# Modification of the dermal matrix by senescence associated lipids and its functional consequence

## TL;DR

Senescent cells modify collagen in the skin with reactive lipids, causing lasting changes to skin cell behavior and aging.

## Contribution

This study reveals how senescence-associated lipids chemically modify collagen and alter skin cell function and aging.

## Key findings

- Senescent fibroblasts modify collagen via reactive lipids like HNE and OxPL.
- Modified collagen alters fibroblast and macrophage behavior, increasing inflammation and stress responses.
- Lipid-modified collagen in skin models disrupts keratinocyte differentiation and epidermal thickness.

## Abstract

Senescent dermal fibroblasts accumulate and secrete chemically reactive lipids that are components of the senescence-associated secretory phenotype (SASP). These lipids, including 4-hydroxynonenal (HNE) and reactive oxidized phospholipids (OxPL), covalently bind to and modify proteins via Schiff base formation or Michael adduction. Our study examined lipid-induced collagen modifications and their impact on skin cells to evaluate the long-term consequences of senescent cells on the tissue microenvironment. Using mass spectrometry and biochemical analyses, we identified both high and low molecular-weight modifications to collagen types I, II and IV. Collagen modified by HNE reduced fibroblast proliferation and induced stress responses. In contrast, collagen modified by OxPL provoked inflammatory signaling. Both types of modifications influenced matrix remodeling by increasing proteinase expression while reducing collagen expression. Modified collagen also elevated levels of intracellular reactive oxygen species and lipid peroxidation. Macrophages cultured on modified collagen displayed altered cytokine profiles and Toll-like receptor signaling impairment, that depended on the specific type of lipid modification. Similarly, keratinocytes exposed to modified basal lamina collagen IV showed transient stress responses, increased cytokine expression, and reduced matrix metalloproteinase expression. Furthermore, lipid-modified collagen incorporated into organotypic skin equivalents disturbed keratinocyte differentiation and elevated markers of cellular senescence. These skin models also showed reduced epidermal thickness with HNE-modified collagen and parakeratosis on OxPL-modified matrices. In conclusion, the findings suggest that SASP lipids secreted by senescent fibroblasts alter collagen structure and the fate of residing cells. The responses are likely caused by cell-associated oxidation events upon interaction of cells with a lipid-modified matrix and can be inhibited by antioxidants in macrophages. Given collagen's long half-life in tissues, these modifications may represent a persistent mechanism by which senescent cells affect the tissue microenvironment beyond the lifespan of soluble SASP factors ― thereby sustaining an aged phenotype over extended periods.

Graphic created with Procreate (Apple). Illustrative elements adapted from Servier Medical Art (https://smart.servier.com/), licensed under CC BY 4.0.Image 1

•Reactive lipid aldehydes accumulating in and secreted by senescent cells, covalently adduct to the extracellular matrix proteins collagen types I, II, and IV.•Fibroblasts cultured on lipid modified collagen display elevated levels of cytokines, altered matrix turnover and an early senescence phenotype.•Monocyte derived cells grown on modified matrix show altered expression of cyto-/chemokines, elevated senescence markers and impaired pattern recognition receptor signaling.•Organotypic skin equivalents with modified collagen display disturbed epidermal differentiation and elevated expression of senescence markers.

Reactive lipid aldehydes accumulating in and secreted by senescent cells, covalently adduct to the extracellular matrix proteins collagen types I, II, and IV.

Fibroblasts cultured on lipid modified collagen display elevated levels of cytokines, altered matrix turnover and an early senescence phenotype.

Monocyte derived cells grown on modified matrix show altered expression of cyto-/chemokines, elevated senescence markers and impaired pattern recognition receptor signaling.

Organotypic skin equivalents with modified collagen display disturbed epidermal differentiation and elevated expression of senescence markers.