FRI041 Obesity-associated Diaphragm Weakness Is Not Explained By Defects At The Level Of The Contractile Apparatus

Abstract Disclosure: R. Kaul Verma: None. D. Claflin: None. C. Davis: None. K. Converso-Baran: None. D. Michele: None. S. Brooks: None. E.D. Buras: None. Respiratory muscle dysfunction contributes to obesity-associated ventilatory disorders and is epidemiologically linked with diabetes and the metabolic syndrome. Despite its clinical relevance, the pathophysiology of obesity-related respiratory muscle weakness remains unclear. We previously applied non-invasive ultrasound to show that mice subjected to a 6-month diet-induced obesity (DIO) protocol develop diaphragm motion abnormalities. Isometric contractile force—measured ex vivo on isolated diaphragm strips—also declines with 6-month high fat diet (HFD) feeding, demonstrating that overnutrition causes functional impairment intrinsic to the diaphragm muscle. Intra-diaphragmatic adipocyte number and polymerized collagen content both increase with long-term DIO; however, their occupation of muscle cross sectional area (CSA) is insufficient to quantitatively account for force generation deficits. While disruption of tissue architecture secondary to intramuscular adiposity and fibrosis might underlie diaphragm contractile dysfunction, it is also possible that obesity impairs force production in individual myofibers. The functional integrity of the contractile apparatus (ie the sarcomere) can be interrogated in single myofibers. In this approach, muscle samples are subjected to membrane permeabilization, then individual myofibers are mechanically dissected out and affixed to a force transducer apparatus in which isometric contraction is stimulated via calcium administration. An attached camera allows for measurement of fiber CSA, such that specific force (measured force per unit CSA) can be calculated. We measured isometric specific force on both diaphragm strips and permeabilized single myofiber segments isolated from mice fed control diet (CD) or HFD feeding for periods of 6 weeks or 6 months. At the 6-week time point, muscle strip specific force was indistinguishable between groups; however, at 6 months, this parameter was significantly lower in samples from HFD-fed mice—consistent with our previous findings. In contrast, specific force measurements taken from individual myofibers were equivalent between CD and HFD-fed mice at both 6-week and 6-month time points. These data demonstrate that long-term DIO is required to reduce diaphragm contractile force; and that this decline occurs at the level of the tissue rather than the single myofiber contractile apparatus. Presentation: Friday, June 16, 2023