Deletion of Cd248 in <i>Postn</i> <sup>+</sup> myofibroblast fails to attenuate pressure-overload induced cardiac remodeling and fibrosis in mice

Cardiac fibrosis driven by activated myofibroblasts is a central feature of pressure-overload heart disease. CD248 (Endosialin/TEM1) has been implicated as a pro-fibrotic marker in ischemic cardiac injury, but its role in pressure overload remains unclear. Here, we tested whether selective deletion of Cd248 in Periostin-expressing (<i>Postn</i> ^<i>+</i> ) myofibroblasts mitigates pressure-overload cardiomyopathy induced by transverse aortic constriction (TAC). We generated inducible PostnMCM^+/-;Cd248^fl/fl mice and validated tamoxifen-driven recombination specifically in <i>Postn</i> ^<i>+</i> interstitial cells. <i>In vitro</i>, Cd248 knockdown in primary adult mouse cardiac fibroblasts reduced TGF-β1-induced migration and the expression of actomyosin contractile markers; however, it notably failed to suppress the expression of key matrix genes (<i>Col1a1</i>, <i>Postn</i>), indicating a molecular uncoupling of cytoskeletal dynamics from collagen synthesis. Consistent with this, Postn-restricted Cd248 deletion in vivo produced no significant differences in survival, echocardiographic indices, histological fibrosis, or cardiomyocyte hypertrophy compared to controls at 8 weeks post-TAC. Furthermore, while <i>Cd248</i> ^<i>+</i> fibroblasts in the TAC model were enriched for chemotactic signaling programs, immune cell infiltration remained negligible, rendering this immunomodulatory function redundant. These data indicate that while CD248 regulates fibroblast cytoskeletal dynamics <i>in vitro</i>, it is dispensable for matrix production and fibrosis in vivo during pressure overload. Our results highlight the profound context-dependence of CD248 as an anti-fibrotic target.<h4>etoc blurb</h4>In pressure‑overloaded mouse hearts, deleting <i>Cd248</i> specifically in <i>Postn</i> ⁺ myofibroblasts fails to improve cardiac remodeling or fibrosis, despite clear cell-autonomous effects on cultured primary cardiac fibroblast migration and activation <i>in vitro</i>. Single‑cell and transcriptomic analyses reveal that while CD248 regulates actomyosin-related cytoskeletal dynamics, it is dispensable for extracellular matrix production in this specific hemodynamic context. These findings highlight the profound context‑dependent efficacy of CD248‑targeted antifibrotic strategies across different etiologies of heart disease.