Background: Cardiac-specific knockout of ABHD5 (ABHD5-cKO), a lipid droplet-associated protein, leads to defects in lipid utilization characterized by massive lipid accumulation, fibrosis, and reduced ejection fraction. In these mice, Nr4a1 is upregulated via the HDAC4-MEF2 axis, further exacerbating the hexosamine biosynthesis pathway through Nr4a1, leading to glucose utilization thereby, cardiac dysfunction. Thus, we aimed to determine whether cardiac-specific knockout of Nr4a1 (Nr4a1-cKO) in ABHD5-cKO mice (cDKO) rescues the cardiac phenotype.

Results: Systolic cardiac function of cDKO mice is protected compared to ABHD5-cKO mice (cDKO, EF: 59.16±12.7%, n=9, vs ABHD5 cDKO, EF: 43.64±6.2%, n=10, p<0.0001). However, an improved cardiac ejection fraction was observed only in female cDKO mice starting from 12 weeks after cre induction compared to male counterparts (cDKO female, EF: 71.28±5.39%, n=5, vs cDKO male, EF: 55.76±13.18%, n=5, p<0.0001) indicating sex-specific differences. cDKO female mice further displayed less fibrosis (Massons Trichrome stain) without change in total lipid accumulation compared to cDKO males. As analyzed by RNA sequencing, this was accompanied by profound sex-specific transcriptomic signatures with differentially upregulated genes related to energy metabolism, whereas genes correspond to inflammation pathways were downregulated. Further single-cell nuclear sequencing (snRNA) also supports less immune cell infiltration in cDKO mice. Although no major metabolic alterations (lipid and water-soluble metabolites) were observed, pro-inflammatory cytokine markers (TNF alpha, IL-1 beta, and IL-6) were significantly downregulated in cDKO compared to ABHD5 cKO mice, pointing to a potential causative link underlying meta-inflammation.

Conclusion: This study provides evidence that Nr4a1 mediates sex-specific pro-inflammatory responses that trigger cardiac dysfunction. Our data reveal that not lipid accumulation per se induces cardiac dysfunction but that associated processes cause the pro-inflammatory state. In this regard, inhibition of Nr4a1 could be a new drug target to counteract cardiac dysfunction and meta-inflammation related to lipid accumulation in the heart.