Impact of aging and caloric restriction on markers of mitochondrial dynamics, biogenesis, mitophagy, and autophagy in multiple metabolically active tissues

Aging leads to functional decline in metabolically active tissues, including the liver, heart, and skeletal muscle. Caloric restriction (CR) extends lifespan and healthspan in rodents, potentially through improved mitochondrial quality control, and enhanced autophagy. Yet, multi-tissue assessments of how aging and CR remodel mitochondrial content, dynamics, biogenesis, mitophagy, and autophagy remain limited. We quantified markers of mitochondrial content (TOM20, citrate synthase), biogenesis (TFAM), mitophagy (BNIP3), dynamics (OPA1, MFN2, DRP1), and autophagy (p62, LC3-II/LC3-I) in liver, heart, diaphragm, and tibialis anterior (TA) from three groups of male Sprague-Dawley rats: fully grown, mature adult ad libitum-fed (A-AL, 9 months), old ad libitum-fed (O-AL, 22 months), and old calorie-restricted (O-CR, 22 months; 40% CR for 13 months). Aging increased fusion markers in the liver, diaphragm, and TA, with a similar trend in the heart, while DRP1 was unchanged in all tissues, arguing against a fission-dominant aging phenotype. Biogenesis and autophagy markers rose with age in the liver, diaphragm, and TA, and BNIP3 increased selectively in the TA. The heart showed no aging-related changes. CR prevented several age-related alterations: it attenuated the aging-induced rise in biogenesis markers in the diaphragm and TA, blunted the elevation of autophagy markers in the liver, diaphragm, and TA, and reduced fusion markers in the TA with a trend toward reduction in the diaphragm. CR also exerted tissue-specific effects: it promoted fission in the liver (trending toward an increase) while suppressing it in the TA, and elevated BNIP3 in the liver while trending toward its reduction in the TA. Overall, our results indicate that aging shifts mitochondrial dynamics toward fusion while impairing autophagy in multiple tissues, whereas the heart is largely spared. CR selectively counters these alterations and promotes fission and mitophagy in the liver, supporting a tissue-specific model in which CR attenuates aging-induced disruption of mitochondrial quality control.