Dermal white adipose tissue regulates human hair follicle growth and cycling

UoM administered thesis: Phd

  • Authors:
  • Carina Nicu

Abstract

The human hair follicle (HF) is a dynamic mini-organ that continuously cycles through phases of growth (anagen), regression (catagen) and rest (telogen). Human hair cycling is governed by an molecular mechanisms mediated by circulatory factors, immune cells and fibroblasts. In murine studies, dermal white adipose tissue (dWAT) plays a dual role in modulating HF functions, with mature dermal adipocytes (DAs) inhibiting epithelial HF stem cell (eHFSC) function and mediating telogen maintenance via Bmps 2 and 4, whereas dermal adipose progenitor cells (APCs) stimulate eHFSCs and telogen-anagen transition via Pdgfa. Despite the wealth of knowledge surrounding murine HF-dWAT interactions, equivalent studies in the human system are currently lacking. We resort to transmission electron microscopy, microCT imaging and histology to investigate changes in perifollicular DAs between anagen and catagen stage. With the use of ex vivo organ culture of human HFs dissected vs. with surrounding dWAT we probe the effects of perifollicular dWAT upon functions. In addition, we utilise multiplex approaches such as magnetic Luminex assay to narrow down the search for candidate factors underlying HF-dWAT communication, and laser-capture microdissection, microarray and Fluidigm to study the molecular pathways affected by adipose-derived factors. Lastly, we employ recombinant human proteins and neutralizing antibodies against specific adipose-derived factors to explore their effects upon the human HF. We demonstrate that perifollicular DAs in human scalp skin show unique changes in their lipid droplet morphology, suggesting a reduction in size during anagen-catagen transition via lipolysis and lipophagy. Despite no significant differences in DA markers between anagen and catagen, perifollicular DAs display a reduced size in the bulge and sub-bulge region as opposed to the suprabulbar and bulbar regions of the HF, suggesting anatomical and functional heterogeneity. In addition, we show that human dWAT stimulates follicular pigmentation, proliferation and hair shaft elongation. Specifically, human dWAT secretes high levels of Adiponectin and hepatocyte growth factor (HGF) in culture, the latter which is a well-known mitogenic, motogenic and pro-pigmentation factor. Indeed, HGF acts in a paracrine manner within HF-dWAT co-culture to drive proliferation and hair shaft elongation, and stimulate melanin content by increasing melanocyte numbers, dendrites and Tyrosinase activity. Fluidigm analysis reveals the Wnt/β-catenin pathway as a major downstream target. Specifically, human HGF activates Wnt signalling by inhibiting SFRP1 and DKK1 and up-regulating AXIN2, LEF1 and Wnt ligands WNT10B and WNT6. Furthermore, we identify that dWAT-derived HGF also up-regulates multiple keratins within the HF matrix, suggesting a role for HGF in HF differentiation and/or inner root sheath biology. Conversely, the effects of dWAT-derived Adiponectin upon human HFs remain unclear since treating dissected and HF-dWAT co-cultures with a mixture of Adiponectin oligomers yields no changes in proliferation, pigmentation or eHFSC markers. Interestingly, neutralizing Adiponectin isoforms results in increased melanin content and Tyrosinase activity but fewer melanocytes. Altogether, the current doctoral thesis proves that human perifollicular DAs dynamically oscillate in size during human anagen-catagen transition, as well as across different compartments of the HF. Importantly, dWAT stimulates human HF growth, proliferation and pigmentation within ex vivo HF-dWAT co-culture. These effects are mediated by production of HGF which activates the Wnt/ β-catenin pathway via SFRP1 inhibition and upregulates key keratin genes within the HF matrix. In contrast, globular Adiponectin and changes in Adiponectin isoform ratios may be responsible for the contradicting effects upon the HF mediated by human dWAT-derived Adiponectin. Notably, the novel molecular mechanisms by which dWAT-derived HGF acts upon the human HF to stimulate proliferation, pigmentation and keratin biology discovered in the present doctoral thesis may one day translate into therapies for distinct forms of hair disorders.

Details

Original languageEnglish
Awarding Institution
Supervisors/Advisors
  • David Ansell (Supervisor)
  • Ralf Paus (Supervisor)
Award date1 Aug 2020