IF aged (18–24 month) female C57BL/6 mice are administered a 7-day oral pre-conditioning course of urolithin A (50 mg/kg/day by gavage) to pharmacologically reactivate PINK1/Parkin-mediated mitophagy and pre-clear accumulated dysfunctional mitochondria from the aged myocardium, immediately followed by direct intramyocardial injection of young (8–10 week) syngeneic C57BL/6-derived allogeneic skeletal muscle mitochondria (1×10^9 viable mitochondria suspended in 100 μL respiration buffer, distributed across 10 injection sites via a 28-gauge needle, delivered within 10 minutes of reperfusion onset after 45-minute LAD occlusion),

THEN the following outcomes will be observed relative to aged vehicle controls at 28 days post-injury:

• Border zone ATP content will increase ≥40% above vehicle controls at 24 hours post-reperfusion
• Infarct size (% area at risk) will be reduced ≥30%
• Left ventricular ejection fraction (LVEF) will be ≥10 percentage points higher by echocardiography at Day 28
• Exogenous mtDNA (detected via young-donor-specific mitochondrial genome markers) will remain detectable at Day 28
• TUNEL-positive cardiomyocyte apoptosis will be reduced ≥50% in the border zone at 24 hours
• These outcomes will surpass those achieved by young allogeneic mitochondria alone (without urolithin A pre-conditioning) in aged recipients,

BECAUSE the following causal chain operates:

1. Aged cardiomyocytes accumulate dysfunctional mitochondria due to impaired mitophagy, creating "organelle gridlock" — saturated lysosomal and autophagosomal pathways that reduce residual capacity for macropinosome formation and exogenous organelle processing. This stalled autophagy in the aged myocardium is characterized by lipofuscin accumulation and lysosomal dysfunction (cited in evidence base from Saito et al., Journal of Clinical Investigation, 2016, as reported in the structured literature review above).

2. Urolithin A, a natural ellagitannin metabolite, is the most potent orally bioavailable activator of PINK1/Parkin-mediated mitophagy identified to date (outside gene therapy). A 7-day pre-treatment course selectively tags and clears damaged/depolarized mitochondria bearing phospho-PINK1 on their outer membrane, physically vacating the mitochondrial quality-control throughput queue and restoring lysosomal reserve capacity in aged cardiomyocytes [SPECULATIVE: magnitude of lysosomal reserve restoration in aged myocardium has not been quantified, but the principle is supported by urolithin A's validated mitophagy induction in aged skeletal muscle].

3. With mitophagy flux restored, actin-dependent macropinocytosis capacity for exogenous organelle uptake is unblocked. The fundamental cellular uptake mechanism for exogenous mitochondria — actin-dependent macropinocytosis — is documented to be inhibited in aged cardiomyocytes due to cytoskeletal stiffening and reduced actin turnover. The pre-clearing of intracellular mitochondr...

SENS category: GlycoSENS

Key references: • doi.org/10.1038/s41598-017-17813-0] • doi.org/10.1038/s41598-017-17813-0]. • doi.org/10.1038/s41598-017-17813-0],