem cells that express some markers common to the neural crest stem cells (NCSCs) as progenitor neural nestin, the low affinity neurotrophin receptor p75 and transcription factors as Sox9 and 10 and Pax3, Slug, Snail. SKPs are NCSCs that persist in certain adult tissues, particularly in the skin, which can generate a large part of the peripheral nervous system, particularly sensory neurons (SN). In this study, we reported a protocol to obtain SNs from SKPs. For this, we rely on a protocol already established by Reinhardt et al. in 2013 from Embryonic stem cells (ESCs) and induced Pluripotent stem cells (iPSCs). The SKPs were induced to generate SNs by treating cells with trophic factors and / or chemicals that had previously been shown to be important for the generation of SNs: Purmorphamine, CHIR99021, BMP4 and GDNF, BDNF, NGF. We show that the differentiation of SKPs into SNs was regulated by neurogenins 1, 2 and 3. At the end of the differentiation, the protocol allowed gene transcription of BRN3A and PRDM12 (marker of pain-sensing nerve cells). Expression was from 1000 to 2500 times higher for PRDM12 and BRN3A respectively versus undifferentiated SKP. Using immunostaining we showed that 65% and 80% of cells expressed BRN3A and peripherin, marker for peripheral neurons. Furthermore, cells expressed TRPV1, PAR2, TRPA1, substance P, CGRP, H1, B3tubulin. Using calcium imaging, a proportion of cells was responding for histamine, SLIGKV (a specific agonist of PAR2), polygodial (a specific agonist of TRPA1), and capsaicin (a specific agonist of TRPV1). In conclusion, SKP are NCSC, that able to differentiate directly into functional sensory neuron.