Knockdown of GPER in Cardiomyocytes Activates NLRP3 Pathways
Authors: Groban Leanne , Wang Hao , Sun Xuming , Ferrario Carlos M. 
Published: June 2021

IntroductionImmune activation and subsequent low‐grade inflammation have emerged as important factors in the progression of heart failure, particularly among postmenopausal women. The molecular underpinnings of this effect are not clear but might involve the loss of estrogenic control on mitochondrial reactive oxygen species (ROS), with subsequent activation of the cardiac NLRP3 inflammasome; a component of the innate immune system. We've shown that activation of the G‐protein coupled estrogen receptor (GPER), by its specific agonist G1, prevents cardiac remodeling and dysfunction from estrogen deficiency, aging and hypertension, and that genetic deactivation of cardiac GPER leads to LV dysfunction. Others report that GPER has anti‐atherogenic effects partly due to suppression of toll‐like receptors. Taken together, we hypothesize that cardiac GPER has a key role in both the maintenance of cardiac mitochondrial resilience and suppression of inflammasome activation in the female heart, and that deactivation by E2 loss unbridles vulnerabilities to aging and hemodynamic stress. To study this potential GPER‐to‐cardiac mitochondrial induced‐inflammatory interaction, we characterized changes in mitochondrial ROS and innate immunity gene transcripts in hearts from cardiomyocyte specific GPER knockout (KO) female mice and GPER‐intact wild type (WT).MethodsGPER KO and WT littermates (n=6/group, 6 months old) underwent echocardiographic evaluations prior to sacrifice. Using real‐time qPCR, HPLC‐coulometric electrochemical detection, and RT2 Profiler™ PCR Array assays, frozen cardiac tissue was processed, respectively, for measures of: 1) BNP mRNA; 2) mitochondrial resilience ‐ defined by reduced glutathione‐to‐oxidized glutathione ratios (GSH/GSSG), and mRNA levels of Sirt3 and SOD2; and 3) inflammatory transcript markers of innate immunity. Data were analyzed by Student's t‐test (significance P<0.05).ResultsAs expected, GPER knockdown resulted in 40% and 34% reductions in fractional shortening (%FS) and myocardial relaxation (e′), respectively, and a 4.5‐fold increase in BNP mRNA expression (P<0.01). Oxidative stress was increased in GPER KO, as indicated by reductions in redox status and gene transcript levels of Sirt3 and its mitochondrial deacetylation substrate SOD2 (Fig. 1). Cardiac NOD‐like receptors (NLRP3, Naip5, and NLRP5) caspase‐1, caspase‐12, IL‐18, IL‐12b, and IL‐6, were all increased by 3‐fold or more when compared to WT, and this occurred independent of changes in expression of the NF‐κB gene family (Fig. 2).ConclusionAbsence of cardiac GPER allows activation of inflammatory pathways expressing as loss of mitochondrial quality control programs, such as Sirt3 and SOD2, with subsequent increases in mitochondrial ROS in association with cardiac inflammasome activation. Given that NF‐κB expression was not affected by GPER KO, it is less likely that NRLP3 is transcriptionally regulated in this model. Future studies will determine whether GPER activation by G1 blunts the NLRP3 inflammasome through a Sirt3‐mediated mitochondrial “surveillance” mechanism to limit the progression of LV dysfunction after estrogen loss and during states of pressure overload.Support or Funding InformationNIH AG033727 (LG) NIH HL051952 (CMF and LG)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.