Sex-stratified piRNA expression analysis reveals shared functional impacts of perinatal lead (Pb) exposure in murine hearts

The landscape of PIWI-interacting RNA (piRNA) expression in the heart is poorly understood, particularly regarding sex differences. Altered piRNA expression has been reported in cardiovascular disease (CVD), and although exposure to the metal lead (Pb) is strongly associated with CVD risk, no studies have investigated Pb's effects on cardiac piRNAs. This study aimed to characterize piRNA expression in the murine heart and assess sex-specific effects of human-relevant maternal Pb exposure on adult offspring cardiac piRNA expression. piRNAs were identified from whole mouse hearts using sodium periodate exclusion of small RNA and subsequent sequencing. Control mice expressed 18,956 piRNAs in combined-sex analysis; sex-specific analyses revealed 9,231 piRNAs in female hearts and 5,972 piRNAs in male hearts. Genomic mapping showed 28-41% aligned to introns, while 12-28% mapped to exons. Comparing control and Pb-exposed hearts, we found more potential Pb-induced expression changes in females (847) compared to males (187) (p-value < 0.05 and |logFC| > 1). These piRNAs were significantly enriched near genes involved in biological processes related to heart function and CVD development, including mitochondrial function, energy metabolism, and cardiac muscle structure (FDR < 0.05). Overall, we characterized combined and sex-stratified piRNA expression in both control and Pb-exposed murine hearts. In addition to providing a foundation for sex-specific piRNA expression in the heart, these findings suggest a novel epigenetic mechanism by which developmental Pb exposure may impact CVD risk later in life. Future studies will link these sex-specific molecular changes to Pb-induced alterations in cardiac function.