Obesity is a risk factor for cardiovascular disease. C1q/tumor necrosis factor-related protein 9 (CTRP9) is an adipokine that is downregulated by obesity. We investigated the role of CTRP9 in cardiac injury with loss-of-function genetic manipulations and defined the receptor-mediated signaling pathway downstream of this adipokine. CTRP9-knockout (CTRP9-KO) mice at the age of 12 weeks were indistinguishable from wild-type (WT) mice under basal conditions. CTRP9-KO mice had exacerbated contractile left ventricle dysfunction following intraperitoneal injection of lipopolysaccharide (LPS) compared to WT mice. Administration of LPS to CTRP9-KO mice also resulted in increased expression of proinflammatory cytokines and oxidative stress markers in the heart compared to WT mice. Likewise, CTRP9-KO mice showed increased myocardial infarct size and elevated expression of inflammatory mediators in ischemic heart following ischemia and reperfusion compared to WT mice. Treatment of cardiac myocytes with CTRP9 protein led to suppression of LPS-induced expression of proinflammatory genes, which was reversed by blockade of AMPK or ablation of adiponectin receptor I (AdipoR1). Systemic delivery of CTRP9 attenuated LPS-induced cardiac dysfunction in WT mice but not in muscle-specific transgenic mice expressing dominant-negative mutant form of AMPK or in AdipoR1-knockout mice. CTRP9 protects against acute cardiac damage in response to pathological stimuli by suppressing inflammatory reactions through AdipoR1/ AMPK-dependent mechanisms.O besity causes the progression of various cardiovascular disorders, including ischemic heart disease (1, 2). Adipose tissue functions as an endocrine organ by producing various bioactive secreted proteins, also known as adipokines, that can directly affect the nearby or remote tissues (3). Most adipokines promote obese complications with proinflammatory properties. In contrast, a few numbers of adipokines such as adiponectin are downregulated in obese states, and these factors typically exert salutary actions on obesity-linked cardiovascular disorders (3, 4).C1q/tumor necrosis factor-related protein families (CTRPs) are conserved paralogs of adiponectin that contain collagen-like and globular C1q-like domains (5). CTRP9 has the highest amino acid identity to adiponectin among CTRPs (6). Like adiponectin, CTRP9 is abundantly expressed in adipose tissue. Plasma CTRP9 levels are reduced in diet-induced or leptin-deficient obese mice (6). Clinically, CTRP9 levels associate negatively with visceral fat adiposity and positively with favorable glucose or metabolic phenotypes (7).Several experimental studies demonstrated that CTRP9 acts as an adipokine that modulates metabolic and cardiovascular function. Systemic delivery of CTRP9 lowers glucose levels in obese mice (6). Transgenic overexpression of CTRP9 is protective against diet-induced obesity and glucose intolerance (8), whereas CTRP9-deficiency exacerbates insulin resistance and hepatic steatosis (9). These results suggest that CTRP9 plays a physiolo...