Finding. Blocking histone lysine demethylases with JIB-04 can prevent and reverse hypertrophic cardiomyopathy in the classic Myh6 R403Q mouse, stop sudden death in an accelerated model, and, in MYH7 R403Q human iPSC-cardiomyocytes, put connexin-43 back on the membrane and improve mitochondrial respiration. The epigenetic drug is not only a hypertrophy cosmetic. It remakes transcription and chromatin, nominates PHF2 (KDM7C) in mouse and human HCM hearts, and leaves a durable benefit after withdrawal. The liver pays a reversible lipid price that N-acetylcysteine can blunt.
Why this paper matters
HCM therapy still orbits the sarcomere. Singh, Fan, Alzhanov and Liu ask whether the epigenetic layer is causal enough to treat. A pan-KDM inhibitor that works before disease, after disease, after you stop the drug, and in old spontaneous mice is a different claim than a transcription-factor blot. Adding iPSC-CM mitochondrial respiration and gap-junction localization pulls the story into myocyte physiology, not only nuclear marks.
PHF2 as a shared mouse/human candidate, with knockdown cutting hypertrophic, inflammatory, and fibrotic programs in the three relevant cell types, is the mechanistic handle. It is still a handle on a pan-inhibitor.
What they actually measured
JIB-04 in Myh6 R403Q/+ mice: prevention in cyclosporin A–accelerated HCM including complete SCD prevention; reversal of established disease; sustained benefit after withdrawal; improved function in aged spontaneous HCM. Bulk RNA-seq and ATAC-seq: partial restoration. Proteomics: PHF2 as candidate in mouse and human HCM. PHF2 knockdown in cardiomyocytes, macrophages, fibroblasts. Human HCM hearts: elevated JIB-04-sensitive KDMs including PHF2. MYH7 R403Q iPSC-CMs: gene normalization, Cx43 membrane restoration, improved mitochondrial respiration. Toxicity: reversible hepatomegaly with hepatic lipid; NAC co-administration mitigates liver injury without killing efficacy.
The mitochondrial number lives in the iPSC-CM system. Do not pretend the mouse heart was respirometrically rescued in this abstract.
How to read the score
Around 80. Prevention plus reversal plus SCD plus a human myocyte respiration endpoint is a lot of HCM paper. Confidence is medium because the drug is dirty and the liver signal is real. Score 80.
What to do with it
Track if you work on HCM epigenetics, myosin-mutation iPSC-CMs, or myocyte mitochondria in hypertrophy. Pull the iPSC-CM OCR and Cx43 images and the withdrawal study. Do not treat JIB-04 as a near-term human drug from this brief. The directional implication is that KDM activity sustains HCM transcriptional programs and that reversing those programs can restore myocyte mitochondrial respiration in a dish while remodeling the R403Q mouse heart.