Disruption of REDD1 gene ameliorates sepsis-induced decrease in mTORC1 signaling but has divergent effects on proteolytic signaling in skeletal muscle

Abstract

Steiner JL, Crowell KT, Kimball SR, Lang CH. Disruption of REDD1 gene ameliorates sepsis-induced decrease in mTORC1 signaling but has divergent effects on proteolytic signaling in skeletal muscle. Am J Physiol Endocrinol Metab 309: E981-E994, 2015. First published October 20, 2015 doi:10.1152/ajpendo.00264.2015.-Sepsis-induced skeletal muscle atrophy and weakness are due in part to decreased mTORC1-mediated protein synthesis and increased proteolysis via the autophagy-lysosomal system and ubiquitin-proteasome pathway. The REDD1 (regulated in development and DNA damage-1) protein is increased in sepsis and can negatively regulate mTORC1 activity. However, the contribution of REDD1 to the sepsis-induced change in muscle protein synthesis and degradation has not been determined. Sepsis was produced by cecal ligation and puncture in female REDD1Ϫ/Ϫ or wild-type (WT) mice, and end points were assessed 24 h later in gastrocnemius; time-matched, pair-fed controls of each genotype were included. Sepsis increased REDD1 protein 300% in WT mice, whereas REDD1 was absent in REDD1 Ϫ/Ϫ mice despite unaltered PDK1, PP2A, or TSC2 expression. Sepsis increased autophagy as indicated by decreased ULK1 Ser 757 phosphorylation and p62 abundance and increased LC3B-II/I in WT mice, whereas these changes were absent in septic REDD1 Ϫ/Ϫ mice. Conversely, REDD1 deletion did not prevent the sepsis-induced decrease in IGF-I mRNA or the concomitant increase in IL-6, TNF␣, MuRF1, and atrogin1 mRNA expression. Lastly, 5-day survival in a separate set of septic mice did not differ between WT and REDD1 Ϫ/Ϫ mice. These data highlight the central role of REDD1 in regulating both protein synthesis and autophagy in skeletal muscle during sepsis. rgulated in development and DNA damage-1; mechanistic target of rapamycin complex 1; protein synthesis; autophagy; cecal ligation and puncture; proteolysis; critical illness SKELETAL MUSCLE ATROPHY IS A DEBILITATING CONSEQUENCE of sepsis and critical illness that increases the length of hospitalization and mortality (19). Loss of muscle mass and strength during sepsis results from the prolonged imbalance between rates of protein synthesis and degradation caused by several factors, including increased proinflammatory cytokine signaling, anabolic resistance, and excess glucocorticoids (1,32,48). Protein synthesis is controlled predominantly by the mechanistic (a.k.a. mammalian) target of rapamycin complex 1 (mTORC1), which phosphorylates 70-kDa ribosomal protein S6 kinase-1 (S6K1) and eukaryotic initiation factor (eIF) 4E-binding protein-1 (4E-BP1) to increase translation initiation and peptide chain elongation within muscle (13,25). mTORC1 represents a central regulatory factor in the integration of various metabolic signals, including those induced by energy stress [AMP-activated protein kinase (AMPK), regulated in development and DNA damage-1 (REDD-1)] and growth factors (insulin/Akt). Upon activation of the insulin or insulin-like growth factor (IGF)-I receptor and the phosphoinositide 3-kinase signaling...

Is REDD1 a Metabolic Éminence Grise ?

“…Consistent with this idea, a study by Lafarge and coworkers demonstrated that the livers of mice deficient for the protease cathepsin S exhibited a lower rate of hepatocellular respiration compared with control counterparts, concomitant with elevated hepatic expression of REDD1 [77]. In addition, peritoneal sepsis has been reported to increase REDD1 protein content in skeletal muscle of mice [78], as well as to promote derangements in mitochondrial bioenergetics in this tissue [79]. Therefore, further work will be required to explore the potential link between obesity and/or diabetes, REDD1, and mitochondrial function, for example using relevant animal models of obesity and/or diabetes as well as REDD1 deficiency.…”

Restorative Mechanisms Regulating Protein Balance in Skeletal Muscle During Recovery From Sepsis

“…Activating the Akt-TSC2-mTORC1 pathway appears to represent a compensatory upregulation during the recovery phase that is capable of enhancing protein synthesis via a coordinated increase of both the initiation and elongation phase of translation. The activation of this canonical pathway is notable as it represents a complete reversal of the hypo-phosphorylation of Akt, mTOR, 4E-BP1 and S6K1, eIF4B and eEF2K detected acutely in muscle at 24 h after CLP (12, 24). …”

“…However, in the recovery phase, AMPK phosphorylation did not differ from control levels and we detected a decrease in total REDD1. Previous studies have indicated that knockdown of REDD1 protein largely prevents the acute sepsis-induced decrease in muscle protein synthesis (12). Moreover, knockdown of REDD1 also activates (phosphorylates) Akt, thereby stimulating mTORC1 (28).…”

“…Total RNA (1 μg) was reverse transcribed using superscript III reverse transcriptase (Invitrogen, Carlsbad, CA). Real-time quantitative PCR was performed using 25 ng of cDNA in StepOnePlus system using TaqMan gene expression assay (Applied Biosystems, Foster, CA) for: atrogin-1 (aka MAFbx), muscle RING-finger 1 (MuRF1), interleukin (IL)-1β, IL-6, IL-18, tumor necrosis factor (TNF)-α, and insulin-like growth factor (IGF)-I using primers as described previously (10, 12). The comparative quantitation method 2 -ΔΔCt was used to present gene expression in reference to the endogenous control, GAPDH.…”

Emerging role for regulated in development and DNA damage 1 (REDD1) in the regulation of skeletal muscle metabolism

“…Disruption of the REDD1 gene offset the sepsis-induced decrease in mTORC1 signaling [phosphorylation of p70S6K1 (Thr 389 ), 4E-BP1 (Ser 65 ), rpS6 (Ser 240/244 )] and protein synthesis (114). In addition to mediating the sepsis-related modulation of mTORC1 signaling, REDD1 also appeared to contribute to the sepsis-induced increase in autophagy.…”