IF a sequentially-phased triple-combination regimen of Urolithin A (50 mg/kg/day, oral gavage, weeks 1–8), AICAR (500 mg/kg/day, intraperitoneal injection, weeks 3–8), and GW501516 (5 mg/kg/day, oral gavage, weeks 3–8) — with urolithin A administered as a two-week mitophagy primer before the biogenesis-driving mimetics are introduced — is administered to frail, exercise-intolerant 24-month-old male C57BL/6J mice (confirmed frail by Frailty Index ≥ 0.45 and grip-strength < 20th percentile for age-matched cohort),

THEN compared to vehicle control, age-matched voluntary wheel runners, and non-sequenced simultaneous triple-combination controls, the sequenced regimen will produce: (1) ≥40% reduction in skeletal muscle mtDNA deletion heteroplasmy (gastrocnemius, measured by long-range PCR and digital droplet PCR), (2) ≥35% increase in mtDNA copy number normalized to nuclear DNA (COX2/β-globin ratio, qPCR), (3) ≥2-fold increase in PINK1 and LC3-II protein in muscle relative to vehicle control (Western blot), (4) ≥25% increase in Pax7⁺/MyoD⁺ co-positive satellite cells per fiber cross-section (immunofluorescence, tibialis anterior), (5) ≥20% improvement in grip strength and rotarod latency-to-fall relative to vehicle control, measured at week 8 endpoint, and these outcomes will exceed those of simultaneously-dosed triple-combination controls by ≥15%, demonstrating that sequence—not merely pharmacological co-presence—is mechanistically critical,

BECAUSE the following causal chain is proposed:

1. Mitophagy priming clears the substrate before biogenesis replenishes it. Urolithin A, a gut-derived ellagitannin metabolite, activates the PINK1/Parkin pathway, selectively tagging depolarized mitochondria with ubiquitin chains for p62/LC3-II–mediated lysosomal degradation. In aged muscle, these depolarized organelles are the primary repository of clonally-expanded mtDNA deletions. By administering UA before biogenesis stimulation, the pool of damaged mitochondrial templates is actively cleared prior to replication, reducing the probability that new daughter mitochondria inherit deletion-carrying genomes. [Source: Evidence Set narrative — Urolithin A section, PINK1/Parkin mechanism; no DOI available in Evidence Set]

2. AMPK activation drives PGC-1α/TFAM-mediated mitochondrial biogenesis into a cleared niche. Once the deletion-harboring mitochondria have been degraded (weeks 1–2), AICAR-mediated AMPK phosphorylation of PGC-1α (Ser-177) during weeks 3–8 induces transcription of TFAM and NRF1/NRF2, driving replication of the remaining wild-type mtDNA genomes and biogenesis of structurally intact, high-membrane-potential mitochondria. Because the mutant template pool was pre-reduced by UA-driven mitophagy, newly synthesized mtDNA has a higher probability of originating from wild-type copies, shifting heteroplasmy toward wild-type. [Source: Evidence Set narrative — AICAR/AMPK section; no DOI available in Evidence Set]

3. **PPARδ activation remodels fiber...

SENS category: RepleniSENS