Abstract
Several conditions are marked by increased susceptibility to, and enhanced severity of, bacterial infections. Alcohol use disorder, one of these conditions, is known to predispose to bacterial pneumonia by suppressing the lung's innate immune system, and more specifically by disrupting critical alveolar macrophage (AM) functions. Recently, we established that chronic ethanol consumption also perturbs surfactant lipid homeostasis in the lung and that elevated concentrations of free fatty acids contribute to blocking essential AM functions, such as agonist-induced cytokine expression. In this study, we extend these observations by showing that elevated free fatty acid levels impair metabolic responses to lipopolysaccharide (LPS) in AMs. In particular, we show that the glycolytic reprogramming characteristic of LPS-stimulated AMs is blunted by the saturated fatty acid palmitate, whereas oleate, an unsaturated fatty acid, or ethanol alone, had no effect on this adaptive metabolic response. Additionally, we found that elevated concentrations of palmitate induced mitochondrial oxidative stress and that glycolytic reprogramming and cytokine production to LPS could be partially restored in AMs by either pharmacologically blocking palmitate entry into mitochondria or administering a mitochondrial-specific antioxidant. Taken together, these findings suggest that alcohol and elevated levels of saturated fatty acids conspire to impair pulmonary innate immunity by altering metabolic responses in AMs. Additionally, our findings suggest that targeting the mechanisms involved in fatty acid metabolism can restore pulmonary immunity and possibly limit bacterial pneumonia in individuals with alcohol use disorder.