A ketogenic diet impacts markers of mitochondrial mass in a tissue specific manner in aged mice

Abstract

Declines in mitochondrial mass are thought to be a hallmark of mammalian aging, and a ketogenic diet (KD) may prevent the age-related decreases in mitochondrial content. The objective of this study was to investigate the impact of a KD on markers of mitochondrial mass. Mice were fed an isocaloric control diet (CD) or KD from 12 months of age. Tissues were collected after 1 month and 14 months of intervention, and a panel of commonly used markers of mitochondrial mass (mitochondrial enzyme activities and levels, mitochondrial to nuclear DNA ratio, and cardiolipin content) were measured. Our results showed that a KD stimulated activities of marker mitochondrial enzymes including citrate synthase, Complex I, and Complex IV in hindlimb muscle in aged mice. KD also increased the activity of citrate synthase and prevented an age-related decrease in Complex IV activity in aged brain. No other markers were increased in these tissues. Furthermore, the impacts of a KD on liver and kidney were mixed with no pattern indicative of a change in mitochondrial mass. In conclusion, results of the present study suggest that a KD induces tissue-specific changes in mitochondrial enzyme activities, or structure, rather than global changes in mitochondrial mass across tissues.

Mitochondrial Dynamics and Mitophagy in Skeletal Muscle Health and Aging

“…Recently, it was reported that long-term exposure to a ketogenic diet attenuated the aging-related decline of relative muscle mass [ 173 ] and increased markers of mitochondrial content in aged skeletal muscles [ 174 ]. Interestingly, the ketone body β-hydroxybutyrate, which is elevated during nutritional ketosis, was shown to induce mitophagy in young and aged myocytes [ 175 ] and elicits favorable mitochondrial adaptations in myocytes [ 176 ].…”

A 1-Month Ketogenic Diet Increased Mitochondrial Mass in Red Gastrocnemius Muscle, but Not in the Brain or Liver of Middle-Aged Mice

“…The increase in red gastrocnemius muscle mitochondrial mass may contribute to the previous observation that aged mice on a KD perform better in muscle strength and endurance tests than CD animals [21]. However, these changes in mitochondrial mass were not reflected in the hindlimb skeletal muscle mitochondrial markers assayed at this same length of time on diet in our previous study [10]. This could indicate the markers used were not sensitive enough to pick up the differences in muscle tissues.…”

“…In our previous skeletal muscle work [ 10 ], mitochondrial markers were analyzed in homogenates of the entire hindlimb skeletal muscle, and it was not possible to determine the response of specific muscles to a KD. To directly address this issue, we harvested the red gastrocnemius muscle to measure mitochondrial content with TEM.…”

“…Instead, the TEM results likely indicate that KD-related increases in mitochondrial content in red gastrocnemius do not translate to other muscles. In our previous work, we pooled all of the muscle of the hindlimb for analysis [ 10 ], and the likely result was the greater mass of glycolytic muscles obscured the rapid change in mitochondria in the smaller oxidative muscle mass when whole hindlimb homogenates were used to study skeletal muscle. In support of this hypothesis, our recent study [ 11 ] looking specifically at the gastrocnemius muscle following two months of a KD in middle-aged mice demonstrated upregulated mitochondrial biogenesis and increased citrate synthase activity.…”

“…However, most studies used only a few markers (e.g., citrate synthase or mitochondrial DNA), which give an incomplete picture of mitochondrial changes induced by diet as each marker has its limitations, possibly leading to the discrepancies observed among studies. We have previously used a panel of common mitochondrial markers to thoroughly investigate the impact of a KD started in early middle-aged mice on mitochondrial mass in whole-tissue homogenates of hindlimb skeletal muscle, brain, and liver, and after 1 month of intervention, no concerted changes in markers of mitochondrial mass were observed [ 10 ]. However, it is not known whether mitochondrial mass in specific muscle groups or regions within a tissue may be altered with a KD.…”