Regulatory roles of external cholesterol in human airway epithelial mitochondrial function through STARD3 signalling

Abstract

Background Hypercholesterolemia is found in patients with chronic lung inflammation, during which airway epithelial cells play important roles in maintenance of inflammatory responses to pathogens. The present study aims at molecular mechanisms by which cholesterol changes airway epithelial sensitivity in response to smoking. Methods Human bronchial epithelial cells (HBEs) were stimulated with cigarette smoke extract (CSE) and mice were exposed to CS/lipopolysaccharide (LPS) as models in vitro and in vivo. Severe COPD patients and healthy volunteers were also enrolled and the level of cholesterol in plasma was detected by metabolomics. Filipin III and elisa kits were used to stain free cholesterol. Mitochondrial function was detected by mitotracker green, mitotracker green, and Seahorse. Mitochondrial morphology was detected by high content screening and electron microscopy. The mRNA and protein levels of mitochondrial dynamics‐related proteins were detected by RT‐qPCR and Western blot,respectively. BODIPY 493/503 was used to stain lipid droplets. Lipidomics was used to detect intracellular lipid components. The mRNA level of interleukin (IL)‐6 and IL‐8 were detected by RT‐qPCR. Results We found that the cholesterol overload was associated with chronic obstructive pulmonary disease (COPD) and airway epithelia‐driven inflammation, evidenced by hypercholesterolemia in patients with COPD and preclinical models, alteration of lipid metabolism‐associated genes in CSE‐induced airway epithelia and production of ILs. External cholesterol altered airway epithelial sensitivity of inflammation in response to CSE, through the regulation of STARD3‐MFN2 pathway, cholesterol re‐distribution, altered transport and accumulation of cholesterol, activities of lipid transport regulators and disorder of mitochondrial function and dynamics. MFN2 down‐regulation increased airway epithelial sensitivity and production of ILs after smoking, at least partially by injuring fatty acid oxidation and activating mTOR phosphorylation. Conclusions Our data provide new insights for understanding molecular mechanisms of cholesterol‐altered airway epithelial inflammation and for developing diagnostic biomarkers and therapeutic targets to improve patient outcomes.

The Relationship of Cholesterol Responses to Mitochondrial Dysfunction and Lung Inflammation in Chronic Obstructive Pulmonary Disease

“…Even with second-hand smoke, HDL cholesterol levels are lower in dyslipidemic children [ 26 ]. A recent publication demonstrated elevated plasma levels of cholesterol in COPD patients [ 27 ]. The exact mechanisms for how smoking affects the lipid profile are not understood but are postulated to be related to catecholamine release with subsequent changes in circulating free fatty acids and resultant increases in VLDL and LDL with a decrease in HDL [ 28 ].…”

“…Recently, Li et al demonstrated that immune responses in airway epithelial cells are also influenced by cholesterol [ 27 ]. They observed that cigarette smoke extract (CSE)-induced expression of IL8 and IL6 in human bronchial epithelial (HBE) cells could be reversed by either a statin (atorvastatin) or LXR agonists (T0901317 and GW3965) [ 27 ].…”

“…Recently, Li et al demonstrated that immune responses in airway epithelial cells are also influenced by cholesterol [ 27 ]. They observed that cigarette smoke extract (CSE)-induced expression of IL8 and IL6 in human bronchial epithelial (HBE) cells could be reversed by either a statin (atorvastatin) or LXR agonists (T0901317 and GW3965) [ 27 ]. Equally, they identified that the steroidogenic acute regulatory-related lipid transfer domain-3 (STARD3) was a critical player in cholesterol and cigarette smoke-induced IL6, IL8, and IL1β [ 27 ].…”

“…They observed that cigarette smoke extract (CSE)-induced expression of IL8 and IL6 in human bronchial epithelial (HBE) cells could be reversed by either a statin (atorvastatin) or LXR agonists (T0901317 and GW3965) [ 27 ]. Equally, they identified that the steroidogenic acute regulatory-related lipid transfer domain-3 (STARD3) was a critical player in cholesterol and cigarette smoke-induced IL6, IL8, and IL1β [ 27 ]. STARD3 is a sterol-binding protein that creates endoplasmic reticulum (ER)-endosome contact sites, and STARD3 can regulate cholesterol accumulation in endosomes rather than the plasma membrane [ 45 ].…”

The relationship between cholesterol metabolism and mitochondrial function in chronic obstructive pulmonary diseases

“…Our previous data demonstrated that exogenous cholesterol supplementation altered the transcriptomic profiles of CS‐stimulated bronchial epithelial cells and cholesterol homeostasis, as well as ribosome and mitochondrial function (Figure 4). 102 STARD3‐mediated mitochondrial cholesterol overload initiates mitochondrial dysfunction, including membrane potential, respiration, dynamics and morphology. The imbalance in mitochondrial dynamics altered lipid homeostasis in lung epithelial cells, probably contributing to the exacerbation of inflammation in COPD.…”