Catabolic Conditions Research Articles

Prevention of skeletal muscle atrophy in vitro using anti-ubiquitination oligopeptide carried by atelocollagen

Skeletal muscle atrophy occurs when the rate of protein degradation exceeds that of protein synthesis in various catabolic conditions, such as fasting, disuse, aging, and chronic diseases. Insulin-like growth factor-1 (IGF-1) signaling stimulates muscle growth and suppresses muscle protein breakdown. In atrophied muscles, ubiquitin ligase, Cbl-b, increases and stimulates the ubiquitination and degradation of IRS-1, an intermediate in IGF-1 signaling pathway, resulting in IGF-1 resistance. In this study, we evaluated the efficacy of atelocollagen (ATCOL)-transported anti-ubiquitination oligopeptide (Cblin: Cbl-b inhibitor) (consisting of tyrosine phosphorylation domain of IRS-1) in starved C2C12 myotubes. The amount of IRS-1 protein was lower in starved versus unstarved myotubes. The Cblin-ATCOL complex inhibited IRS-1 degradation in a concentration-dependent manner. Myotubes incubated with Cblin-ATCOL complex showed significant resistance to starvation-induced atrophy (p<0.01). Furthermore, the Cblin-ATCOL complex significantly inhibited any decrease in Akt phosphorylation (p<0.01) and localization of FOXO3a to the nucleus in starved myotubes. These results suggest that Cblin prevented starvation-induced C2C12 myotube atrophy by maintaining the IGF-1/Akt/FOXO signaling. Therefore, attachment of anti-ubiquitination oligopeptide, Cblin, to ATCOL enhances its delivery to myotubes and could be a potentially effective strategy in the treatment of atrophic myopathies.

FoxO transcription factors and endurance training: a role for FoxO1 and FoxO3 in exercise-induced angiogenesis.

FoxO transcription factors and endurance training: a role for FoxO1 and FoxO3 in exercise-induced angiogenesis.

S2-2 - Regulation and involvement of the ubiquitin ligases in muscle atrophy

The ability to activate compensatory mechanisms in response to environmental stress is an important factor for survival and maintenance of cellular functions. A system that is often activated both in short and prolonged stress conditions is ubiquitin proteasome system (UPS). UPS is required to clear the cell from dysfunctional and altered proteins and is reported to increase during catabolic conditions. This increase contributes to the loss of contractile proteins and, when is exacerbated, to cachexia. Here I'll present the last data about UPS regulation, the role of UPS in protein turnover in skeletal muscles and the pathogenetic implications of deregulated UPS in muscle disorders.

Effects of bed-rest on urea and creatinine: correlation with changes in fat-free mass.

BackgroundBed-rest experiments are designed for investigation on catabolic effects of hypokinetic conditions and/or for microgravity simulation in on-ground aerospace research. Bed-rest effects include a reduction in fat-free mass and muscle mass. Urea and creatinine are catabolites of endogenous protein and of muscular energetic metabolism which are excreted mainly by the kidney. The study investigated on urea, creatinine, and kidney function during bed-rest.MethodsTwenty healthy young men underwent a 7-day adaptation period (day-6 to day-0) and a 35-day bed-rest experiment (day1 to day35) during normocaloric diet. Urine were collected from day-3 to day0 (baseline) and from day1 to day35. Blood samples and anthropometrical data were collected at day0 (baseline) and bed-rest days 7, 14, 21, 28, and 35.ResultsBed-rest reduced plasma volume, weight, fat-free mass, and muscle mass (P<0.001). During bed-rest there was a transient increase in plasma and urinary urea, a decrease in plasma creatinine, and no change in urinary creatinine. The overall integral of changes from day0 to day35 was on average +101.7 mg/dL for plasma urea (95%CI = +43.4/+159.9), +82.2 g/24 h for urinary urea (95%CI = +55.8/+108.7), −2.5 mg/dL for plasma creatinine (95%CI = −3.1/−1.9). Bed-rest reduced plasma cistatyn C also, which was used as mass-independent marker of glomerular filtration rate (−13.1%, P<0.05). Correlations with final reduction in fat-free mass and muscle mass were significant for the overall integral of changes in urinary urea from day0 to day35 (R = 0.706, P<0.001) and for early changes in urinary urea and plasma urea from day0 to day7 (R = 0.566, P = 0.009 and R = 0.715, P<0.001, respectively).ConclusionsStudy results shows that urea is a marker of catabolic conditions secondary to hypokinetic conditions.

Arginine protects muscle cells from wasting in vitro in an mTORC1-dependent and NO-independent manner.

Amino acids are potent regulators of muscle protein synthesis and breakdown and have received considerable attention for the treatment of muscle wasting conditions. Arginine is critically involved in numerous physiological functions including providing substrate for the production of creatine, urea and nitric oxide (NO) and in the synthesis of new proteins. However, little is known about the direct effects of arginine on skeletal muscle protein synthesis during catabolic conditions. The aims of this study were to determine whether exogenous arginine could protect skeletal muscle cells from wasting directly and whether this effect was dependent on production of NO and/or activation of the rapamycin-sensitive mechanistic target of rapamycin complex 1 (mTORC1) signalling pathway. To explore these aims, we deprived mature C2C12 myotubes from nutrients and growth factors by incubating them in HEPES buffered saline with arginine or equimolar concentrations of alanine (control). Our results show that arginine: increased the ratio of phosphorylated to total mTOR (146 %), S6 (40 %) and 4EBP1 (69 %); increased protein synthesis (69 %) during the first hour of treatment; and increased myotube diameter by ~15 %. Experiments using the NO synthase inhibitor L-NG-Nitroarginine Methyl Ester showed a NO-independent protection from muscle wasting. On the other hand, the mTORC1 inhibitor rapamycin prevented increases in phosphorylated S6, protein synthesis and myotube diameter. The activation of mTORC1 and protein synthesis by arginine was not associated with changes in the phosphorylation status of Akt, but rather increased the expression of the amino acid-sensitive type III PI3-kinase Vps34 signalling protein. These data support a direct role for arginine in the regulation of mTORC1 in skeletal muscle.

Involvement of MicroRNAs in the Regulation of Muscle Wasting during Catabolic Conditions

Loss of muscle proteins and the consequent weakness has important clinical consequences in diseases such as cancer, diabetes, chronic heart failure, and in aging. In fact, excessive proteolysis causes cachexia, accelerates disease progression, and worsens life expectancy. Muscle atrophy involves a common pattern of transcriptional changes in a small subset of genes named atrophy-related genes or atrogenes. Whether microRNAs play a role in the atrophy program and muscle loss is debated. To understand the involvement of miRNAs in atrophy we performed miRNA expression profiling of mouse muscles under wasting conditions such as fasting, denervation, diabetes, and cancer cachexia. We found that the miRNA signature is peculiar of each catabolic condition. We then focused on denervation and we revealed that changes in transcripts and microRNAs expression did not occur simultaneously but were shifted. Indeed, whereas transcriptional control of the atrophy-related genes peaks at 3 days, changes of miRNA expression maximized at 7 days after denervation. Among the different miRNAs, microRNA-206 and -21 were the most induced in denervated muscles. We characterized their pattern of expression and defined their role in muscle homeostasis. Indeed, in vivo gain and loss of function experiments revealed that miRNA-206 and miRNA-21 were sufficient and required for atrophy program. In silico and in vivo approaches identified transcription factor YY1 and the translational initiator factor eIF4E3 as downstream targets of these miRNAs. Thus miRNAs are important for fine-tuning the atrophy program and their modulation can be a novel potential therapeutic approach to counteract muscle loss and weakness in catabolic conditions.

FOXO1 activates glutamine synthetase gene in mouse skeletal muscles through a region downstream of 3'-UTR: possible contribution to ammonia detoxification.

Skeletal muscle is a reservoir of energy in the form of protein, which is degraded under catabolic conditions, resulting in the formation of amino acids and ammonia as a byproduct. The expression of FOXO1, a forkhead-type transcription factor, increases during starvation and exercise. In agreement, transgenic FOXO1-Tg mice that overexpress FOXO1 in skeletal muscle exhibit muscle atrophy. The aim of this study was to examine the role of FOXO1 in amino acid metabolism. The mRNA and protein expressions of glutamine synthetase (GS) were increased in skeletal muscle of FOXO1-Tg mice. Fasting induced FOXO1 and GS expression in wild-type mice but hardly increased GS expression in muscle-specific FOXO1 knockout (FOXO1-KO) mice. Activation of FOXO1 also increased GS mRNA and protein expression in C2C12 myoblasts. Using a transient transfection reporter assay, we observed that FOXO1 activated the GS reporter construct. Mutation of a putative FOXO1-binding consensus sequence in the downstream genomic region of GS decreased basal and FOXO1-dependent reporter activity significantly. A chromatin immunoprecipitation assay showed that FOXO1 was recruited to the 3' region of GS in C2C12 myoblasts. These results suggest that FOXO1 directly upregulates GS expression. GS is considered to mediate ammonia clearance in skeletal muscle. In agreement, an intravenous ammonia challenge increased blood ammonia concentrations to a twofold higher level in FOXO1-KO than in wild-type mice, demonstrating that the capacity for ammonia disposal correlated inversely with the expression of GS in muscle. These data indicate that FOXO1 plays a role in amino acid metabolism during protein degradation in skeletal muscle.

Exacerbated oxidative stress in the fasting liver according to fuel partitioning.

Complete starvation may prove lethal due to excessive loss of body proteins. However, it is still not completely understood whether responses to food deprivation are time-dependently induced or triggered in relation with the successive phases of protein sparing and wasting that characterize prolonged fasting. As the liver has a wide range of vital functions, we examined the hepatic regulatory mechanisms elicited during prolonged fasting. We showed that fasting-induced transcriptome/proteome changes occur in close relation with fuel partitioning, independently of ATP levels. Omics data suggesting a worsening of oxidative stress during the proteolytic stage of fasting were further validated using biochemical assays. Low levels of antioxidant factors were indeed paralleled by their decreased activity that could be impaired by low NADPH levels. Oxidative damage to lipids and proteins was accordingly increased only during late fasting. At this stage, the gene/protein expression of several chaperones was also repressed. Together with the impairment of metabolic achievements, a vicious cycle involving protein misfolding and oxidative stress could jeopardize liver function when the proteolytic stage of fasting is reached. Thus, monitoring of liver impairments should help to better manage or treat catabolic and/or oxidative stress conditions, such as ageing and degeneration.

Glutamine and intestinal barrier function.

The intestinal barrier integrity is essential for the absorption of nutrients and health in humans and animals. Dysfunction of the mucosal barrier is associated with increased gut permeability and development of multiple gastrointestinal diseases. Recent studies highlighted a critical role for glutamine, which had been traditionally considered as a nutritionally non-essential amino acid, in activating the mammalian target of rapamycin cell signaling in enterocytes. In addition, glutamine has been reported to enhance intestinal and whole-body growth, to promote enterocyte proliferation and survival, and to regulate intestinal barrier function in injury, infection, weaning stress, and other catabolic conditions. Mechanistically, these effects were mediated by maintaining the intracellular redox status and regulating expression of genes associated with various signaling pathways. Furthermore, glutamine stimulates growth of the small intestinal mucosa in young animals and also enhances ion transport by the gut in neonates and adults. Growing evidence supports the notion that glutamine is a nutritionally essential amino acid for neonates and a conditionally essential amino acid for adults. Thus, as a functional amino acid with multiple key physiological roles, glutamine holds great promise in protecting the gut from atrophy and injury under various stress conditions in mammals and other animals.

Haptoglobin is required to prevent oxidative stress and muscle atrophy.

BackgroundOxidative stress (OS) plays a major role on tissue function. Several catabolic or stress conditions exacerbate OS, inducing organ deterioration. Haptoglobin (Hp) is a circulating acute phase protein, produced by liver and adipose tissue, and has an important anti-oxidant function. Hp is induced in pro-oxidative conditions such as systemic inflammation or obesity. The role of systemic factors that modulate oxidative stress inside muscle cells is still poorly investigated.ResultsWe used Hp knockout mice (Hp-/-) to determine the role of this protein and therefore, of systemic OS in maintenance of muscle mass and function. Absence of Hp caused muscle atrophy and weakness due to activation of an atrophy program. When animals were stressed by acute exercise or by high fat diet (HFD), OS, muscle atrophy and force drop were exacerbated in Hp-/-. Depending from the stress condition, autophagy-lysosome and ubiquitin-proteasome systems were differently induced.ConclusionsHp is required to prevent OS and the activation of pathways leading to muscle atrophy and weakness in normal condition and upon metabolic challenges.

Nutritional status and growth hormone regulate insulin-like growth factor binding protein (igfbp) transcripts in Mozambique tilapia

Growth in teleosts is controlled in large part by the activities of the growth hormone (Gh)/insulin-like growth factor (Igf) system. In this study, we initially identified igf-binding protein (bp)1b, -2b, -4, -5a and -6b transcripts in a tilapia EST library. In Mozambique tilapia (Oreochromis mossambicus), tissue expression profiling of igfbps revealed that igfbp1b and -2b had the highest levels of expression in liver while igfbp4, -5a and -6b were expressed at comparable levels in most other tissues. We compared changes in hepatic igfbp1b, -2b and -5a expression during catabolic conditions (28days of fasting) along with key components of the Gh/Igf system, including plasma Gh and Igf1 and hepatic gh receptor (ghr2), igf1 and igf2 expression. In parallel with elevated plasma Gh and decreased Igf1 levels, we found that hepatic igfbp1b increased substantially in fasted animals. We then tested whether systemic Gh could direct the expression of igfbps in liver. A single intraperitoneal injection of ovine Gh into hypophysectomized tilapia specifically stimulated liver igfbp2b expression along with plasma Igf1 and hepatic ghr2 levels. Our collective data suggest that hepatic endocrine signaling during fasting may involve post-translational regulation of plasma Igf1 via a shift towards the expression of igfbp1b. Thus, Igfbp1b may operate as a molecular switch to restrict Igf1 signaling in tilapia; furthermore, we provide new details regarding isoform-specific regulation of igfbp expression by Gh.

Editorial introductions

Editorial introductions

Correlation of synovial cytokine expression with quality of cells used for autologous chondrocyte implantation in human knees

The cell quality plays a decisive role in autologous chondrocyte implantation (ACI). Aim of the study was the analysis of in vivo interactions between synovial concentrations of cytokines and cell quality used for ACI. Knee lavage fluids of patients undergoing an ACI were examined for total protein content (TPC) and by ELISA for levels of basic fibroblast growth factor (bFGF), insulin-like growth factor 1, bone morphogenetic proteins 2 and 7 (BMP-2 and BMP-7). Cell quality following amplification for ACI was determined by surface expression of CD44, aggrecan, collagen type II and evaluation of cell characteristics. Data of 17 patients were supplemented by epidemiological parameters and clinical scores (IKDC, Lysholm, pain strength, subjective knee function). CD44 expression was positively associated with TPC and bFGF, and negatively linked to BMP-2 levels (p < 0.01). In contrast, expression of collagen type II did not show any statistically significant correlations with synovial protein concentrations. TPC was positively associated with intraarticular bFGF levels and pain strength (p < 0.01), both indicators for osteoarthritis (OA). Correlating with the negative relation of TPC and BMP-2, subjective knee function after 1 year was positively linked to intraarticular BMP-2 concentrations (p < 0.001). Similarly, expression of collagen type II indicated a favorable clinical result reaching statistical significance in case of pain strength (p < 0.01). Initially increased bFGF levels and CD44 expression indicated a worse clinical outcome after 1 year (IKDC, Lysholm Scores, pain strength). Surface expression of CD44 on chondrocytes used for ACI was negatively associated with synovial BMP-2 and positively to TPC and bFGF indicating catabolic synovial conditions. These correlations were also reflected by clinical outcome parameters.

Attenuation of muscle wasting in murine C2C12 myotubes by epigallocatechin‐3‐gallate

BackgroundLoss of muscle protein is a common feature of wasting diseases where currently treatment is limited. This study investigates the potential of epigallocatechin-3-gallate (EGCg), the most abundant catechin in green tea, to reverse the increased protein degradation and rescue the decreased protein synthesis which leads to muscle atrophy.MethodsStudies were conducted in vitro using murine C2C12 myotubes. Increased protein degradation and reduced rates of protein synthesis were induced by serum starvation and tumour necrosis factor-α (TNF-α).ResultsEGCg effectively attenuated the depression of protein synthesis and increase in protein degradation in murine myotubes at concentrations as low as 10 μM. Serum starvation increased expression of the proteasome 20S and 19S subunits, as well as the proteasome ‘chymotrypsin-like’ enzyme activity, and these were all attenuated down to basal values in the presence of EGCg. Serum starvation did not increase expression of the ubiquitin ligases MuRF1 and MAFbx, but EGCg reduced their expression below basal levels, possibly due to an increased expression of phospho Akt (pAkt) and phospho forkhead box O3a (pFoxO3a). Attenuation of protein degradation by EGCg was increased in the presence of ZnSO4, suggesting an EGCg-Zn2+ complex may be the active species.ConclusionThe ability of EGCg to attenuate depressed protein synthesis and increase protein degradation in the myotubule model system suggests that it may be effective in preserving skeletal muscle mass in catabolic conditions.

HDAC1 activates FoxO and is both sufficient and required for skeletal muscle atrophy

The Forkhead box O (FoxO) transcription factors are activated, and necessary for the muscle atrophy, in several pathophysiological conditions, including muscle disuse and cancer cachexia. However, the mechanisms that lead to FoxO activation are not well defined. Recent data from our laboratory and others indicate that the activity of FoxO is repressed under basal conditions via reversible lysine acetylation, which becomes compromised during catabolic conditions. Therefore, we aimed to determine how histone deacetylase (HDAC) proteins contribute to activation of FoxO and induction of the muscle atrophy program. Through the use of various pharmacological inhibitors to block HDAC activity, we demonstrate that class I HDACs are key regulators of FoxO and the muscle-atrophy program during both nutrient deprivation and skeletal muscle disuse. Furthermore, we demonstrate, through the use of wild-type and dominant-negative HDAC1 expression plasmids, that HDAC1 is sufficient to activate FoxO and induce muscle fiber atrophy in vivo and is necessary for the atrophy of muscle fibers that is associated with muscle disuse. The ability of HDAC1 to cause muscle atrophy required its deacetylase activity and was linked to the induction of several atrophy genes by HDAC1, including atrogin-1, which required deacetylation of FoxO3a. Moreover, pharmacological inhibition of class I HDACs during muscle disuse, using MS-275, significantly attenuated both disuse muscle fiber atrophy and contractile dysfunction. Together, these data solidify the importance of class I HDACs in the muscle atrophy program and indicate that class I HDAC inhibitors are feasible countermeasures to impede muscle atrophy and weakness.

Progressive Resistance Exercise Training Attenuated Renal Damages, but did not improve Muscle Force in STZ-Induced Diabetic Rats

A type of exercise (Resistance Exercise Training – RET) that is markedly applied to increase muscle mass has been prescribed to prevent muscle atrophy from catabolic conditions such as, diabetes and chronic kidney disease. However, how this type of exercise modulates renal system remains unclear. It prompted us to apply progressive RET to STZ-induced diabetes rats in order to investigate renal environment. Progressive RET was applied to Wistar rats under following exercise program: 6 to 12 climbs/day, 5 days/week, 8 weeks, at 50 to 80% of maximal loading test. After streptozotocin injection, animals were divided into four groups: two control groups (non-exercised and exercised) and two diabetic groups (non-exercised and exercised) with 4 to 6 rats/group. Kidney weight (KW), muscle weight, proteinuria and protein level (assessed by Western blot and multiplex technology) were determined. It was found that RET did not protect exercised diabetic animals from loss of muscle mass. RET did not influence the performance in maximal loading test in diabetic groups (p>0.05); additionally exercised diabetic animals did not recover body weight (p>0.05). KW was preserved in exercised diabetic animals meanwhile proteinuria was lowering as well (15.83 ± 2.6 mg/24h) when compared to diabetic group (37.66 ± 3.2 mg/24h, p<0.05). We assessed upstream and downstream of mTOR and found significant decreases in PI3K, p-Akt and p-4EBP1 in kidneys of exercised diabetic animals (p<0.05). Moreover, we observed that kidney protein level of TGFβ-1 was markedly decreased in exercised diabetic animals. Under progressive RET program, kidneys may be functionally protected and mTOR-signaling pathway plays important role on renal environment. However, skeletal muscle showed no improvement under this program, suggesting different mTOR modulation among renal and muscle functions

Stat3 Activation Links a C/EBPδ to Myostatin Pathway to Stimulate Loss of Muscle Mass

Catabolic conditions like chronic kidney disease (CKD) cause loss of muscle mass by unclear mechanisms. In muscle biopsies from CKD patients, we found activated Stat3 (p-Stat3) and hypothesized that p-Stat3 initiates muscle wasting. We created mice with muscle-specific knockout (KO) that prevents activation of Stat3. In these mice, losses of body and muscle weights were suppressed in models with CKD or acute diabetes. A small-molecule that inhibits Stat3 activation produced similar responses, suggesting a potential for translation strategies. Using CCAAT/enhancer-binding protein δ (C/EBPδ) KO mice and C2C12 myotubes with knockdown of C/EBPδ or myostatin, we determined that p-Stat3 initiates muscle wasting via C/EBPδ, stimulating myostatin, a negative muscle growth regulator. C/EBPδ KO also improved survival of CKD mice. We verified that p-Stat3, C/EBPδ, and myostatin were increased in muscles of CKD patients. The pathway from p-Stat3 to C/EBPδ to myostatin and muscle wasting could identify therapeutic targets that prevent muscle wasting.

Signal regulatory protein-α interacts with the insulin receptor contributing to muscle wasting in chronic kidney disease

Insulin resistance from chronic kidney disease (CKD) stimulates muscle protein wasting but mechanisms causing this resistance are controversial. To help resolve this, we used microarray analyses to identify initiators of insulin resistance in the muscles of mice with CKD, glucose intolerance and insulin resistance. CKD raised mRNAs of inflammatory cytokines in muscles and there was a 5.2-fold increase in signal regulatory protein-α (SIRP-α), a transmembrane glycoprotein principally present in muscle membranes. By immunoprecipitation we found it interacts with the insulin receptor and insulin receptor substrate-1 (IRS-1). Treatment of myotubes with a mixture of inflammatory cytokines showed that SIRP-α expression was increased by a NF-κB-dependent pathway. Blockade of NF-κB using a small molecule chemical inhibitor or a dominant-negative IKKβ reduced cytokine-induced SIRP-α expression. The overexpression of SIRP-α in myotubes impaired insulin signaling and raised proteolysis while SIRP-α knockdown with siRNAs in skeletal muscle cells increased tyrosine phosphorylation of the insulin receptor and IRS-1 despite inclusion of cytokines. This led to increased p-Akt and suppression of protein degradation. Thus, SIRP-α is part of a novel mechanism for inflammation-mediated insulin resistance in muscle. In catabolic conditions with impaired insulin signaling, targeting SIRP-α may improve insulin sensitivity and prevent muscle atrophy.

HMB attenuates muscle loss during sustained energy deficit induced by calorie restriction and endurance exercise

ObjectiveTo investigate the efficacy and underlying mechanisms of β-hydroxy-β-methylbutyrate (HMB) on body composition, muscle mass and physical performance under catabolic versus normal training conditions. Materials/MethodsMice were divided into four groups (n=10/group): 1) ALT=ad libitum+trained (1h/d for 3d/wk); 2) ALTH=ALT+HMB (0.5g/kg BW/d); 3) C=calorie restricted (−30%)+trained (6h/d, 6d/wk); and 4) CH=C+HMB. Repeated in vivo assessments included body composition, grip strength and sensorimotor coordination before and after the experimental protocol, while in vitro analyses included muscle wet weights, expression of selected genes and proteins regulating muscle mass, and myofiber cross-sectional area. ANOVAs were used with significance set at p<0.05. ResultsALTH had greater lean mass than ALT and sensorimotor function increased in ALTH, but decreased in ALT under normal training conditions. Grip strength decreased only in C, but was maintained in CH. Gastrocnemius mass and myofiber CSA were greater in CH than C following catabolic conditions. Gastrocnemius atrogin-1 mRNA expression was elevated in C but not in CH compared to all other groups whereas atrogin-1 protein levels showed no significant changes. ConclusionHMB improves body composition and sensorimotor function during normal training and attenuates muscle mass and strength loss during catabolic conditions.

Evidence-Based Recommendations for Optimal Dietary Protein Intake in Older People: A Position Paper From the PROT-AGE Study Group

New evidence shows that older adults need more dietary protein than do younger adults to support good health, promote recovery from illness, and maintain functionality. Older people need to make up for age-related changes in protein metabolism, such as high splanchnic extraction and declining anabolic responses to ingested protein. They also need more protein to offset inflammatory and catabolic conditions associated with chronic and acute diseases that occur commonly with aging. With the goal of developing updated, evidence-based recommendations for optimal protein intake by older people, the European Union Geriatric Medicine Society (EUGMS), in cooperation with other scientific organizations, appointed an international study group to review dietary protein needs with aging (PROT-AGE Study Group). To help older people (>65 years) maintain and regain lean body mass and function, the PROT-AGE study group recommends average daily intake at least in the range of 1.0 to 1.2 g protein per kilogram of body weight per day. Both endurance- and resistance-type exercises are recommended at individualized levels that are safe and tolerated, and higher protein intake (ie, ≥ 1.2 g/kg body weight/d) is advised for those who are exercising and otherwise active. Most older adults who have acute or chronic diseases need even more dietary protein (ie, 1.2-1.5 g/kg body weight/d). Older people with severe kidney disease (ie, estimated GFR <30 mL/min/1.73 m(2)), but who are not on dialysis, are an exception to this rule; these individuals may need to limit protein intake. Protein quality, timing of ingestion, and intake of other nutritional supplements may be relevant, but evidence is not yet sufficient to support specific recommendations. Older people are vulnerable to losses in physical function capacity, and such losses predict loss of independence, falls, and even mortality. Thus, future studies aimed at pinpointing optimal protein intake in specific populations of older people need to include measures of physical function.