GADD45A is a mediator of mitochondrial loss, atrophy, and weakness in skeletal muscle
George R. Marcotte, … , Scott M. Ebert, Christopher M. Adams
George R. Marcotte, … , Scott M. Ebert, Christopher M. Adams
Published October 10, 2023
Citation Information: JCI Insight. 2023;8(22):e171772. https://doi.org/10.1172/jci.insight.171772.
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Research Article Metabolism Muscle biology

GADD45A is a mediator of mitochondrial loss, atrophy, and weakness in skeletal muscle

Abstract

Aging and many illnesses and injuries impair skeletal muscle mass and function, but the molecular mechanisms are not well understood. To better understand the mechanisms, we generated and studied transgenic mice with skeletal muscle–specific expression of growth arrest and DNA damage inducible α (GADD45A), a signaling protein whose expression in skeletal muscle rises during aging and a wide range of illnesses and injuries. We found that GADD45A induced several cellular changes that are characteristic of skeletal muscle atrophy, including a reduction in skeletal muscle mitochondria and oxidative capacity, selective atrophy of glycolytic muscle fibers, and paradoxical expression of oxidative myosin heavy chains despite mitochondrial loss. These cellular changes were at least partly mediated by MAP kinase kinase kinase 4, a protein kinase that is directly activated by GADD45A. By inducing these changes, GADD45A decreased the mass of muscles that are enriched in glycolytic fibers, and it impaired strength, specific force, and endurance exercise capacity. Furthermore, as predicted by data from mouse models, we found that GADD45A expression in skeletal muscle was associated with muscle weakness in humans. Collectively, these findings identify GADD45A as a mediator of mitochondrial loss, atrophy, and weakness in mouse skeletal muscle and a potential target for muscle weakness in humans.

Authors

George R. Marcotte, Matthew J. Miller, Hawley E. Kunz, Zachary C. Ryan, Matthew D. Strub, Patrick M. Vanderboom, Carrie J. Heppelmann, Sarah Chau, Zachary D. Von Ruff, Sean P. Kilroe, Andrew T. McKeen, Jason M. Dierdorff, Jennifer I. Stern, Karl A. Nath, Chad E. Grueter, Vitor A. Lira, Andrew R. Judge, Blake B. Rasmussen, K. Sreekumaran Nair, Ian R. Lanza, Scott M. Ebert, Christopher M. Adams

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Figure 7

GADD45A reduces skeletal muscle oxidative capacity in an MEKK4-dependent manner.

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GADD45A reduces skeletal muscle oxidative capacity in an MEKK4-dependent...
TA muscles of 8-week-old male C57BL/6 mice were transfected with plasmid DNA. (A–E) One TA per mouse was transfected with 2.5 mg empty plasmid (control), and the contralateral TA in each mouse was transfected with 2.5 mg GADD45A plasmid. (A–C) Seven days posttransfection, mitochondria from bilateral TAs were isolated and used for quantification of mitochondrial protein (A), mitochondrial respiration normalized to the amount of skeletal muscle (B), and mitochondrial respiration normalized to the amount of mitochondrial protein (C). (D and E) Seven days posttransfection, bilateral TAs were sectioned and subjected to immunohistochemical analysis of SDH activity. (D) Quantification of total SDH activity in entire muscle cross sections. (E) Representative images. (F and G) One TA per mouse was transfected with 2.5 mg GADD45A plasmid + 10 mg nontargeting control RNAi plasmid (control), and the contralateral TA in each mouse was transfected with 2.5 mg GADD45A plasmid + 10 mg RNAi plasmid targeting MEKK4. Seven days later, bilateral TAs were sectioned and subjected to immunohistochemical analysis of SDH activity. (F) Quantification of total SDH activity in entire muscle cross sections. (G) Representative images. (H and I) One TA per mouse was transfected with 7.5 mg empty plasmid (control), and the contralateral TA in each mouse was transfected with 7.5 mg plasmid encoding MEKK4ΔN. (H and I) Fourteen days posttransfection, bilateral TAs were sectioned and subjected to immunohistochemical analysis of SDH activity. (H) Quantification of total SDH activity in entire muscle cross sections. (I) Representative images. In A–D, F, and H, each data point represents the value from 1 muscle and bars indicate mean values. P values were determined with paired 2-tailed t tests. In A–C, **P < 0.01 and *P < 0.05.