Exploring Mechanical Niches Identified by Hair Follicle Compression and How These Transduce Proliferation and Differentiation Cues in Epidermally Derived cells.

Abstract

In this study the hair follicle structure and surrounding tissue was investigated before, during and after the shaving process in order to better characterise the hair follicle hysteresis (lag in response) observed during the shaving process. Individual hair shafts were loaded with weights designed to mimic the forces generated during the shaving process and deformations in nuclear morphology were used as an indicator of force transduction. Upon identifying distinct mechanical compartments corresponding to regions consistent with the infundibulum, isthmus and suprabulbar regions the study then focussed on elucidating how dermal collagen may facilitate this. Multiphoton microscopy was utilised to interrogate the extrafollicular collagen and the subsequent images were analysed to reveal distinct differences in collagen bundling at the infundibulum, isthmus and suprabulbar regions. To model how heterogeneities in collagen bundling could impact upon epidermal and follicle homeostasis collagen hydrogels were constructed and characterised. Assessment of involucrin and Ki67 levels in HaCaT cells by confocal microscopy revealed elevated proliferation rates in cells on high density (HD) matrices compared with those on low density (LD) matrices which also correlated with increased nuclear volume. HD matrices have smaller collagen bundles and therefor represent a less stiff matrix compared with the low density LD matrices. ERK1/2, JNK and p38 MAPKs have been well reported as effectors on keratinocyte proliferation and differentiation rates in response to mechanical cues and so inhibitors of each were used to identify if these MAPKs were also important in transducing matrix density/stiffness cues that impact upon proliferation and differentiation rates. P38, ERK1/2 and JNK were all found to be important in mediating the proliferation advantage derived from the HD matrices, with JNK being a potential candidate in linking nuclear dynamics with collagen density-mediated proliferation and differentiation rates. JNK was further demonstrated as being the dominant player in transducing the proliferation advantage conferred by the HD matrix.