4E‐BP1 and 4E‐BP2 double knockout mice are protected from aging‐associated sarcopenia

Abstract

Background Sarcopenia is the loss of muscle mass/function that occurs during the aging process. The links between mechanistic target of rapamycin (mTOR) activity and muscle development are largely documented, but the role of its downstream targets in the development of sarcopenia is poorly understood. Eukaryotic initiation factor 4E‐binding proteins (4E‐BPs) are targets of mTOR that repress mRNA translation initiation and are involved in the control of several physiological processes. However, their role in skeletal muscle is still poorly understood. The goal of this study was to assess how loss of 4E‐BP1 and 4E‐BP2 expression impacts skeletal muscle function and homeostasis in aged mice and to characterize the associated metabolic changes by metabolomic and lipidomic profiling. Methods Twenty‐four‐month‐old wild‐type and whole body 4E‐BP1/4E‐BP2 double knockout (DKO) mice were used to measure muscle mass and function. Protein homeostasis was measured ex vivo in extensor digitorum longus by incorporation of l ‐[U‐ 14 C]phenylalanine, and metabolomic and lipidomic profiling of skeletal muscle was performed by Metabolon, Inc. Results The 4E‐BP1/2 DKO mice exhibited an increase in muscle mass that was associated with increased grip strength ( P < 0.05). Protein synthesis was higher under both basal (+102%, P < 0.05) and stimulated conditions (+65%, P < 0.05) in DKO skeletal muscle. Metabolomic and complex lipid analysis of skeletal muscle revealed robust differences pertaining to amino acid homeostasis, carbohydrate abundance, and certain aspects of lipid metabolism. In particular, levels of most free amino acids were lower within the 4E‐BP1/2 DKO muscle. Interestingly, although glucose levels were unchanged, differences were observed in the isobaric compound maltitol/lactitol (33‐fold increase, P < 0.01) and in several additional carbohydrate compounds. 4E‐BP1/2 depletion also resulted in accumulation of medium‐chain acylcarnitines and a 20% lower C2/C0 acylcarnitine ratio ( P < 0.01) indicative of reduced β‐oxidation. Conclusions Taken together, these findings demonstrate that deletion of 4E‐BPs is associated with perturbed energy metabolism in skeletal muscle and could have beneficial effects on skeletal muscle mass and function in aging mice. They also identify 4E‐BPs as potential targets for the treatment of sarcopenia.

mTOR and S6K1 drive polycystic kidney by the control of Afadin-dependent oriented cell division

“…Interfering with other major outputs of mTORC1 activity, such as autophagy and cap-dependent translation, does not seem to affect cyst formation. Autophagy mutants and 4E-BP1/4E-BP2-deficient mice do not recapitulate a polycystic kidney phenotype 52,53 . We can speculate that the S6K1dependent phosphoproteome orchestrates a pleiotropic response required for the intense tissue remodeling in polycystic kidneys.…”

Betaine Delayed Muscle Loss by Attenuating Samtor Complex Inhibition for mTORC1 Signaling Via Increasing SAM Level

“…[ 37 ] Previous studies also reported that mice knocking out 4EBP1 showed a reduction in adipose tissue but mice knocking out 4EBP1 and 4EBP2 reversed this phenomenon. [ 38,39 ] These results indicated that the tissue‐specific effect mediated by different 4E‐BP family members in the regulation of metabolic homeostasis might be masked in whole‐body knockout mice. Effect of 4EBP varies from mice at different age.…”

Experimental Models of Sarcopenia: Bridging Molecular Mechanism and Therapeutic Strategy

“…For example, the Eif4ebp1 −/− and Eif4ebp2 −/− double knockdown (4EBP1/2 DKO) mice have been used to study the regulation of skeletal muscle protein synthesis. The depletion of 4E-BPs is associated with perturbed energy metabolism in skeletal muscles, and it has also been suggested that 4E-BP can be a target of sarcopenia intervention [ 158 ]. The use of growth hormone receptor knockout (GHR −/− ) and bovine GH mice provided evidence that the insulin-like growth factor 1 (IGF-1) signaling pathway predominantly regulates myostatin, which is a negative regulator of myogenesis [ 159 ].…”