Altered age-related changes in bioenergetic properties and mitochondrial morphology in fibroblasts from sporadic amyotrophic lateral sclerosis patients

Mitochondria play a key role in aging, which is a well-established risk factor in amyotrophic lateral sclerosis (ALS). We have previously modeled metabolic dysregulation in ALS using fibroblasts isolated from sporadic ALS (SALS) and familial ALS patients. In the present study, we show that fibroblasts from SALS patients have an altered metabolic response to aging. Control fibroblasts demonstrated increased mitochondrial network complexity and spare respiratory capacity with age which was not seen in the SALS cases. SALS cases displayed an increase in uncoupled mitochondrial respiration, which was not evident in control cases. Unlike SALS cases, controls showed a decrease in glycolysis and an increase in the oxygen consumption rate/extracellular acidification rate ratio, indicating an increased reliance on mitochondrial function. Switching to a more oxidative state by removing glucose with in the culture media resulted in a loss of the mitochondrial interconnectivity and spare respiratory capacity increases observed in controls grown in glucose. Glucose removal also led to an age-independent increase in glycolysis in the SALS cases. This study is, to the best our knowledge, the first to assess the effect of aging on both mitochondrial and glycolytic function simultaneously in intact human fibroblasts and demonstrates that the SALS disease state shifts the cellular metabolic response to aging to a more glycolytic state compared with age-matched control fibroblasts. This work highlights that ALS alters the metabolic equilibrium even in peripheral tissues outside the central nervous system. Elucidating at a molecular level how this occurs and at what stage in the disease process is crucial to understanding why ALS affects cellular energy metabolism and how the disease alters the natural cellular response to aging.