The dermal sheath (DS) is a population of mesenchyme-derived skin cells with emerging importance for skin homeostasis. The DS includes hair follicle dermal stem cells, which exhibit self-renewal and serve as bipotent progenitors of dermal papilla (DP) cells and DS cells. Upon aging, stem cells exhibit deficiencies in self-renewal and their number is reduced. While the DS of mice has been examined in considerable detail, our knowledge of the human DS, the pathways contributing to its self-renewal and differentiation capacity and potential paracrine effects important for tissue regeneration and aging is very limited. Using single-cell RNA sequencing of human skin biopsies from donors of different ages we have now analyzed the transcriptome of 72,048 cells, including 50,149 fibroblasts. Our results show that DS cells that exhibit stem cell characteristics were lost upon aging. We further show that HES1, COL11A1, MYL4 and CTNNB1 regulate DS stem cell characteristics. Finally, the DS secreted protein Activin A showed paracrine effects on keratinocytes and dermal fibroblasts, promoting proliferation, epidermal thickness and pro-collagen production. Our work provides a detailed description of human DS identity on the single-cell level, its loss upon aging, its stem cell characteristics and its contribution to a juvenile skin phenotype.
Knockdown of the gene encoding transmembrane 6 superfamily member 2 protein (TM6SF2) in mice increases hepatocellular lipid content (HCL) and decreases very low-density lipoprotein secretion. Humans with TM6SF2 mutations are at higher risk of nonalcoholic fatty liver disease, but lower risk of cardiovascular disease. The relevance of TM6SF2 mutations for HCL and insulin sensitivity in type 2 diabetes is less clear. This study aimed at elucidating the relevance of the E167K (SNP rs58542926) mutation in the gene encoding TM6SF2 for HCL, hepatic insulin sensitivity and whole-body insulin sensitivity in type 2 diabetes.
We compared male patients with recently diagnosed type 2 diabetes with (n=16) or without (n=16) E167K mutation, matched for age and BMI (50±1 vs. 48±3 years; 32±1 vs. 32±2 kg/m2) from the German Diabetes Study. Whole-body and hepatic insulin sensitivity were assessed by Botnia-clamp tests with [6,6-2H2]glucose, HCL by 1H magnetic resonance spectroscopy and hepatic fibrosis by the fibrosis-4 index (FIB4).
Patients with and without TM6SF2 mutation had comparable levels of HbA1c (6.2±0.2 vs. 5.9±0.1%) and serum triglycerides (136±14 vs. 149±14 mg/dl). Carriers of TM6SF2 mutation had higher HCL (9.0±1.9 vs. 4.6±0.4%, p<0.05) and whole-body insulin sensitivity (7.1±0.6 vs. 5.4±0.2 mg/(kg*min), p<0.05), but similar hepatic insulin sensitivity (1.6±0.1 vs. 1.6±0.1 mg/(kg*min)) and fibrosis score (1.2±0.1 vs. 1.0±0.1).
In conclusion, the E167K mutation of the TM6SF2 gene dissociates liver steatosis from whole-body insulin sensitivity. This may result from favored trapping of triglycerides within the liver, which would in turn protect peripheral tissues from insulin resistance induced by liver-derived lipids.
Disclosure
K. Bodis: None. J. Szendroedi: None. J.M. Ahlers: None. Y. Karusheva: None. O.P. Zaharia: None. S. Antoniou: None. B. Knebel: None. Y. Kupriyanova: None. J. Hwang: None. V. Burkart: None. K. Muessig: None. H. Al-Hasani: None. M. Roden: Advisory Panel; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Poxel SA, Servier. Board Member; Self; Eli Lilly and Company. Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Sanofi. Speaker's Bureau; Self; Novo Nordisk Inc. D.F. Markgraf: Research Support; Self; Sanofi.
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