Search

Skeletal muscle atrophy and weakness are major contributors to frailty and impact significantly on quality of life of older people. Muscle aging is characterized by a loss of maximum tetanic force ([P.sub.o]) generation, primarily due to muscle atrophy, to which mitochondrial dysfunction is hypothesized to contribute. We hypothesized that lifelong overexpression of the mitochondrial heat shock protein (HSP) HSP10 in muscle of mice would protect against development of these deficits. [P.sub.o] generation by extensor digitorum longus muscles of adult and old wild-type and HSP10-overexpressing mice was determined in situ. Muscles were subjected to damaging lengthening contractions, and force generation was remeasured at 3 h or 28 days to examine susceptibility to, and recovery from, damage, respectively. Muscles of old wild-type mice had a 23% deficit in [P.sub.o] generation and a 10% deficit in muscle cross-sectional area compared with muscles of adult wild-type mice. Overexpression of HSP10 prevented this age-related fall in [P.sub.o] generation and reduction in cross-sectional area observed in muscles of old wild-type mice. Additionally, overexpression of HSP10 protected against contraction-induced damage independent of age but did not improve recovery if damage occurred. Preservation of muscle force generation and CSA by HSP10 overexpression was associated with protection against the age-related accumulation of protein carbonyls. Data demonstrate that development of age-related muscle weakness may not be inevitable and show, for the first time, that lifelong overexpression of an HSP prevents the age-related loss of [P.sub.o] generation. These findings support the hypothesis that mitochondrial dysfunction is involved in the development of age-related muscle deficits. aging; heat shock protein; Cpnl0; Hspel; atrophy doi: 10.1152/ajpregu.00334.2009.

Skeletal muscle atrophy and weakness are major causes of frailty in the elderly. Functional deficits in muscles of old humans and rodents are associated with attenuated production of heat shock proteins (HSPs) after exercise, and transgenic overexpression of HSP70 reverses this functional decline. We hypothesized that training would increase HSP70 content of muscle in adult and old wild-type mice and that this would protect against the development of age-related functional deficits. A 10-wk treadmill training protocol at 15 m/min, for 15 min, 3 days/wk resulted in a significant increase in HSP70 content of muscles of adult mice. Muscles of old untrained mice demonstrated a significant increase in HSP70 protein content and a reduction in HSP70 mRNA content compared with adult untrained mice. Training for 12 mo starting at age 12-14 mo old or for 10 wk starting from age 24 mo old resulted in modification of HSP70 protein and mRNA content to levels of adult mice. Training did not change force generation of extensor digitorum longus muscles of old mice or improve recovery after damaging contractions. The twofold increase in HSP70 content in muscles of adult mice after training may have not been sufficient to provide protection in this instance. mRNA; exercise; aging; heat shock protein

Proteinuria is pathogenic to proximal tubular cells (PTC) and linked with progression to renal failure. The aim of this study was to determine the effects of human serum albumin (HSA) overload on the changes in gene and protein expression stimulated by oxidative stress in PTC and any interaction with ANG II that is pivotal in disease pathogenesis. Markers of oxidative stress, antioxidant defences, transcription factor activation, and the expression of stress-related genes were measured in human PTC (HK-2 cells) overloaded with either globulin-free fatty acid free (GF/FAF) HSA or globulin-free (GF) HSA. The effects of ANG II were also determined. HSA overload in HK-2 cells caused PTC hyperfunction, increased oxidative stress, and an upregulation of adaptive responses and stress-related genes. Some responses were common to both HSAs but others were unique to either HSA and unaffected by addition of ANG II or candesartan (a specific ANG II type 1 receptor blocker). ANG II also independently induced oxidative stress and upregulated other stress-related genes. HSA overload in HK-2 cells stimulated increased oxidative stress and upregulated changes in stress-related gene expression indicating new pathways of PTC injury that are not mediated via ANG II type 1 receptors. stress-related gene expression; HK-2 cells; cell culture; oxidative metabolism doi:10.1152/ajprenal.00265.2006

The search for a reliable, convenient indicator of Zn status was the focus of research for several decades. Plasma Zn concentration is still the most widely used clinical measurement, despite the known problems of interpretation. More recently, researchers suggested that isotopically determined kinetic parameters, such as the exchangeable Zn pool (EZP), may more accurately and reliably reflect body Zn status. The objective of this study was to examine the relationship between net body Zn loss and gain during acute changes in dietary Zn intake with biochemical and kinetic indices of Zn status. Five men participated in an 85-d Zn depletion/repletion study. Net body Zn loss and gain were determined from the difference between dietary plus intravenously administered Zn and Zn excretion. Biochemical indicators of Zn status included plasma Zn, plasma alkaline phosphatase activity, and plasma retinol binding protein concentration. Following intravenous administration of [sup.70]Zn or [sup.67]Zn, a compartmental model was used to determine EZP mass, fractional Zn absorption, endogenous zinc excretion (EZE), and plasma Zn flux. The changes in total body zinc correlated best with changes in plasma Zn ([r.sup.2] = 0.826, P < 0.001), EZE ([r.sup.2] = 0.773, P < 0.001), and plasma Zn flux ([r.sup.2] = 0.788, P < 0.001). This study confirms that plasma Zn concentration is a valid indicator of whole-body Zn status in the absence of confounding factors; however, further research is needed to determine how kinetic parameters respond to conditions where plasma Zn concentration is known to be unreliable. KEY WORDS: zinc status biochemical indices * stable isotopes * kinetic analysis * compartmental model

Both ischemia and reperfusion injury and contractile activity are associated with the generation of reactive oxygen species and free radicals by skeletal muscle. In addition, exercise has been reported to lead to the formation of a circulating free radical species that is detectable in the blood by spin trapping before analysis by electron-spin resonance (ESR) techniques. Previous analysis of the ESR signal indicated that the circulating species is either a carbon- or oxygen-centered lipid-derived free radical. The current data indicate that this species is present in the blood of anesthetized rats after 4-h ischemia and 1 h of reperfusion of a single hindlimb. During 4 h of ischemia, the species was also present in microdialysates from the tibialis anterior muscle but was unchanged in magnitude compared with control tissue. During i h of reperfusion, the signal intensity increased by a mean of 420% (P < 0.05, n = 4). Hydroxyl radical activity in the interstitial fluid also significantly increased during ischemia and further increased by a mean of 210% (P < 0.05, n = 4) during reperfusion. No changes in interstitial superoxide levels were seen, but interstitial PG[E.sub.2] content also increased during reperfusion. A significant positive correlation was found between the magnitude of the ESR signal and both the hydroxyl radical activity and [PGE.sub.2] content of microdialysis fluids. These data support the hypothesis that the circulating free radical species is formed in the interstitial fluid by hydroxyl radical interaction with a lipid that may be released from reperfused tissue with a similar pattern to prostanoids. microdialysis; electron-spin resonance; prostanoids