Palmitate lipotoxicity in enteric glial cells: Lipid remodeling and mitochondrial ROS are responsible for cyt c release outside mitochondria

Enteric glial cells (EGCs) are components of the enteric nervous system, an organized structure that controls gutfunctions. EGCs may be vulnerable to different agents, such as bacterial infections that could alter the intestinalepithelial barrier, allowing bacterial toxins and/or other agents possessing intrinsic toxic effect to access cells.Palmitate, known to exhibit lipotoxicity, is released in the gut during the digestion process. In this study, weinvestigated the lipotoxic effect of palmitate in cultured EGCs, with particular emphasis on palmitate-dependentintracellular lipid remodeling. Palmitate but not linoleate altered mitochondrial and endoplasmic reticulum lipidcomposition. In particular, the levels of phosphatidic acid, key precursor of phospholipid synthesis, increased,whereas those of mitochondrial cardiolipin (CL) decreased; in parallel, phospholipid remodeling was induced.CL remodeling (chains shortening and saturation) together with palmitate-triggered mitochondrial burst, causedcytochrome c (cyt c) detachment from its CL anchor and accumulation in the intermembrane space as solublepool. Palmitate decreased mitochondrial membrane potential and ATP levels, without mPTP opening.Mitochondrial ROS permeation into the cytosol and palmitate-induced ER stress activated JNK and p38, culminatingin Bim and Bax overexpression, factors known to increase the outer mitochondrial membrane permeability.Overall, in EGCs palmitate produced weakening of cyt c-CL interactions and favoured the egress of thesoluble cyt c pool outside mitochondria to trigger caspase-3-dependent viability loss. Elucidating the mechanismsof palmitate lipotoxicity in EGCs may be relevant in gut pathological conditions occurring in vivo such asthose following an insult that may damage the intestinal epithelial barrier.