Therapeutic Targeting of PPAR Signaling in Cancer Treatment-Related Lymphedema

Abstract

Lymphedema secondary to cancer treatment affects up to 1 in 5 cancer survivors. It is an irreversible late normal tissue toxicity characterized by swelling and scar formation (fibrosis) of the affected limb with physical and psychosocial health consequences for patients. Recent evidence reveals changes in peroxisome proliferator-activated receptor (PPAR) signaling as an underlying pathology of this disease. PPAR agonists have demonstrated therapeutic benefit in other fibrotic conditions; their role in lymphedema, however, remains unclear.In this study, RNA-sequencing of human and murine tissues with and without lymphedema was performed. Samples included: human lymphedema (n = 4), human normal tissue control (n = 5, matched for demographics and cancer history), murine lymphedema (n = 12), and murine control (n = 9). Pathway enrichment analysis was performed. An in vitro model of lymphedema fibrosis using cultured transforming growth factor beta (TGFβ)-stimulated fibroblasts and an in vivo model of lymphedema using a murine surgical model of tail lymphedema were utilized to evaluate the effects of PPAR agonists on gene expression and fibrotic protein expression (pro-collagen Iα1, collagen) in lymphedema compared to controls.RNA-sequencing of tissue from human and murine lymphedema and control subjects identified that suppression of PPAR signaling was a hallmark of lymphedema fibrosis on pathway enrichment analysis (FDR < 0.01). In the murine model, PPAR signaling gene expression changes co-occurred with fibrotic deposition beginning as early as two weeks after lymphedema development, and continued for at least 35 weeks. Treatment of TGFβ-stimulated fibroblasts with a PPAR agonist resulted in an increase in expression of PPAR genes and suppression of COL1α1 gene expression (n≥9 per group, q < 0.05) as well as reduction in the secretion of fibrotic proteins: pro-collagen Iα1 on ELISA (n≥8 per group, P < 0.0001) and collagen I on Western blotting. PPAR agonist treatment of the murine model of lymphedema resulted in a significant reduction in lymphedema fibrosis as measured by trichrome collagen staining (n≥4 per group, P < 0.05).These data, for the first time, demonstrated the value of upregulating PPAR signaling to treat lymphedema. For this condition, which to date, has no cure, repurposing PPAR agonists for lymphedema treatment is a highly promising therapeutic opportunity, which warrants further investigation.