Low-Protein Diet Shields the Aging Heart by Activating Cellular Cleanup Machinery
In obese middle-aged mice, reducing dietary protein—without cutting calories—reversed cardiac inflammation and remodeling via AMPK-ULK1 mitophagy.
Summary
A new study in Aging Cell shows that dietary protein restriction (DPR) — reducing protein intake without cutting total calories — protects the aging, obese heart from chronic inflammation and structural damage. In middle-aged male mice fed a high-fat diet, four months of DPR reversed heart weight gain, normalized heart failure markers, and suppressed a key inflammatory pathway called cGAS-STING that is triggered by leaky mitochondrial DNA. The protective mechanism centers on activating AMPK, which phosphorylates ULK1 to drive mitophagy — the cellular process that removes damaged mitochondria. These findings suggest that lowering dietary protein, independently of calorie restriction, may be a practical strategy for protecting cardiovascular health during aging and obesity.
Detailed Summary
Cardiovascular disease and aging intersect in a process called 'inflammaging' — a chronic, low-grade inflammatory state that accelerates cardiac decline. Calorie restriction can slow this process, but adherence is poor and its efficacy wanes when started later in life. This study investigates whether dietary protein restriction (DPR) — reducing protein content without reducing total caloric intake — can protect the aging, obese heart, and what molecular mechanisms are responsible.
Researchers used middle-aged male C57BL/6 mice with high-fat diet-induced obesity (HF group) and compared them to animals on a normal protein (NP) diet, a low-protein (LP) diet, or a high-fat plus low-protein (HF+LP) diet over four months. HF mice showed elevated heart weight and upregulated heart failure markers including Cyclin D1 and atrial natriuretic peptide (NPPA). DPR in the HF+LP group normalized these markers, attenuating cardiac hypertrophy independently of FGF21 signaling.
Unbiased RNA sequencing of left ventricular tissue revealed that HF diet broadly activated cardiac immune response and stress-sensing pathways. In contrast, HF+LP reversed these transcriptomic signatures. At the protein level, obesity activated the cGAS-STING pathway — a cytosolic DNA-sensing cascade that drives type I interferon and pro-inflammatory cytokine production. DPR suppressed cGAS-STING signaling and downstream IRF3 and IFN-γ expression in obese hearts. Critically, mitochondrial DNA (mtDNA) was elevated in the cytosolic fraction of HF hearts, and DPR significantly reduced this cytosolic mtDNA leak.
To understand why less mtDNA escapes into the cytosol under DPR, the team examined mitochondrial quality control. DPR restored mitochondrial dynamics (fission/fusion balance), enhanced mitophagy, and maintained cardiac ATP content despite reduced overall respiratory capacity. DPR also activated AMPK and increased phosphorylation of ULK1 — a canonical autophagy-initiating phosphorylation — while suppressing mTOR signaling. These findings were confirmed in cardiomyocytes: AMPK knockdown abrogated ULK1 activation and mitophagy under low amino acid conditions, confirming AMPK as the essential upstream mediator.
These findings collectively demonstrate a mechanistic chain: dietary protein restriction → AMPK activation → ULK1-driven mitophagy → clearance of damaged mitochondria → reduced cytosolic mtDNA → suppressed cGAS-STING inflammation → attenuated cardiac remodeling. The study is limited to male mice and a single obesity model, so translation to females, humans, or other metabolic contexts requires further investigation. Nevertheless, the data position DPR as a compelling, adherence-friendly nutritional strategy for preserving cardiovascular health during obesity-associated aging.
Key Findings
- HF+LP diet normalized heart weight and heart failure markers (Cyclin D1, NPPA) in obese middle-aged mice compared with HF diet alone
- DPR suppressed the cGAS-STING pathway and downstream pro-inflammatory mediators IRF3 and IFN-γ in cardiac tissue of obese mice
- Cytosolic mitochondrial DNA was elevated in HF hearts and reduced by DPR, indicating less mtDNA leakage to drive cGAS-STING activation
- DPR restored mitochondrial dynamics (fission/fusion balance) and enhanced mitophagy markers in cardiac tissue
- DPR increased AMPK-dependent ULK1 phosphorylation while suppressing mTOR signaling, promoting mitochondrial turnover
- AMPK knockdown in cardiomyocytes abrogated ULK1 activation and mitophagy under low amino acid conditions, confirming AMPK as the essential upstream effector
- DPR maintained cardiac ATP content despite reduced total mitochondrial respiratory capacity, indicating improved mitochondrial quality over quantity
Methodology
Middle-aged male C57BL/6 mice (12–16 months) were randomized to four dietary conditions — normal protein (NP), low protein (LP), high-fat (HF), and high-fat plus low protein (HF+LP) — for 4 months (n=4–15 per group depending on assay). Outcomes included cardiac histology (H&E, Picrosirius Red), transcriptomics (RNA sequencing of left ventricular tissue, n=6/group), immunoblotting for inflammatory and mitochondrial pathway proteins, cytosolic DNA fractionation with RT-PCR, mitochondrial respiration assays, and in vitro AMPK knockdown experiments in cardiomyocytes. Statistical comparisons were performed between groups with significance set at p<0.05.
Study Limitations
The study was conducted exclusively in middle-aged male mice, limiting generalizability to females and humans. Only one model of obesity (high-fat diet) was used, and the 4-month intervention window may not capture long-term effects or reflect human dietary patterns. The authors did not report specific conflicts of interest, though funding was provided by NIH (NIDDK, NIA, NIGMS) and USDA-ARS.
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