123 Impact of local iron overload on crosstalk and phenotypes of immune and tissue cells in skin

Abstract

This project focuses on elucidating the pathogenic effects of iron overload due to erythrocyte extravasation in the skin on the immune-tissue cell crosstalk leading to lipodermatosclerosis and leg ulcer in patients with chronic venous insufficiency. We generated a new mice model with local iron-overload in the skin, via ID-injection of iron-dextran (Fedx). Prussian blue staining proved that iron accumulates in the dermis and in the dWAT of these mice, like in patients’ skin. Skin of Fedx mice shows signs of lipodermatosclerosis; an increase of total cell count (p=0.001) in the dermal layer, particularly of F4/80+ macrophages (p=0.019) and PDGFRa+ fibroblasts (p<0.001), accompanied with less collagen in the deeper dermis and a reduction in the size of the dWAT (p<0.001) and of the adipocytes (p<0.001). Microscopic and gene expression analysis highlight lipolysis, the consequent reduction of lipids droplets (p=0.04), and loss of plin-1 (p=0.004) on adipocytes membrane, associated with downregulation of pro-adipogenic genes in the dWAT of Fedx mice. FACS analysis reveals a shift in F4/80+ Macrophage subtypes with the induction of TNFa (p=0.0163) and reduction of CD301b and Relm-a (both p<0.001). Upregulation of CCL2 (p=0.02), IL1ß, HMOX-1 (p=0.0001 dermis, p=0.01 dWAT) and CCR2 (p=0.01) genes, indicate for a pro-inflammatory activation in the dermal compartment. Mechanistic analysis with human cells in vitro shows that erythrocyte-uptake induces ROS and a pro-inflammatory phenotype in Macrophages. Fibroblasts in response to erythrocyte-fed macrophages resemble those phenotypes found in Fedx mice. The impact of erythrocytes on the differentiation and activation of adipocytes and their crosstalk to Macrophages and Fibroblasts is ongoing. Our data suggest that local iron-overload causes a complex skin phenotype with a maintained inflammatory status in the dermis, proliferative and less fibrogenic fibroblasts, impaired adipogenesis, and increased lipolysis.