NRF2 Shortage in Human Skin Fibroblasts Dysregulates Matrisome Gene Expression and Affects Collagen Fibrillogenesis

NRF2 is a master regulator of the antioxidative response that was recently proposed as a potential regulator of extracellular matrix (ECM) gene expression. Fibroblasts are major ECM producers in all connective tissues, including the dermis. A better understanding of NRF2-mediated ECM regulation in skin fibroblasts is thus of great interest for skin homeostasis maintenance and aging protection. In this study, we investigate the impact of NRF2 downregulation on matrisome gene expression and ECM deposits in human primary dermal fibroblasts. RNA-sequencing‒based transcriptome analysis of NRF2 silenced dermal fibroblasts shows that ECM genes are the most regulated gene sets, highlighting the relevance of the NRF2-mediated matrisome program in these cells. Using complementary light and electron microscopy methods, we show that NRF2 deprivation in dermal fibroblasts results in reduced collagen I biosynthesis and impacts collagen fibril deposition. Moreover, we identify ZNF469, a putative transcriptional regulator of collagen biosynthesis, as a target of NRF2. Both ZNF469 silenced fibroblasts and fibroblasts derived from Brittle Corneal Syndrome patients carrying variants in ZNF469 gene show reduced collagen I gene expression. Our study shows that NRF2 orchestrates matrisome expression in human skin fibroblasts through direct or indirect transcriptional mechanisms that could be prioritized to target dermal ECM homeostasis in health and disease.

Filaggrin and filaggrin 2 processing are linked together through skin aspartic acid protease activation

Skin aspartic acid protease (SASPase) is believed to be a key enzyme involved in filaggrin processing during epidermal terminal differentiation. Since little is known about the regulation of SASPase function, the aim of this study was to identify involved protein partners in the process. Yeast two hybrid analyses using SASPase as bait against a human reconstructed skin library identified that the N-terminal domain of filaggrin 2 binds to the N-terminal fragment of SASPase. This interaction was confirmed in reciprocal yeast two hybrid screens and by Surface Plasmon Resonance analyses. Immunohistochemical studies in human skin, using specific antibodies to SASPase and the N-terminal domain of filaggrin 2, showed that the two proteins partially co-localized to the stratum granulosum. In vitro enzymatic assays showed that the N-terminal domain of filaggrin 2 enhanced the autoactivation of SASPase to its 14 kDa active form. Taken together, the data suggest that the N-terminal domain of filaggrin 2 regulates the activation of SASPase that may be a key event upstream of filaggrin processing to natural moisturizing factors in the human epidermis.