Investigating the heightened pro-fibrotic response of sarcospan-deficient hearts to isoproterenol treatment

Objective: The tetraspanin-like protein sarcospan (SSPN) is a member of the dystrophin-glycoprotein complex (DGC) and shown to be important for membrane stabilization and maintaining cellular adhesion. SSPN-deficient (SSPN-/-) mice develop significant fibrosis in response to multiple stressors including beta-adrenergic stimulation. To investigate the mechanisms contributing to the increased cardiac fibrosis in response to isoproterenol we will examine several cell types responsible for fibrotic deposition in the heart including cardiac fibroblasts and infiltrating macrophages. The response to isoproterenol is regulated by beta-adrenergic receptors that regulate the normal contractile response but also contribute to pathophysiological heart function. Immune cells such as macrophages contain beta-2 adrenergic receptors and make up most of the infiltrating immune cells in the heart in response to isoproterenol and contain beta-2 adrenergic receptors. Chronic elevation of catecholamines has been found to play a critical role in development of heart failure likely due to the increase in immune cell infiltration. Therefore, we hypothesize that deletion of SSPN, which increases the response of bone marrow-derived macrophages, may also heighten immune cell activation/infiltration in the heart in response to chronic beta-adrenergic receptor activation. Methods: Mice were subjected to chronic and acute isoproterenol treatments and hearts assessed for fibrosis and immune cell infiltration using immunofluorescence techniques to detect neutrophil (Ly-6G+ and CD11b+) and macrophage (F4/F80+) cells. Infarct-style, perivascular, and interstitial fibrotic areas in the hearts were identified using Masson’s Trichrome staining and the margins examined for the presence of immune cells. Bone marrow cells will be isolated and differentiated to macrophages using G-CSF and pre-treated with isoproterenol to determine impact on activation of type 1 interferon signaling pathways using innate immune ligands. Immunofluorescence will be utilized to determine changes in beta-2 adrenergic and SSPN expression in the stimulated BMDM. Results: SSPN-deficient hearts are more fibrotic than WT hearts in response to both acute and chronic isoproterenol infusion. After isoproterenol treatment increased cellularity is evident in SSPN-deficient hearts suggesting increased immune cell infiltration. SSPN expression has been documented on several immune cell types including BMDM and signaling pathways will be identified that are activated in response to lipopolysaccharide (LPS) and B-DNA. Conclusions: The findings from this study will determine whether SSPN plays a role in the inflammatory response of BMDM after exposure to isoproterenol. This study will demonstrate whether SSPN plays a role in immune cell recruitment and remodeling of the heart in response to chronically elevated catecholamines. Funding: FSU Funding, Florida Department of Health, James and Esther King Biomedical Research Program #21K12. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.