Removal of the WD Domain of Atg16l1 Required for LC3 Associated Phagocytosis is not required for preserving skin homeostasis in mice
The skin is a multifunctional organ, forming a barrier between the external and internal environment, thereby functioning as an initial safeguard against foreign and harmful environmental and biological factors. The barrier function is governed by the epidermis, a stratified epithelium composed of an outermost cornified envelope, several differentiated layers, and an innermost basal layer, anchored to the basement membrane (BM). Below the BM lies the dermis, which is composed of an extracellular matrix (ECM), formed by the dermal fibroblasts and dermal adipose tissue. The skin is subject to constant cellular turnover (terminal differentiation) that maintains the homeostatic state of the skin. Recently, autophagy has been implicated in epidermal differentiation and in preserving homeostasis in the skin. The AKT/mTORC1 pathway is a key regulator for epidermal development and differentiation, and conditions (e.g., psoriasis) are linked to the hyperactivation of these key autophagy regulators. A further process known as LC3-associated phagocytosis (LAP) uses some but not all components of autophagy. The Atg16l1 E230 mouse model (E230), deficient for LAP, has been widely used to study the effects of LAP-deficiency and autophagy in tissue homeostasis. Here, the E230 model was used to study the relationship between skin homeostasis and LAP and to determine whether LAP-deficient mice (WD) display a cutaneous skin phenotype. Histological analysis of male 1-year-old Wild Type (WT) and WD mice skin revealed morphological differences in dorsal and tail skin. qPCR analysis of key keratins showed no differences (p > 0.05) when compared between genotypes. This was confirmed by western blotting studies. In addition, the expression of general proliferation markers (Akt & ERK2) showed a small reduction (p < 0.05) in the WD mice skin. General skin barrier formation was assessed by dye permeation assays, which demonstrated full and proper formation of the skin barrier at E18.5 in both WT and WD. Notable dermal thinning in the WD mice skin (p < 0.0001), led us to examine the biomechanical properties to dismiss any abnormalities relating to biomechanical functionality. Results indicate that WT and WD mouse skin show identical biomechanical properties at these ages (p < 0.05 and p < 0.01, respectively). In summary, the noted differences in the dermal and epidermal histology of WD skin were shown to be functionally insignificant in terms of epidermal permeability and dermal biomechanics.