Cardiomyocyte‐generated Monocyte Chemoattractant Protein 1 Contributes to Cardiac Inflammation During Adverse Remodeling in Pressure Overload
Authors: Ninh Van Kim , Suetomi Takeshi , Miyamoto Shigeki , Brown Joan Heller 
Published: April 2020

Attempts to normalize cardiac function in response to stress often lead to cardiovascular diseases associated with adverse remodeling. Cardiac inflammation is a hallmark feature of adverse remodeling. Although it is established that ischemic injury induces cardiac inflammation through release of substances from dying cells, mechanisms for inflammation in the context of nonischemic injury have been elusive. Our lab has previously shown that the cardiomyocyte is the initial site of transcription of pro‐inflammatory cytokines and chemokines such as MCP‐1, IL‐6, Il‐1β and Il‐18, in response to pressure overload and that this occurs in the absence of cell death. In addition, the NLRP3 inflammasome is activated in cardiomyocytes resulting in activation of caspase‐1 and generation of active forms of Il‐1β and IL‐18. Pharmacological blockade of NFκ‐β, MCP‐1 signaling, or NLRP3 inflammasome activation resulted in decreases in cardiac macrophage accumulation, fibrosis, and dysfunction. These results suggest that cardiomyocyte‐generated inflammatory mediators play a key role in adverse cardiac remodeling in response to pressure overload. However, the extent to which cardiomyocytes contribute to immune cell recruitment and remodeling through MCP‐1 and inflammasome generated Il‐1β and IL‐18 remains elusive.

To address this question, we made cardiomyocyte‐specific MCP‐1 knockout (MCP1) mice and are currently breeding cardiac specific NLRP‐3 knockout mice. MCP1 and wildtype control (Ctl) mice were subjected to transaortic constriction (TAC) or sham surgery. Blood was collected from the mice at various timepoints and analyzed for serum amylyloid A (SAA) as a marker of systemic inflammation. At the conclusion of 3 or14 days post‐surgery, whole hearts were collected for analysis of gene expression and NLRP3 priming using qPCR. Caspase‐1 activity was used to measure NLRP3 inflammasome activation.

Pro‐inflammatory cytokines were upregulated in TAC mice versus sham controls. Inflammasome priming and activation, as measured by IL‐1β and IL‐18 gene expression and caspase‐1 activity respectively, were unaffected by cardiomyocyte‐specific MCP‐1 deletion at 3 days post‐surgery. However, both IL‐1β and IL‐18 gene expression were reduced at 14 days post‐surgery in MCP1 TAC mice compared to Ctl TAC. This coincided with a reduction of CD68+ macrophage accumulation in the myocardium suggesting that infiltrating macrophages, recruited through cardiomyocyte‐generated MCP‐1, contribute to inflammatory gene expression at this time. We are currently assessing inflammasome activation in cardiomyocytes and macrophages following TAC in Ctl and MCP1 mice. Parallel experiments using cardiomyocyte NLRP‐3 KO mice will reveal the importance of inflammasome products made in the myocyte compartment. In other studies, we are assessing the contribution of cardiomyocyte‐generated cytokines and chemokines to systemic inflammation by measuring serum amyloid A. MCP1 TAC animals displayed a reduction in SAA compared to Ctl TAC animals at 14 days post‐surgery suggesting that cardiomyocyte‐derived MCP‐1 can contribute to persistent inflammation in pressure overloaded murine hearts.

Support or Funding Information

R01HL145459‐01 (JHB, SM)

T32HL007444‐37 (RSR, JC)