Knock-in mouse models for the characterization of meprin metalloproteases in hyperkeratosis, inflammation and systemic sclerosis

• Applicant: Professor Dr. Christoph Becker-Pauly
• Subject Area: Dermatology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 509865529

Dysregulation of proteolytic enzymes in skin has huge impact on epidermal homeostasis, which can result in severe pathological conditions such as Netherton syndrome or fibrosis. Increased expression and activity of meprin metalloproteases has been associated with hyperproliferative diseases, inflammation and systemic sclerosis. Based on mouse models and patient data we suggest meprins as possible key regulators in the onset and progression of hyperproliferative and fibrotic disorders. Until recently, the only genetically altered mice available to study meprin activities in vivo were Mep1a-/- and Mep1b-/- mice, which are full knock-outs and thus completely lack the proteases. In these animals impaired collagen deposition in skin was observed, similar to patients suffering from Ehler’s-Danlos-syndrome. Additionally, we recently demonstrated impaired wound healing and collagen VII maturation in Mep1a-/- mice. Other studies analyzing Mep1a/b-/- single and double knock-out mice revealed alterations in cytokine levels and immunological phenotypes under diseases conditions. However, to date, not a single case of a homozygous loss-of-function mutation in humans is documented that leads to a complete loss of meprin α or meprin β activity. Therefore, we propose that suitable models to study the pathological impact of meprins are mice that allow for cell type and tissue-specific induced expression of these enzymes as observed for certain skin diseases. To achieve this, we generated tamoxifen-inducible mice and inserted the Mep1a or Mep1b cDNA, including a C-terminal HA-tag, into the Rosa26 locus of wild-type C57BL/6 mice. Crossing these mice to Cre-driver animals (Krt5- and Col1a2-CreERT2) allows for increased meprin expression in keratinocytes or fibroblast. These animals will show whether increased meprin activity will be sufficient to induce the onset of hyperkeratosis, pro-inflammatory and fibrotic diseases. We recently demonstrated the feasibility of the proposed concept by inducing meprin β expression in keratinocytes (Krt5-CreERT2) leading to decreased cell adhesion and hyperkeratosis. The observed phenotype was nicely in line with increased Mep1b expression in Fra-2tg mice, which serve as a model for psoriasis and systemic sclerosis. Based on the successful DFG-funded Project (sign removed), which was performed in collaboration with Dr. Alexander Nyström (Dermatology, Freiburg), we will use these mice for proteomic identification of putative pathological meprin substrates in vivo and provide the basis to investigate the feasibility of specific meprin inhibitors for potential therapeutic treatment of hyperkeratosis, inflammation and fibrosis.

• DFG Programme: Research Grants