Cardiomyocyte BMAL1 deficiency worsens obesity-related cardiomyopathy with heightened PINK1/Parkin-linked mitophagy and mitochondrial dysfunction

The heart has its own internal clock, and a key gear in that clock is a protein called BMAL1. This study asked what happens to the heart when BMAL1 is silenced specifically in heart muscle cells during obesity. Researchers fed mice a high-fat diet to mimic obesity-related cardiomyopathy, then compared normal mice to mice engineered to lack BMAL1 only in their cardiomyocytes. They also stressed cultured heart cells with palmitic acid, a saturated fatty acid that mimics lipid overload. When BMAL1 was absent, obese mice developed worse heart enlargement, scarring, and functional decline. At the molecular level, losing BMAL1 triggered excessive activation of a mitochondrial quality-control pathway called PINK1/Parkin-mediated mitophagy — a process that normally recycles damaged mitochondria but becomes destructive when overactivated. Mitochondria in these cells showed disrupted membrane voltage, excessive reactive oxygen species, and ultimately cell death. Conversely, boosting BMAL1 in cultured cells reversed most of these harms. The findings position BMAL1 as a guardian that keeps mitochondrial housekeeping in check under metabolic stress, and suggest that restoring circadian clock function in the heart could be a new angle for treating obesity-related heart disease.

• BMAL1 protein expression was reduced in the hearts of high-fat diet (HFD) mice compared with chow-fed controls, suggesting that obesity itself suppresses the cardiac circadian clock.
• Cardiomyocyte-specific Bmal1 knockout (Bmal1-CMKO) mice on HFD showed exacerbated myocardial hypertrophy, fibrosis, contractile impairment, and apoptosis relative to HFD mice with intact BMAL1.
• Loss of BMAL1 was associated with elevated expression of PINK1/Parkin pathway proteins and increased LC3-II levels, indicating heightened mitophagy flux under lipid stress.
• In palmitic acid-treated H9c2 cardiomyocytes, Bmal1 silencing worsened mitochondrial membrane potential loss and reactive oxygen species accumulation, while Bmal1 overexpression attenuated these effects and improved cell viability.
• Collectively, the data frame excessive PINK1/Parkin-driven mitophagy — not simply reduced mitophagy — as the proximate mitochondrial mechanism downstream of BMAL1 deficiency in obese hearts.

The study used three complementary models: (1) an in vivo HFD-induced obesity-related cardiomyopathy model in mice, with a cardiomyocyte-specific Bmal1 conditional knockout line (Bmal1-CMKO) to isolate cardiac-cell-autonomous effects; (2) an in vitro palmitic acid (PA)-treated H9c2 rat cardiomyocyte model with Bmal1 siRNA silencing or plasmid overexpression; and (3) molecular readouts including echocardiography, histology (hypertrophy/fibrosis markers), mitochondrial membrane potential assays, ROS quantification, and Western blotting for PINK1, Parkin, LC3-II, and apoptosis markers. Specific sample sizes per group and duration of HFD feeding are not stated in the abstract. The study was published in 2026 from a Chinese research group and is classified as preliminary tier owing to reliance on rodent and cell-line models without human validation.

Because all in vivo data derive from a single mouse model (HFD + cardiomyocyte Bmal1-CMKO), causality between BMAL1 loss and the PINK1/Parkin axis is correlative at the whole-organ level — a rescue experiment re-expressing BMAL1 specifically in Bmal1-CMKO hearts in vivo would strengthen the mechanistic claim. The H9c2 cell line is an embryonic rat myoblast that does not fully recapitulate adult cardiomyocyte metabolism, so findings may not translate directly to primary human cardiomyocytes or patient myocardium. The study does not resolve whether excessive mitophagy is the primary driver of dysfunction or a secondary response to upstream metabolic injury, nor does it clarify how BMAL1 transcriptionally regulates PINK1/Parkin targets. Human data linking cardiac BMAL1 levels, circadian disruption, and clinical heart failure outcomes in obesity are entirely absent and represent the critical next step.

This article extends the corpus's broader examination of mitophagy as a double-edged mechanism in tissue pathology. It directly parallels [§136], which studies PINK1/Parkin-linked mitophagy in peripheral nerve repair, demonstrating that the same pathway governs tissue fate in an organ-specific manner depending on context and magnitude of activation. It also parallels [§29] (represented in the relationship metadata as examining mitophagy in metabolic disease through a distinct, non-circadian mechanism), reinforcing that mitochondrial quality control is a convergent vulnerability across obesity-related organ dysfunction. The finding that BMAL1 restrains excessive mitophagy under lipid stress conceptually extends [§125], which addresses age-related metabolic muscle dysfunction through Ca²⁺ signaling, by suggesting that circadian-regulated mitochondrial homeostasis is a broader principle across metabolically active tissues. Unlike [§115], where mitophagy activation is protective in acute lung injury, this study positions overactivated PINK1/Parkin mitophagy as pathological — an important mechanistic contrast that underscores how disease context, chronicity, and cell type determine whether mitophagy is adaptive or destructive.

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