Investigation of the pathomechanism of uremic cardiomyopathy and the infarctsize-limiting effect of ischemic preconditioning in a rat model of chronic kidney disease [Az urémiás kardiomiopátia és a szív iszkémiás prekondícionálhatóságának vizsgálata krónikus veseelégtelenségben patkány modellben]

Chronic kidney disease (CKD) is a public health problem affecting 1 of 10people worldwide. Interestingly, approximately 60% of patients are women in theearly stages of CKD. A common cardiovascular complication of CKD is uremiccardiomyopathy, most characterized by left ventricular hypertrophy (LVH) andfibrosis, ultimately leading to heart failure (HF). Moreover, uremiccardiomyopathy enhances the susceptibility of the heart to acute myocardialinfarction (AMI). However, the precise molecular mechanisms and the role ofsex-based differences in the development of uremic cardiomyopathy and AMI in CKDare still unclear. Therefore, novel therapeutic strategies that alleviate theseverity of uremic cardiomyopathy and AMI in CKD are urgently needed.MicroRNA-212 (miR-212) has been demonstrated previously to be a crucialregulator of pathologic LVH in pressure-overload-induced HF via regulating theforkhead box O3 (FOXO3)/calcineurin/nuclear factor of activated T-cells (NFAT)pathway. Here we aimed to investigate whether i) miR-212 and its selectedhypertrophy- and fibrosis-associated targets play a role in the development ofuremic cardiomyopathy, ii) the influence of sex on the severity of uremiccardiomyopathy and AMI, as well as the infarct size-limiting effect of ischemicpreconditioning (IPRE) in experimental CKD. CKD was induced by 5/6 nephrectomyin male and female Wistar rats. Serum and urine laboratory parameters weremeasured to verify the development of CKD 8 or 9 weeks after the operations.Transthoracic echocardiography was performed to assess cardiac function andmorphology. Cardiomyocyte hypertrophy and fibrosis were measured by histology.Left ventricular (LV) samples were collected for RT-qPCR, Western blot, andELISA measurements. The LV expressions of miR-212 and its LVH andfibrosis-associated selected targets, including FOXO3, AKT, and ERK1/2, weremeasured only in males by RT-qPCR and/or Western blot. In a subgroup of animals,hearts were perfused according to Langendorf and were subjected to 35 min globalischemia and 120 min reperfusion with or without IPRE. Then the infarct size orphosphorylated (p) and total forms of proteins related to the cardioprotectiveRISK (AKT, ERK1/2) and SAFE (STAT3) pathways were measured in the myocardialsamples by Western blot. The severity of CKD was similar in males and femalesbased on serum urea and creatinine levels. In CKD, diastolic dysfunctiondeveloped with preserved ejection fraction and increased A-type natriureticpeptide (ANP) levels in both sexes; however, males developed more severe LVHthan females. Moreover, histology showed the development of marked cardiacfibrosis only in CKD in males. The miR-212 was significantly overexpressed inthe LV samples in CKD in males. However, the LV expression of FOXO3, AMPK, andERK1/2 failed to change significantly at the mRNA or protein level.Interestingly, only the LV pAKT/AKT ratio was significantly increased in malesin CKD. Females had significantly smaller infarct sizes both in the sham and CKDgroups compared to males. In both sexes, IPRE significantly decreased theinfarct size in both the sham-operated and CKD groups. IPRE significantlyincreased the pSTAT3/STAT3 ratio in sham-operated but not in CKD animals in bothsexes. The groups had no significant differences in pAKT/AKT and pERK1/2 /ERK1/2 ratios. In summary, cardiac overexpression of miR-212 in CKD failed toaffect its previously implicated hypertrophy- and fibrosis-associated downstreamtargets in males. Thus, the molecular mechanism of the development of LVH in CKDseems to be independent of the FOXO3, ERK1/2, and AMPK in our model. The infarctsize-limiting effect of IPRE was preserved in both sexes in CKD despite the moresevere uremic cardiomyopathy in male CKD rats and the smaller infarct size infemales. Further research is needed to identify crucial molecular mechanisms inthe development of uremic cardiomyopathy and the cardioprotective effects ofIPRE in CKD.