FRI040 Thrombospondin-1 Regulates Diaphragm Stromal Architecture And Contractile Properties In Obesity-Associated Respiratory Dysfunction
Authors: Buras Eric Dale , Verma Romil Kaul , Woo Moon-Sook , Kondisetti Sri H , Davis Carol , Claflin Dennis , Converso-Baran Kimber , Michele Daniel , Brooks Susan , Chun Tae-Hwa 
Published: October 2023

Abstract
Disclosure: E.D. Buras: None. R. Kaul Verma: None. M. Woo: None. S.H. Kondisetti: None. C. Davis: None. D. Claflin: None. K. Converso-Baran: None. D. Michele: None. S. Brooks: None. T. Chun: None.
Between 40% and 80% of obese individuals are affected by respiratory disorders. These range in severity from dyspnea on exertion, which reduces exercise tolerance, to obesity hypoventilation syndrome (OHS), which doubles 5-year mortality rate. Respiratory muscle dysfunction is a common underlying factor in these conditions and is epidemiologically linked with the metabolic syndrome and diabetes. Despite its clinical relevance, the pathophysiology of obesity-related respiratory muscle weakness is not well defined. Our previous work explored the hypothesis that anatomic remodeling and contractile dysfunction of the diaphragm are interrelated obesity complications. In mice subjected to a long-term high fat diet (HFD) time course, we observed a progressive decline in diaphragm motion (measured on ultrasound), and an endpoint reduction in isometric force generation (measured ex vivo on muscle strips). These findings demonstrated that diet-induced obesity (DIO) causes functional impairment intrinsic to the diaphragm. Intra-diaphragmatic adipocyte number and polymerized collagen content both increased with duration of HFD feeding, and quantitatively correlated with isometric force deficits. All adipocytes and many collagen-depositing cells arose from fibro-adipogenic progenitors (FAPs), an intramuscular mesenchymal stem cell population. Moreover, diaphragmatic FAPs from HFD-fed mice assumed a proliferative phenotype with increased collagen production. Thrombospondin-1 (THBS-1) is a circulating matricellular protein that increases with obesity, functions as a mesenchymal cell mitogen and has been linked to muscle injury in inflammatory myopathies. We hypothesized that THBS-1 drives FAP-mediated diaphragm remodeling and contractile dysfunction in obesity. To test this, we treated isolated mouse diaphragm FAPs with THBS-1 at concentrations seen in obese human subjects. This maneuver caused increased FAP proliferation and extracellular matrix (ECM) deposition. We next compared the effects of a 6-month DIO time course on diaphragm FAP content, tissue-level gene expression, anatomy, and physiology in wild-type (WT) and Thbs1 knockout (Thbs1-/-) mice. In WT mice, DIO caused increased FAP number (flow cytometry) and shifts toward pro-fibrotic sub-types (single cell RNA-seq). These changes did not occur in Thbs1-/- mice despite similar weight gain. Thbs1-/- diaphragms also had fewer adipocytes and reduced gene/ protein levels of ECM species. Finally, diaphragm contractile force and motion parameters (excursion amplitude, inspiratory velocity, and expiratory velocity) declined with duration of obesity in WT mice, but, remained unchanged in Thbs1-/- animals. These data define THBS-1 as a novel regulator of diaphragm stromal remodeling and potential therapeutic target for mitigating obesity-associated respiratory dysfunction.
Presentation: Friday, June 16, 2023