Effects of T3 treatment on HSP72 and calcineurin content of functionally overloaded rat plantaris muscle

Effect of resistance exercise training on expression of Hsp70 and inflammatory cytokines in skeletal muscle and adipose tissue of STZ-induced diabetic rats

Impairment of adipose tissue and skeletal muscles accrued following type 1 diabetes is associated with protein misfolding and loss of adipose mass and skeletal muscle atrophy. Resistance training can maintain muscle mass by changing both inflammatory cytokines and stress factors in adipose tissue and skeletal muscle. The purpose of this study was to determine the effects of a 5-week ladder climbing resistance training program on the expression of Hsp70 and inflammatory cytokines in adipose tissue and fast-twitch flexor hallucis longus (FHL) and slow-twitch soleus muscles in healthy and streptozotocin-induced diabetic rats. Induction of diabetes reduced body mass, while resistance training preserved FHL muscle weight in diabetic rats without any changes in body mass. Diabetes increased Hsp70 protein content in skeletal muscles, adipose tissue, and serum. Hsp70 protein levels were decreased in normal and diabetic rats by resistance training in the FHL, but not soleus muscle. Furthermore, resistance training decreased inflammatory cytokines in FHL skeletal muscle. On the other hand, Hsp70 and inflammatory cytokine protein levels were increased by training in adipose tissue. Also, significant positive correlations between inflammatory cytokines in adipose tissue and skeletal muscles with Hsp70 protein levels were observed. In conclusion, we found that in diabetic rats, resistance training decreased inflammatory cytokines and Hsp70 protein levels in fast skeletal muscle, increased adipose tissue inflammatory cytokines and Hsp70, and preserved FHL muscle mass. These results suggest that resistance training can maintain skeletal muscle mass in diabetes by changing inflammatory cytokines and stress factors such as Hsp70 in skeletal muscle and adipose tissue.

p38 mitogen-activated protein kinase and mitogen-activated protein kinase-activated protein kinase 2 (MK2) signaling in atrophic and hypertrophic denervated mouse skeletal muscle

Background

p38 mitogen-activated protein kinase has been implicated in both skeletal muscle atrophy and hypertrophy. T317 phosphorylation of the p38 substrate mitogen-activated protein kinase-activated protein kinase 2 (MK2) correlates with muscle weight in atrophic and hypertrophic denervated muscle and may influence the nuclear and cytoplasmic distribution of p38 and/or MK2. The present study investigates expression and phosphorylation of p38, MK2 and related proteins in cytosolic and nuclear fractions from atrophic and hypertrophic 6-days denervated skeletal muscles compared to innervated controls.

Methods

Expression and phosphorylation of p38, MK2, Hsp25 (heat shock protein25_rodent/27_human, Hsp25/27) and Hsp70 protein expression were studied semi-quantitatively using Western blots with separated nuclear and cytosolic fractions from innervated and denervated hypertrophic hemidiaphragm and atrophic anterior tibial muscles. Unfractionated innervated and denervated atrophic pooled gastrocnemius and soleus muscles were also studied.

Results

No support was obtained for a differential nuclear/cytosolic localization of p38 or MK2 in denervated hypertrophic and atrophic muscle. The differential effect of denervation on T317 phosphorylation of MK2 in denervated hypertrophic and atrophic muscle was not reflected in p38 phosphorylation nor in the phosphorylation of the MK2 substrate Hsp25. Hsp25 phosphorylation increased 3-30-fold in all denervated muscles studied. The expression of Hsp70 increased 3-5-fold only in denervated hypertrophic muscles.

Conclusions

The study confirms a differential response of MK2 T317 phosphorylation in denervated hypertrophic and atrophic muscles and suggests that Hsp70 may be important for this. Increased Hsp25 phosphorylation in all denervated muscles studied indicates a role for factors other than MK2 in the regulation of this phosphorylation.

Acute heat stress prior to downhill running may enhance skeletal muscle remodeling

Heat shock proteins (HSPs) are chaperones that are known to have important roles in facilitating protein synthesis, protein assembly and cellular protection. While HSPs are known to be induced by damaging exercise, little is known about how HSPs actually mediate skeletal muscle adaption to exercise. The purpose of this study was to determine the effects of a heat shock pretreatment and the ensuing increase in HSP expression on early remodeling and signaling (2 and 48 h) events of the soleus (Sol) muscle following a bout of downhill running. Male Wistar rats (10 weeks old) were randomly assigned to control, eccentric exercise (EE; downhill running) or heat shock + eccentric exercise (HS; 41°C for 20 min, 48 h prior to exercise) groups. Markers of muscle damage, muscle regeneration and intracellular signaling were assessed. The phosphorylation (p) of HSP25, Akt, p70s6k, ERK1/2 and JNK proteins was also performed. As expected, following exercise the EE group had increased creatine kinase (CK; 2 h) and mononuclear cell infiltration (48 h) compared to controls. The EE group had an increase in p-HSP25, but there was no change in HSP72 expression, total protein concentration, or neonatal MHC content. Additionally, the EE group had increased p-p70s6k, p-ERK1/2, and p-JNK (2 h) compared to controls; however no changes in p-Akt were seen. In contrast, the HS group had reduced CK (2 h) and mononuclear cell infiltration (48 h) compared to EE. Moreover, the HS group had increased HSP72 content (2 and 48 h), total protein concentration (48 h), neonatal MHC content (2 and 48 h), p-HSP25 and p-p70s6k (2 h). Lastly, the HS group had reduced p-Akt (48 h) and p-ERK1/2 (2 h). These data suggest that heat shock pretreatment and/or the ensuing HSP72 response may protect against muscle damage, and enhance increases in total protein and neonatal MHC content following exercise. These changes appear to be independent of Akt and MAPK signaling pathways.

Early response of heat shock proteins to functional overload of the soleus and plantaris in rats and mice

Heat shock proteins (HSPs) are important factors in the response of skeletal muscles to chronic increases or decreases in activation and loading. The purpose of this study was to compare species-, time- and muscle-dependent changes in protein expression of Hsp20, Hsp25, αB-crystallin, Hsp72 and Hsp90 in response to functional overload (FO) in rats and mice. We compared protein levels of Hsp20, Hsp25, αB-crystallin, Hsp72 and Hsp90 in soleus and plantaris in baseline conditions and following 0.5, 1, 2, 3 and 7 days (rats) or 3 and 7 days (mice) of FO. Baseline levels of all HSPs were higher in rat soleus than plantaris, whereas only baseline expression of Hsp20 was higher in mouse soleus than plantaris. Levels of Hsp72 and Hsp90 were higher in plantaris and soleus of FO than control mice and rats after 3 and 7 days of FO. Protein levels and phosphorylation of Hsp25 in mouse plantaris and soleus were higher than control levels after 3 and 7 days of FO, except for soleus at 3 days. αB-crystallin levels were higher in plantaris of FO than control mice after 3 and 7 days of FO and in FO than control rats after 7 days of FO. Heat shock protein 20 was the least responsive, increasing only in 7 day FO rat plantaris compared with control rats. Overall, the results demonstrate that levels of both large and small HSPs increase with FO, suggesting a contributory role during the compensatory hypertrophy response.

Heat stress increases myonuclear number and fiber size via satellite cell activation in rat regenerating soleus fibers

To investigate the effects of heat stress (hyperthermia) on muscle degeneration-regeneration, the soleus muscles of adult male Wistar rats were injected bilaterally with a single injection of bupivacaine. The rats were assigned to a sedentary control (Con), heat stress (Heat), bupivacaine-injected (BPVC), or bupivacaine-injected plus heat stress (BPVC+Heat) group. Heat stress was induced in the Heat and BPVC+Heat groups by immersion of the lower half of the body into water maintained at 42 ± 1°C for 30 min 48 h after the injection of bupivacaine and every other day during the following 1 or 2 wk. The soleus muscles in all groups were excised 24 h after the final bout of heat stress. Mean muscle weight, fiber cross-sectional area, myonuclear number, and heat shock protein 72 (Hsp72) and calcineurin protein levels were lower in the BPVC than in the Con or Heat groups at both time points. In contrast, several of these parameters in the BPVC+Heat group were not different or higher than in the Con or Heat groups at the 1- and/or 2-wk time points. The number of total and activated satellite cells, estimated by analyses of Pax7-negative, M-cadherin-negative, and MyoD-positive nuclei, was greater in BPVC+Heat than in all other groups. Combined, the results indicate that heat stress-related activation of satellite cells and upregulation of Hsp72 and calcineurin expression played important roles in the regeneration of the soleus fibers after bupivacaine injection.

Heat shock proteins and exercise: a primer

Heat shock proteins (HSPs) are, in general, prosurvival molecules within the cellular environment, and the overexpression of even just 1 family of HSPs can lead to protection against and improvements after a variety of stressors. Not surprisingly, a fertile area of study has grown out of efforts to exploit the innate biologic behaviour of HSPs. Exercise, because of the inherent physiologic stresses associated with it, is but 1 stimulus that can result in a robust increase in various HSPs in several tissues, not the least of which happen to be the heart and skeletal muscle. The purpose of this review is to introduce the reader to the major HSP families, the control of their expression, and some of their biologic functions, specifically with respect to the influence of exercise. Moreover, as the first in a series of reviews from a common symposium, we will briefly introduce the concepts presented by the other authors, which include the effects of different exercise paradigms on skeletal muscle HSPs in the adult and aged systems, HSPs as regulators of inflammation, and the ion channel stabilizing effects of HSPs.

Cellular adaptations in soleus muscle during recovery after hindlimb unloading

AIM

We used a model of chronic unloading followed by reloading to examine the apoptotic responses associated with soleus muscle atrophy and subsequent recovery.

METHODS

Male Wistar rats were subjected to hindlimb unloading (HU) for 2 weeks and subsequent reloading for 0, 3, 7 and 14 days. One-half of the HU-reloaded rats were administered cyclosporine A (CsA), a calcineurin (CaN) inhibitor.

RESULTS

There was fibre atrophy (73%) and a decrease in slow type I fibre/myosin heavy chain (MyHC) composition in the soleus muscle after 2 weeks of HU. Fibre size and type I MyHC composition recovered to near the age-matched control levels by recovery day 14 in non-treated, but not in CsA-treated, rats. Myonuclear number was lower and the number of apoptotic nuclei higher in 2-week HU than control rats. These values returned to control levels after 7 and 14 days of recovery, respectively, in both HU-recovery groups. After 2 weeks of HU, the levels of heat shock proteins (Hsp) 60 and 72, mitochondrial cytochrome c oxidase subunit IV (Cox IV), and peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1) proteins were lower than control. The levels of all of these proteins gradually increased to or above the control levels during cage recovery in both groups.

CONCLUSION

Our results indicate that apoptotic mechanisms are involved in the modulation of myonuclear number during chronic unloading and subsequent reloading. Furthermore, it appears that CaN is related to fibre size and phenotype adaptations, but not to apoptotic responses.

Thyroid hormone as a determinant of metabolic and contractile phenotype of skeletal muscle

Skeletal muscles are composed of several types of fibers with different contractile and metabolic properties. Genetic background and type of innervation of the fibers primarily determine these properties, but thyroid hormone (TH) is a powerful modulator of the fiber phenotype. The rates of contraction and relaxation are stimulated by TH, as are the energy consumption and heat production associated with activity. Quantitative and qualitative changes in substrate metabolism accommodate the increase in ATP turnover. Because of the total mass of skeletal muscle, these changes affect whole-body physiology. Although apparently straightforward, the phenotypic shifts induced by TH are highly complex and fiber specific. This review addresses the mechanisms by which TH may modulate fiber gene expression and discusses some of the implications of the TH-regulated changes in metabolic and contractile phenotype of skeletal muscle.

Time-dependent changes in caspase-3 activity and heat shock protein 25 after spinal cord transection in adult rats

Chronic reductions in muscle activation and loading are associated with decreased heat shock protein 25 (Hsp25) expression and phosphorylation (pHsp25) which, in turn, may contribute to elevated caspase-3-mediated muscle protein breakdown. Thus, the purpose of the present study was to determine whether there are any changes in Hsp25, pHsp25 and caspase-3 activity among rat muscles having different fibre type compositions and functions [soleus, adductor longus (AL), plantaris and tibialis anterior (TA)] at 0 (control), 1, 8 or 28 days after a complete spinal cord transection (ST). The Hsp25 levels were unaffected on days 1 and 8 in all muscles, except for a significant reduction on day 8 in plantaris. The Hsp25 levels were lower than control values in all muscles except TA on day 28. The pHsp25 levels were lower than control values after 8 and 28 days in plantaris and AL and after 28 days in soleus, but higher than control in TA after 8 and 28 days. Caspase-3 activity was higher in ST than control rats on day 8 in all muscles except TA. Caspase-3 activity was negatively correlated with muscle mass for all muscles. In plantaris, Hsp25 and pHsp25 were negatively correlated with caspase-3 activity and Hsp25 was correlated with muscle mass. These relationships were not observed in other muscles. Thus, the effects of ST on Hsp25 and caspase-3 are muscle specific and time dependent, factors that should be considered in developing any intervention to maintain muscle mass after a spinal cord injury.

Leptin downregulates heat shock protein-70 (HSP-70) gene expression in chicken liver and hypothalamus

Heat shock protein (HSP)-70 is expressed in normal and stressed cells but is highly stress-inducible. Although leptin has long been suggested to be involved in the regulation of stress response, its interaction with the HSP-70 gene is still unknown, under both unstressed and stressed conditions. The present study has aimed to investigate the effect of leptin on HSP-70 gene expression in normal chicken liver, hypothalamus, and muscle. Continuous infusion of recombinant chicken leptin (8 mug/kg per hour) at a constant rate of 3 ml/h for 6 h in 3-week-old broiler chickens significantly (P < 0.05) decreased food intake and HSP-70 mRNA levels in liver and hypothalamus, but not in muscle. In an attempt to discriminate between the effect of leptin and of leptin-reduced food intake on HSP-70 gene expression, we also evaluated the effect of food deprivation on the same cellular responses in two broiler chicken lines genetically selected for low (LL) or high (FL) abdominal fat pad size. Food deprivation for 16 h did not affect HSP-70 gene expression in any of the studied tissues indicating that the effect of leptin was independent of the inhibition of food intake. Regardless of the nutritional status, HSP-70 mRNA levels were significantly (P < 0.05) higher in the hypothalamus of FL compared with LL chickens consistent with higher mRNA levels for hypothalamic corticotropin-releasing factor. To assess, whether the effects of leptin were direct or indirect, we carried out in vitro studies. Leptin treatments did not affect HSP-70 mRNA levels in a leghorn male hepatoma cell line or quail myoblast cell line suggesting that the effect of leptin on HSP-70 gene expression is mediated through the central nervous system. Furthermore, HSP-70 gene expression was gender-dependent with significantly (P < 0.05) higher levels in male than in female chickens.

Modulation of HSP25 and TNF-alpha during the early stages of functional overload of a rat slow and fast muscle

Early events in response to abrupt increases in activation and loading with muscle functional overload (FO) are associated with increased damage and inflammation. Heat shock protein 25 (HSP25) may protect against these stressors, and its expression can be regulated by muscle loading and activation. The purpose of this study was to investigate the responses of HSP25, phosphorylated HSP25 (pHSP25), and tumor necrosis factor-alpha (TNF-alpha) during FO of the slow soleus and fast plantaris. We compared the HSP25 mRNA, HSP25 protein, pHSP25, and TNF-alpha responses in the soleus and plantaris after 0.5, 1, 2, 3, and 7 days of FO. HSP25 and pHSP25 were quantified in soluble and insoluble fractions. HSP25 mRNA increased immediately in both muscles and decreased with continued FO. However, HSP25 mRNA levels were consistently higher in the muscles of FO than control rats. In the soluble fraction, HSP25 increased in the plantaris after 2-7 days of FO with the greatest response at 3 and 7 days. The pHSP25 response to FO was greater in the plantaris than soleus at all points in the soluble fraction and at 0.5 days in the insoluble fraction. TNF-alpha levels in the plantaris, but not soleus, were higher than control at 0.5-2 days of FO. This may have contributed to the greater FO response in pHSP25 in the plantaris than soleus as TNF-alpha increased pHSP25 in C2C12 myotubes. These results suggest that the initial responses of pHSP25 and TNF-alpha to mechanical stress and inflammation associated with FO are greater in a fast than slow extensor muscle.

Slower skeletal muscle phenotypes are critical for constitutive expression of Hsp70 in overloaded rat plantaris muscle

Heat shock protein 72 (Hsp70) is constitutively expressed in rat hindlimb muscles, reportedly in proportion to their content of type I myosin heavy chain. This distribution pattern has been suggested to result from the higher recruitment and activity of such muscles and/or a specific relationship between myosin phenotype and Hsp70 content. To differentiate between these possibilities, the fiber-specific distribution of Hsp70 was examined in male Sprague-Dawley rat plantaris under control conditions, following a fast-to-slow phenotypic shift in response to surgically induced overload (O) and in response to O when the phenotypic shift was prevented by 3,5,3'-triiodo-dl-thyronine administration. Constitutive expression of Hsp70 was restricted to type I and IIa fibers in plantaris from control rats, and this fiber-specific pattern of expression was maintained following O of up to 28 days, although Hsp70 content in the O muscle doubled. When O (for 40 days) of the plantaris was combined with 3,5,3'-triiodo-dl-thyronine administration, despite typical hypertrophy in the overloaded plantaris, prevention of the normal phenotypic transformation also blocked the increased expression of Hsp70 observed in euthyroid controls. Collectively, these data suggest that chronic changes in constitutive expression of Hsp70 with altered contractile activity appear critically dependent on fast-to-slow phenotypic remodeling.