Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 11 (1), 150-61

A Comprehensive Assessment of Mitochondrial Protein Synthesis and Cellular Proliferation With Age and Caloric Restriction

Affiliations

A Comprehensive Assessment of Mitochondrial Protein Synthesis and Cellular Proliferation With Age and Caloric Restriction

Benjamin F Miller et al. Aging Cell.

Abstract

It is proposed that caloric restriction (CR) increases mitochondrial biogenesis. However, it is not clear why CR increases an energetically costly biosynthetic process. We hypothesized that 40% CR would decrease mitochondrial protein synthesis and would be regulated by translational rather than transcriptional mechanisms. We assessed cumulative mitochondrial protein synthesis over 6 weeks and its transcriptional and translational regulation in the liver, heart, and skeletal muscle of young (6 month), middle (12 month), and old (24 month) male B6D2F1 mice that were lifelong CR or ad lib (AL) controls. Mitochondrial protein synthesis was not different between AL and CR (fractional synthesis over 6 weeks (range): liver, 91-100%; heart, 74-85%; skeletal muscle, 53-72%) despite a decreased cellular proliferation in liver and heart with CR. With CR, there was an increase in AMP-activated protein kinase phosphorylation/total (P:T) in heart and liver, and an increase in peroxisome proliferator-activated receptor gamma coactivator 1-α mRNA in all tissues, but not protein. Ribosomal protein S6 was decreased with CR. In conclusion, CR maintained mitochondrial protein synthesis while decreasing cellular proliferation during a time of energetic stress, which is consistent with the concept that CR increases somatic maintenance. Alternative mechanisms to global translation initiation may be responsible for selective translation of mitochondrial proteins.

Figures

Figure 1
Figure 1
Mitochondrial protein synthesis over a 6-week period in young, middle, and old AL or CR mice. Liver mitochondrial protein was fully turned over in the 6-week period (A). Heart mitochondrial protein synthesis was less than liver and there was no difference because of age or CR (B). Skeletal muscle mitochondrial protein synthesis was less than heart and had a significant effect of age (p ≤ 0.05), but not because of CR (C). Figure insets for heart and skeletal muscle are in units of %/hr. It was not possible to calculate %/hr for liver since proteins were fully turned over. n = 6–8 per group.
Figure 2
Figure 2
Cellular proliferation as measured by DNA synthesis over a 6-week period in young, middle, and old AL or CR mice. In liver (A) and heart (B) there were significant decreases in cellular proliferation in CR mice. In heart, there was a trend (p = 0.07) for increased cellular proliferation with age. In skeletal muscle there were no differences in cellular proliferation (C) although it is worth noting that there was measureable DNA synthesis in skeletal muscle. n = 6–8 per group.
Figure 3
Figure 3
PGC-1α was assessed by qPCR and western blot for potential transcriptional regulation of mitochondrial protein synthesis in liver (A), heart (B) and skeletal muscle (C). CR increased skeletal muscle PGC-1α at old age. There were no other differences in any tissue or at any age. *Significant difference between AL and CR, p ≤ 0.05, #Significant effect of age, p ≤ 0.05. n = 4–5 per group.
Figure 4
Figure 4
AMPK was assessed by qPCR and western blot for potential transcriptional regulation of mitochondrial protein synthesis in liver (A), heart (B) and skeletal muscle (C). P:T of AMPK was significantly greater in CR versus AL in liver and heart and in liver there was also a significant increase with age. In skeletal muscle there were no changes noted for AMPK. *Significant difference between AL and CR, p ≤ 0.05. n = 4–5 per group.
Figure 5
Figure 5
Assessment of global translation initiation by changes in 4e-BP-1 activation in liver (A), heart (B), and skeletal muscle (C). There was a significant increased phosphorylation in liver with CR, which indicates decreased translation initiation. Skeletal muscle appears to have variable results since total 4e-BP decreases with CR and age, but not phosphorylation. In heart phopshorylation decreased with age. *Significant difference between AL and CR, p ≤ 0.05. n = 5 per group.
Figure 6
Figure 6
Assessment of global translation initiation by changes in RpS6 activation in liver (A), heart (B), and skeletal muscle (C). In general, there is a decrease in global translation initiation in all three tissues. These changes were reflected in total, phosphorylation or the ratio. *Significant difference between AL and CR, p ≤ 0.05, #Significant effect of age, p ≤ 0.05. n = 5 per group.

Similar articles

See all similar articles

Cited by 49 PubMed Central articles

See all "Cited by" articles

Publication types

MeSH terms

Feedback