Abstract 555: Sex-Dependent Regulation of Cardiomyocyte Function by Midkine in Pediatric Dilated Cardiomyopathy

Abstract

Background: Pediatric dilated cardiomyopathy (DCM) is a disease with a poor prognosis that affects 1 in 100,000 children. Girls with DCM have worse outcomes than boys, and the mechanisms that lead to these differences are not clear. We have identified a cytokine, midkine (MDK) that is significantly upregulated in the serum from pediatric DCM patients. Circulating MDK is significantly higher in girls with DCM requiring heart transplantation compared to girls with DCM who are stable. Objective: The objective of this study is to determine if MDK impacts cardiomyocyte function in a sex-specific manner in juvenile male and female cells. Methods: Cardiomyocytes isolated from 3 week old juvenile male and female rats (JRVMs) were treated with 1μg MDK for 48 hours. Cardiomyocyte function and calcium dynamics were assessed using an IonOptix system. Myofibril mechanics and calcium sensitivity were measured. In addition, RNA sequencing was completed to identify differentially regulated pathways in juvenile male and female cardiomyocytes in response to MDK. Results: Female JRVMs treated with MDK had higher peak calcium and slower calcium reuptake compared to vehicle-treated female JRVMs. In contrast, male JRVMs treated with MDK did not demonstrate a change in peak calcium and had faster calcium reuptake compared to vehicle-treated male JRVMs. Myofibril calcium sensitivity was decreased in female JRVMs in response to MDK whereas calcium sensitivity was unchanged in male MDK-treated JRVMs. Analysis of the genes that were differentially expressed in cardiomyocytes in response to MDK demonstrated a sex-dependent regulation. Specifically, pathways which regulate calcium handling were only altered in female JRVMs treated with MDK but not in MDK-treated male JRVMs. Conclusions: This study demonstrates sex-specific differences in cardiomyocyte function in response to MDK. Particularly, female cardiomyocytes respond to MDK by regulating genes involved in calcium handling pathways. This suggests that elevated circulating MDK in pediatric DCM patients may lead to different cardiac responses in male and female patients. Therefore, elucidating these sex-specific disease mechanisms is critical to define therapies focused on male and female pediatric DCM patients.