Extracellular release of damaged mitochondria induced by cytotoxic conditioning exacerbates GVHD

Abstract

Abstract:Despite therapeutic advancements, graft versus host disease (GVHD) is a major complication of hematopoietic stem cell transplantation (HSCT). Pathogen and damage associated molecular patterns released following pre-transplant conditioning play an important role in the initiation of GVHD. However, the role of extracellular mitochondria as an endogenous danger signal has not been fully explored. Herein, we report that cytotoxic conditioning with radiation leads to mitochondrial fission and dysfunction and impaired induction of PINK-1/PARKIN-dependent mitophagy, specifically in the intestinal mucosal layer. This radiation-induced imbalance in mitochondrial dynamics leads to the expulsion of mitochondria from intestinal epithelial cells in a cell-death independent manner bothin vitroin cell culture supernatants of the Caco-2 cell line andin vivoin plasma of BALB/c mice. Extracellular mitochondria released upon irradiation were damaged, with functional impairment in ATP production and, increased protein carbonylation. Transplantation of isolated damaged mitochondria along with HSCT and splenocytes in a C57BL6/J ➔ BALB/c mouse model of GVHD aggravated the disease-induced mortality. In mixed lymphocyte reactions, pre-incubation of BALB/c stimulator cells with syngeneic extracellular mitochondria increased the activation and proliferation of C57BL6/J responder T cells. In a cohort of pediatric patients who underwent HSCT, fractionated irradiation given with their conditioning regimen increased the abundance of circulating extracellular mitochondria and correlated with the incidence of GVHD. Our results suggest that modulation of extracellular mitochondria could be a novel therapeutic target to prevent GVHD after HSCT.