Reactivation of Mthfd2 during heart failure drives cardiac remodeling

Heart failure, particularly heart failure with preserved ejection fraction (HFpEF), is a prevalent clinical syndrome with limited therapeutic options, largely due to an incomplete understanding of its pathological mechanisms. Using systems genetics in the Hybrid Mouse Diversity Panel (HMDP), comprising about 100 inbred strains, we identified methylenetetrahydrofolate dehydrogenase 2 (Mthfd2) as a potential key regulator of cardiac function. MTHFD2, a mitochondrial one-carbon metabolism enzyme, is highly expressed during development but normally silenced in adult hearts. We found that Mthfd2 is reactivated under pathological stress, where it promotes cardiac remodeling and re-engages fetal gene programs. In a mouse model of HFpEF, Mthfd2 overexpression aggravated, whereas cardiac-specific deletion protected against, diastolic dysfunction. Notably, Mthfd2 activation was detected as early as three days after HFpEF induction and drove the expression of key genes associated with hypertrophy, fibrosis, and inflammation, including Nppa, Nppb, Myc, Nfatc4, and collagen family members. This function was independent of its enzymatic activity, as catalytic mutants exerted comparable effects on cardiac function. Mechanistically, MTHFD2 translocated to the nucleus and interacted with the chromatin adaptor bromodomain-containing protein 2 (BRD2). The MTHFD2-BRD2 complex bound promoters of fetal genes, recognized acetylated histone H3 lysine 27 acetylation (H3K27ac), and promoted transcription. Pharmacological inhibition of BRD2 with BBC0403 attenuated remodeling and improved diastolic function in both progressive and established HFpEF. Consistently, the expression of MTHFD2 and related heart failure genes were elevated in human HFpEF hearts. Collectively, these findings reveal an enzyme-independent, stress-induced nuclear function of MTHFD2 in regulating pathological gene expression, delineate a genetic basis of cardiac remodeling, and highlight MTHFD2 as a promising therapeutic target for HFpEF.