Parvalbumin Expression Is Downregulated in Rat Fast-Twitch Skeletal Muscles during Aging

Prolonged fasting followed by refeeding modifies proteome profile and parvalbumin expression in the fast-twitch muscle of pacu (Piaractus mesopotamicus)

Here, we analyzed the fast-twitch muscle of juvenile Piaractus mesopotamicus (pacu) submitted to prolonged fasting (30d) and refeeding (6h, 24h, 48h and 30d). We measured the relative rate of weight and length increase (RRI_length and RRI_weight), performed shotgun proteomic analysis and did Western blotting for PVALB after 30d of fasting and 30d of refeeding. We assessed the gene expression of igf-1, mafbx and pvalb after 30d of fasting and after 6h, 24h, 48h and 30d of refeeding. We performed a bioinformatic analysis to predict miRNAs that possibly control parvalbumin expression. After fasting, RRI_length, RRI_weight and igf-1 expression decreased, while the mafbx expression increased, which suggest that prolonged fasting caused muscle atrophy. After 6h and 24h of refeeding, mafbx was not changed and igf-1 was downregulated, while after 48h of refeeding mafbx was downregulated and igf-1 was not changed. After 30d of refeeding, RRI_length and RRI_weight were increased and igf-1 and mafbx expression were not changed. Proteomic analysis identified 99 proteins after 30d of fasting and 71 proteins after 30d of refeeding, of which 23 and 17, respectively, were differentially expressed. Most of these differentially expressed proteins were related to cytoskeleton, muscle contraction, and metabolism. Among these, parvalbumin (PVALB) was selected for further validation. The analysis showed that pvalb mRNA was downregulated after 6h and 24h of refeeding, but was not changed after 30d of fasting or 48h and 30d of refeeding. The Western blotting confirmed that PVALB protein was downregulated after 30d of fasting and 30d of refeeding. The downregulation of the protein and the unchanged expression of the mRNA after 30d of fasting and 30d of refeeding suggest a post-transcriptional regulation of PVALB. Our miRNA analysis predicted 444 unique miRNAs that may target pvalb. In conclusion, muscle atrophy and partial compensatory growth caused by prolonged fasting followed by refeeding affected the muscle proteome and PVALB expression.

Estrogen replacement improves skeletal muscle performance by increasing parvalbumin levels in ovariectomized rats

Muscle weakness is common during menopause. Effective estrogen replacement was hypothesized to prevent sarcopenia. This study aimed to investigate the estrogen level, estrogen receptors (α and β) immunoreactivities, muscle mass and functions, and parvalbumin (PV) levels in the extensor digitorum longus (EDL) and the gastrocnemius muscles of ovariectomized rats. Adult female Wistar rats (12 weeks old) were divided into five groups: sham-operated (SHAM), and ovariectomized (E0) groups that received 10 weeks of estrogen replacements of 0μg/kg (E0), 10μg/kg (E10), 20μg/kg (E20) and 40μg/kg (E40). The estrogen levels, ER α and ER β immunoreactivities, muscle fiber sizes and contractivities and the PV levels were reduced in the E0 group, but increased in all the estrogen replacement groups in both muscles. This study indicated that the reduction of estrogen levels led to a decrease of both ER α and ER β resulting in a decline in muscle mass and PV levels. The decrease of PV levels affected muscle performance, whereas estrogen replacement increased both the ER α and ER β. The increase in the PV levels may result in an improvement of muscle performance. This may explain one mechanism of estrogen on muscle mass and strength in estrogen dependent sarcopenia.

Parvalbumin gene transfer impairs skeletal muscle contractility in old mice

Sarcopenia is the progressive age-related loss of skeletal muscle mass associated with functional impairments that reduce mobility and quality of life. Overt muscle wasting with sarcopenia is usually preceded by a slowing of the rate of relaxation and a reduction in maximum force production. Parvalbumin (PV) is a cytosolic Ca(2+) buffer thought to facilitate relaxation in muscle. We tested the hypothesis that restoration of PV levels in muscles of old mice would increase the magnitude and hasten relaxation of submaximal and maximal force responses. The tibialis anterior (TA) muscles of young (6 month), adult (13 month), and old (26 month) C57BL/6 mice received electroporation-assisted gene transfer of plasmid encoding PV or empty plasmid (pcDNA3.1). Contractile properties of TA muscles were assessed in situ 14 days after transfer. In old mice, muscles with increased PV expression had a 40% slower rate of tetanic force development (p<0.01), and maximum twitch and tetanic force were 22% and 16% lower than control values, respectively (p<0.05). Muscles with increased PV expression from old mice had an 18% lower maximum specific (normalized) force than controls, and absolute force was `26% lower at higher stimulation frequencies (150-300 Hz, p<0.05). In contrast, there was no effect of increased PV expression on TA muscle contractile properties in young and adult mice. The impairments in skeletal muscle function in old mice argue against PV overexpression as a therapeutic strategy for ameliorating aspects of contractile dysfunction with sarcopenia and help clarify directions for therapeutic interventions for age-related changes in skeletal muscle structure and function.

Treatment with a corticotrophin releasing factor 2 receptor agonist modulates skeletal muscle mass and force production in aged and chronically ill animals

Background

Muscle weakness is associated with a variety of chronic disorders such as emphysema (EMP) and congestive heart failure (CHF) as well as aging. Therapies to treat muscle weakness associated with chronic disease or aging are lacking. Corticotrophin releasing factor 2 receptor (CRF2R) agonists have been shown to maintain skeletal muscle mass and force production in a variety of acute conditions that lead to skeletal muscle wasting.

Hypothesis

We hypothesize that treating animals with a CRF2R agonist will maintain skeletal muscle mass and force production in animals with chronic disease and in aged animals.

Methods

We utilized animal models of aging, CHF and EMP to evaluate the potential of CRF2R agonist treatment to maintain skeletal muscle mass and force production in aged animals and animals with CHF and EMP.

Results

In aged rats, we demonstrate that treatment with a CRF2R agonist for up to 3 months results in greater extensor digitorum longus (EDL) force production, EDL mass, soleus mass and soleus force production compared to age matched untreated animals. In the hamster EMP model, we demonstrate that treatment with a CRF2R agonist for up to 5 months results in greater EDL force production in EMP hamsters when compared to vehicle treated EMP hamsters and greater EDL mass and force in normal hamsters when compared to vehicle treated normal hamsters. In the rat CHF model, we demonstrate that treatment with a CRF2R agonist for up to 3 months results in greater EDL and soleus muscle mass and force production in CHF rats and normal rats when compared to the corresponding vehicle treated animals.

Conclusions

These data demonstrate that the underlying physiological conditions associated with chronic diseases such as CHF and emphysema in addition to aging do not reduce the potential of CRF2R agonists to maintain skeletal muscle mass and force production.

Studies of complex biological systems with applications to molecular medicine: the need to integrate transcriptomic and proteomic approaches

Omics approaches to the study of complex biological systems with potential applications to molecular medicine are attracting great interest in clinical as well as in basic biological research. Genomics, transcriptomics and proteomics are characterized by the lack of an a priori definition of scope, and this gives sufficient leeway for investigators (a) to discern all at once a globally altered pattern of gene/protein expression and (b) to examine the complex interactions that regulate entire biological processes. Two popular platforms in "omics" are DNA microarrays, which measure messenger RNA transcript levels, and proteomic analyses, which identify and quantify proteins. Because of their intrinsic strengths and weaknesses, no single approach can fully unravel the complexities of fundamental biological events. However, an appropriate combination of different tools could lead to integrative analyses that would furnish new insights not accessible through one-dimensional datasets. In this review, we will outline some of the challenges associated with integrative analyses relating to the changes in metabolic pathways that occur in complex pathophysiological conditions (viz. ageing and altered thyroid state) in relevant metabolically active tissues. In addition, we discuss several new applications of proteomic analysis to the investigation of mitochondrial activity.

Influence of aging and long-term swimming exercise on parvalbumin distribution in rat hearts

Parvalbumin (PV), which is a small (12kDa) cytoplasmic calcium-binding protein, has been implicated in mediating relaxation in cardiac myocytes. The influence of aging and exercise on the distribution of PV in rat heart was investigated. Male Wistar rats aged 3, 6, 12 and 18-months were divided into sedentary and exercise groups. The exercise group underwent exercise in the form of regular swimming for 6 months. The hearts were processed for immunohistochemistry and Western blotting. The intensity of PV immunoreactivity was strong in the 9 and 12-month hearts and decreased in the 18-month hearts. The smallest amount was detected in the 24-month rat hearts when compared to those of the 9, 12 and 18-month rat hearts. Significantly less PV was detected in the 18 and 24-month hearts compared to the 12-month rat hearts (P<0.05). The intensity of PV immunoreactivity was considerably stronger in hearts of the 9, 12 and 18-months exercised rats than in hearts of age-matched sedentary rats. However, in the hearts of 24-month rats, immunoreactivity was only slightly stronger in the exercised rats in comparison with those of sedentary rats. A significant increase of PV detection in hearts was found in the exercised rats in comparison with sedentary rats in the 9 (P<0.05) and 18-month samples (P<0.01). Our data indicate that PV is down-regulated in the rat heart during aging. In addition, our data indicate that long-term swimming exercise could induce an increase of PV expression.

Diminished contraction-induced intracellular signaling towards mitochondrial biogenesis in aged skeletal muscle

The intent of this study was to determine whether aging affects signaling pathways involved in mitochondrial biogenesis in response to a single bout of contractile activity. Acute stimulation (1 Hz, 5 min) of the tibialis anterior (TA) resulted in a greater rate of fatigue in old (36 month), compared to young (6 month) F344XBN rats, which was associated with reduced ATP synthesis and a lower mitochondrial volume. To investigate fiber type-specific signaling, the TA was sectioned into red (RTA) and white (WTA) portions, possessing two- to 2.5-fold differences in mitochondrial content. The expression and contraction-mediated phosphorylation of p38, MKK3/6, CaMKII and AMPKalpha were assessed. Kinase protein expression tended to be higher in fiber sections with lower mitochondrial content, such as the WTA, relative to the RTA muscle, and this was exaggerated in tissues from senescent, compared to young animals. At rest, kinase activation was generally similar between young and old animals, despite the age-related variations in mitochondrial volume. In response to contractile activity, age did not influence the signaling of these kinases in the high-oxidative RTA muscle. However, in the low-oxidative WTA muscle, contraction-induced kinase activation was attenuated in old animals, despite the greater metabolic stress imposed by contractile activity in this muscle. Thus, the reduction of contraction-evoked kinase phosphorylation in muscle from old animals is fiber type-specific, and depends on factors which are, in part, independent of the metabolic milieu within the contracting fibers. These findings imply that the downstream consequences of kinase signaling are reduced in aging muscle.

A Ca(2+)-binding protein with numerous roles and uses: parvalbumin in molecular biology and physiology

Parvalbumins (PVs) are acidic, intracellular Ca(2+)-binding proteins of low molecular weight. They are associated with several Ca(2+)-mediated cellular activities and physiological processes. It has been suggested that PV might function as a "Ca2+ shuttle" transporting Ca2+ from troponin-C (TnC) to the sarcoplasmic reticulum (SR) Ca2+ pump during muscle relaxation. Thus, PV may contribute to the performance of rapid, phasic movements by accelerating the contraction-relaxation cycle of fast-twitch muscle fibers. Interestingly, PVs promote the generation of power stroke in fish by speeding up the rate of relaxation and thus provide impetus to attain maximal sustainable speeds. However, immunological monitoring of diverse tissues demonstrated that PVs are also present in non-muscle cells. The axoplasmic transport and various intracellular secretory mechanisms including the endocrine secretions seem to be controlled by the Ca2+ regulation machinery. Any defect in the Ca2+ handling apparatus may cause several clinical problems; for instance, PV deficiency alters the neuronal activity, a key mechanism leading to epileptic seizures. Moreover, atypical relaxation of the heart results in diastolic dysfunction, which is a major cause of heart failure predominantly among the aged people. PV may offer a unique potential to correct defective relaxation in energetically compromised failing hearts through PV gene transfer. Consequently, PV gene transfer may present a new therapeutic approach to correct cellular disturbances in Ca2+ signaling pathways of diseased organs. Hence, PVs appear to be amazingly useful candidate proteins regulating a variety of cellular functions through action on Ca2+ flux management.

Subcellular proteomics of mice gastrocnemius and soleus muscles

A proteomics characterization of mice soleus and gastrocnemius white portion skeletal muscles was performed using nuclear, mitochondrial/membrane, and cytosolic subcellular fractions. The proposed methodology allowed the elimination of the cytoskeleton proteins from the cytosolic fraction and of basic proteins from the nuclear fraction. The subsequent protein separation by two-dimensional gel electrophoresis prior to mass spectrometry analysis allowed the detection of more than 600 spots in each muscle. In the gastrocnemius muscle fractions, it was possible to identify 178 protein spots corresponding to 108 different proteins. In the soleus muscle fractions, 103 different proteins were identified from 253 positive spot identifications. A bulk of cytoskeleton proteins such as actin, myosin light chains, and troponin were identified in the nuclear fraction, whereas mainly metabolic enzymes were detected in the cytosolic fraction. Transcription factors and proteins associated with protein biosynthesis were identified in skeletal muscles for the first time by proteomics. In addition, proteins involved in the mitochondrial redox system, as well as stress proteins, were identified. Results confirm the potential of this methodology to study the differential expressions of contractile proteins and metabolic enzymes, essential for generating functional diversity of muscles and muscle fiber types.

Up-regulation of parvalbumin expression in newborn and adult rat heart

Parvalbumin (PV), a cytoplasmic calcium-binding protein, functions as a relaxing factor and has recently been detected in rat heart. Developmental changes in PV localization and expression were investigated in the heart of Wistar rats at different ages. Ten hearts from newborn, 3-month-old (young), 6-month-old (young adult), and 12-month-old (adult) rats were processed for immunohistochemistry and Western blot assay. PV was detected in hearts of all the age groups of the rats from newborn to 12-month-old by both immunohistochemistry and Western blotting. A variable distribution of PV immunoreactivity was present in newborn cardiac myocytes. In the 3-, 6-, and 12-month-old rat hearts, identical PV immunoreactivity was found in all cardiac myocytes and the intensity of PV immunoreactivity increased with increasing age. By using Western blotting, it was found that the expression of PV was low in the newborn rat heart and increased with increasing age. The presence of PV may correlate with the physiological age, and possibly serves to maintain proper relaxation of the cardiac myocytes to cope with an increasing workload of the heart during body growth.

Fiber type-related changes in rat skeletal muscle calcium homeostasis during aging and restoration by growth hormone

The mechanisms by which aging induces muscle impairment are not well understood yet. We studied the impact of aging on Ca2+ homeostasis in the slow-twitch soleus and the fast-twitch extensor digitorum longus (EDL) muscles of aged rats by using the fura-2 fluorescent probe. In both muscles aging increases the resting cytosolic calcium concentration ([Ca2+]i). This effect was independent on calcium influx since a reduced resting permeability of sarcolemma to divalent cations was observed in aged muscles likely due to a reduced activity of leak channels. Importantly the effects of aging on resting [Ca2+]i, fiber diameter, mechanical threshold and sarcolemmal resting conductances were less pronounced in the soleus muscle, suggesting that muscle impairment may be less dependent on [Ca2+]i in the slow-twitch muscle. The treatment of aged rats with growth hormone restored the resting [Ca2+]i toward adult values in both muscles. Thus, an increase of resting [Ca2+]i may contribute to muscle weakness associated with aging and may be considered for developing new therapeutic strategies in the elderly.

2-D protein maps of rat gastrocnemius and soleus muscles: A tool for muscle plasticity assessment

Functional characterization of muscle fibers relies on ATPase activity and on differential measurements of metabolic proteins, including mitochondrial and glycolytic enzymes, glucose, lactate and lactic acid transporters, calcium cycling proteins and components of the contractile machinery. The recent introduction of microarray technology has enabled detailed gene expression studies under different physiological and pathological conditions, thus generating novel hypotheses on muscle function. However, microarray approaches are limited by the incomplete genome coverage of currently available chips, and by poor correlation between mRNA concentration and protein expression level. We have used 2-DE and MS to build a reference map of proteins from rat mixed gastrocnemius and soleus muscle, and to assess qualitative and quantitative differences in protein distribution between these two functionally dissimilar muscles. More than 800 spots on each gel were detected by silver staining, of which 167 were excised, digested in-gel with trypsin and analyzed by ESI-MS/MS. One hundred and twenty eight distinct gene products were identified, including metabolic, transport and contractile proteins. Forty one spots displayed differences in relative expression level between mixed gastrocnemius and soleus samples. These data not only enable differentiation of functionally distinct slow-twitch and fast-twitch fiber types, but also provide tools for investigating muscle plasticity in response to physiological and environmental conditions such as aging or hypoxia.

Proteomic analysis of rat laryngeal muscle following denervation

Laryngeal muscle atrophy induced by nerve injury is a major factor contributing to the disabling symptoms associated with laryngeal paralysis. Alterations of global proteins in rat laryngeal muscle following denervation were, therefore, studied using proteomic techniques. Twenty-eight adult Sprague-Dawley rats were divided into normal control and denervated groups. The thyroarytenoid (TA) muscle was excised 60 days after right recurrent laryngeal nerve was resected. Protein separation and identification were preformed using 2-DE and MALDI-MS with database search. Forty-four proteins were found to have significant alteration in expression level after denervation. The majority of these proteins (57%), most of them associated with energy metabolism, cellular proliferation and differentiation, signal transduction and stress reaction, were decreased levels of expression in denervated TA muscle. The remaining 43% of the proteins, most of them involved with protein degradation, immunoreactivity, injury repair, contraction, and microtubular formation, were found to have increased levels of expression. The protein modification sites by phosphorylation were detected in 22% of the identified proteins that presented multiple-spot patterns on 2-D gel. Significant changes in protein expression in denervated laryngeal muscle may provide potential therapeutic strategies for the treatment of laryngeal paralysis.

Postmetamorphic changes in parvalbumin expression in the hindlimb skeletal muscle of the bullfrog, Rana catesbeiana

Anuran amphibians, animals that spend a terrestrial life after metamorphosis, exhibit a marked development of hindlimbs during and after metamorphosis. In order to see whether changes occur in the muscle protein components in the course of postmetamorphic development, we subjected gastrocnemius muscle extracts from growing froglets to two-dimensional electrophoresis (2DE). As a result, we found two proteins to undergo a change in level. One spot, indicating a molecular mass of approximately 12 kDa and an isoelectric point (pI) of 5.0 first became detectable at 45 days after metamorphosis. Another spot, corresponding to a protein of 11 kDa and pI 4.8, was prominent until the former spot appeared. N-terminal amino acid sequence analysis and comparison of the spots with those of parvalbumin (PA) revealed that these two proteins were PA alpha and PA beta. Northern blot analysis using PA alpha and PA beta cDNAs as probes revealed that the PA beta mRNA level declined whereas that of PA alpha mRNA rose as the frogs grew.

Proteomic analysis of striated muscle

The techniques collectively known as proteomics are useful for characterizing the protein phenotype of a particular tissue or cell as well as quantitatively identifying differences in the levels of individual proteins following modulation of a tissue or cell. In the area of striated muscle research, proteomics has been a useful tool for identifying qualitative and quantitative changes in the striated muscle protein phenotype resulting from either disease or physiological modulation. Proteomics is useful for these investigations because many of the changes in the striated muscle phenotype resulting from either disease or changes in physiological state are qualitative and not quantitative changes. For example, modification of striated muscle proteins by phosphorylation and proteolytic cleavage are readily observed using proteomic technologies while these changes would not be identified using genomic technology. In this review, I will discuss the application of proteomic technology to striated muscle research, research designed to identify key protein changes that are either causal for or markers of a striated muscle disease or physiological condition.