Cytokine-mediated macrophage transition promotes early cardiac fibrosis in chronic hypertension

Cardiovascular disease (CVD) remains the leading cause of death in the United States, and fibrotic remodeling is a defining feature of heart failure and many forms of CVD. While macrophages are known contributors to late-stage fibrosis, the early cellular drivers that initiate chronic fibrotic remodeling are poorly defined. Emerging evidence suggests that macrophages can undergo a macrophage-to-myofibroblast transition (MMT), positioning them as active generators of fibrosis rather than passive modulators. Here, we investigate MMT as a primary contributor to cardiac fibrosis in hypertension-induced heart failure. We hypothesize that MMT represents a key mechanistic driver of fibrotic remodeling, and this phenomenon is mechanistically highlighted by Interleukins 10 and 4 (IL-10 & IL-4) as immunological modulators. A 14-day Aldosterone + 1% high salt water mouse model of hypertension was utilized. Cardiac ultrasound was used to measure cardiac ejection fraction (EF). Direct left ventricle catheterization was used to investigate the left ventricular relaxation rate. Flow cytometry and fluorescence microscopy were used to identify MMT populations in the heart, and in vitro and primary in vitro studies were employed to delineate the mechanism of this macrophage differentiation. Cardiac ultrasound revealed no change in EF at day 14 compared to baseline; however, direct catheterization to the left ventricle at day 10 revealed significantly decreased left ventricular relaxation rate in the hearts of hypertensive mice, indicating diastolic dysfunction without impaired EF. To investigate the underlying cause of ventricular stiffness, hearts from 14-day hypertensive mice were analyzed by Picro Sirius red stain, which revealed significant interstitial fibrosis. Furthermore, fluorescence microscopy revealed a large MMT population (αSMA+CD68+), which rivaled the dedicated myofibroblast population (αSMA+CD68-). Flow cytometric analysis gave quantitative analysis and showed that MMT cells outnumbered the dedicated myofibroblast population. RAW264.7 mouse macrophage cell line and primary bone marrow-derived macrophages (BMDMs) were utilized for in vitro mechanistic studies. IL-10 media supplementation promoted MMT in a dose-dependent manner; the same result occurred in IL-4-treated cells, although to a lesser extent. Intriguingly, IL-4 treated cells began to produce IL-10 indicating a potential macrophage-specific feedback mechanism to promote MMT. A large MMT population was identified by both flow cytometry and fluorescence imaging and posed a significant proportion of αSMA+ myofibroblast-like cells. Furthermore, our in vivo analyses and collagen staining were consistent with an early hypertensive heart failure-like phenotype, implicating MMT as a component of fibrotic remodeling in hypertension. Finally, in vitro studies in both RAW264.7 and primary BMDMs highlighted the roles of IL-10 and IL-4 as drivers of MMT and as potential therapeutic targets in heart failure and other CVDs. Taken together, our study identified a large and previously underappreciated MMT population in the natal stage of CVD, hypertension. This population outnumbered their dedicated-myofibroblast counterparts, and analyses of MMT cells revealed enhanced collagen 1 and αSMA expressions, a phenotype currently being interrogated for pathogenicity. Future work will focus on the differentiation process of MMT in the context of IL-10 and IL-4 to elucidate macrophage-specific inhibitors of MMT and pathological fibrosis. Funding Sources: NIH RO1-HL146713AHA 23TPA1076467NIH R25-GM083247 This abstract was presented at the American Physiology Summit 2026 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.