Defining the role of RhoE/RND3 signalling in the control of skin homeostasis

Abstract

Dermatofibromas are benign skin growths that can occur at any site on the body and are characterised by increased levels of extracellular matrix (ECM) proteins. Most dermatofibromas are solitary and sporadic; a few are multiple and familial. Despite affecting ~3% of the population in the UK, the mechanisms that lead to these growths are currently unknown. Using exome sequencing, we have recently identified a novel heterozygous mutation (p.Thr231Met) in patients with autosomal dominant multiple familial dermatofibromas within RND3 that encodes for the GTPase protein RhoE. Mutations in RhoE protein have not been previously reported in any human disease. Moreover, the potential involvement of RhoE in the development of fibrosis has not been previously proposed. The aim of this study was to determine role of RhoE in controlling human dermal fibroblast growth and collagen synthesis and define whether RhoE may act as a key mechanosensing molecule to regulate fibroblast phenotype under homeostatic conditions.

Data has revealed that loss of RhoE, or expression of RhoE T231M mutation results in increased adhesion of fibroblasts to ECM and this is coupled with increased activation of b1 integrins that form the main link between the cell and matrix. Loss of RhoE also increases synthesis of Collagen XII and results in less organised ECM produced by these fibroblasts. We have shown that the enzyme PLOD2 that cross-links collagen is a novel binding partner for RhoE and the RhoE T231M mutation disrupts this complex. Mechanistically, PLOD2 depletion leads to reduced b1 integrin activity, reduced expression of Collagen XII and increased alignment of ECM proteins. Moreover, PLOD2 depletion restored b1 integrin activity and ECM alignment in RhoE knockout cells, suggesting the RhoE-PLOD2 complex plays a key role in adhesion and ECM organisation. Finally, analysis of patient-derived tissues demonstrated increased levels of PLOD2 and reduced RhoE expression in the dermis in dermatofibroma samples compared to normal skin. Our data suggests that RhoE may play a role in controlling PLOD2 function and may contribute to control of dermal homeostasis. Data arising from this study sheds new light on the role of RhoE in regulating dermal fibroblast function and offer potential insight into new mechanisms leading to fibrosis.

Date of Award	1 Jul 2022
Original language	English
Awarding Institution	King's College London
Supervisor	Madeline Parsons (Supervisor) & Tanya Shaw (Supervisor)