Biomedical subjects

LaDora V Thompson

Publications and source records attributed to LaDora V Thompson.

17 recordsLinked to original sources

PubMed2006

Oxidative stress, mitochondria and mtDNA-mutator mice.

The oxidative stress theory of aging, an expansion of the mitochondrial theory of aging, is based around the idea of a vicious cycle, in which somatic mutations of mitochondrial DNA (mtDNA) provoke respiratory chain dysfunction leading to enhanced ROS production and in turn to the accumulation of further mtDNA mutations. Mitochondrial dysfunction and mtDNA mutations are amplified during the course of aging. Recently, results obtained from mtDNA-mutator mice further strengthen the role of mitochondria in the aging process. However, lack of increased oxidative stress in the mtDNA-mutator mice raises doubts in the direct connection of mtDNA mutations with increased ROS production, challenging the oxidative stress theory of aging. The purpose of this short review is to highlight several studies that provide direct evidence that accelerated aging is linked to mtDNA mutations, without an increase in oxidative damage.

Aging↗

PubMed2006

Effects of hindlimb unweighting and aging on rat semimembranosus muscle and myosin.

We tested the hypothesis that lower specific force (force/cross-sectional area) generated by type II fibers from hindlimb-unweighted rats resulted from structural changes in myosin (i.e., a change in the ratio of myosin cross bridges in the weak- and strong-binding state during contraction). In addition, we determined whether those changes were age dependent. Permeabilized semimembranosus muscle fibers from young adult and aged rats, some of which were hindlimb unweighted for 3 wk, were studied for Ca(2+)-activated force generation and maximal unloaded shortening velocity. Fibers were also spin labeled specifically at myosin Cys707 to assess the structural distribution of myosin during maximal isometric contraction using electron paramagnetic resonance spectroscopy. Myosin heavy chain isoform (MHC) expression and the ratio of MHC to actin were evaluated in each fiber. Fibers from the unweighted rats generated 34% less specific force than fibers from weight-bearing rats (P < 0.001), independent of age. Electron paramagnetic resonance analyses showed that the fraction of myosin heads in the strong-binding structural state during contraction was 11% lower in fibers from the unweighted rats (P = 0.019), independent of age. More fibers from unweighted rats coexpressed MHC IIB-IIX compared with fibers from weight-bearing rats (P = 0.049). Unweighting induced a slowing of maximal unloaded shortening velocity and an increase in the ratio of MHC to actin in fibers from young rats only. These data indicate that altered myosin structural distribution during contraction and a preferential loss of actin contribute to unweighting-induced muscle weakness. Furthermore, the age of the rat has an influence on some parameters of changes in muscle contractility that are induced by unweighting.

Adaptation, Physiological↗

PubMed2006

Protein nitration with aging in the rat semimembranosus and soleus muscles.

On the basis of the accelerated age-related effects in type II muscle, we hypothesized that with aging the semimembranosus (type II) muscle would accumulate a greater amount of oxidized proteins compared to proteins in the soleus (type I) muscle. In this study, 3-nitrotyrosine (3-NT) was used as a stable marker of protein oxidative damage. The presence of 3-NT was evaluated in muscles from young adult, old, and very old Fischer 344 rats to provide an indication of the time course of muscle protein oxidative damage. A significant age-associated increase in nitrotyrosine-modified proteins was observed. The modified proteins identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry include the sarcoplasmic reticulum Ca(+2)-ATPase, aconitase, beta-enolase, triosephosphate isomerase, and carbonic anhydrase III. These proteins, involved in metabolism and calcium homeostasis, exhibited an age-dependent increase in 3-NT content in both muscles. However, significant levels of 3-NT modification were present at an earlier age in the semimembranosus muscle.

Aging↗

PubMed2005

On-column labeling for capillary electrophoretic analysis of individual mitochondria directly sampled from tissue cross sections.

This technical note reports on a new procedure to on-column-label organelles sampled from a tissue cross section into a fused silica capillary. These organelles are then analyzed by capillary electrophoresis with postcolumn laser-induced fluorescence detection. In this procedure, the fluorescent label does not come in contact with the tissue, which facilitates visualization of the sampled tissue cross section. In addition, on-column labeling allows for better control of the reaction time and fluorescent label concentrations. As a proof-of-principle, we show results of mitochondria from rat gastrocnemius muscle cross sections that were on-column-labeled with 10-N-nonyl acridine orange (NAO), a mitochondrion-specific probe, and compare them with results for NAO in-tissue labeling of the same tissue. The new organelle labeling procedure reported here may easily be extended to the analysis of individual organelles in other biological samples and may become a valuable tool in studies investigating the role of mitochondria in muscle aging and exercise physiology.

Anatomy, Cross-Sectional↗

PubMed2005

Effects of endurance exercise-training on single-fiber contractile properties of insulin-treated streptozotocin-induced diabetic rats.

The purpose of this study was to characterize the contractile properties of individual skinned muscle fibers from insulin-treated streptozotocin-induced diabetic rats after an endurance exercise training program. We hypothesized that single-fiber contractile function would decrease in the diabetic sedentary rats and that endurance exercise would preserve the function. In the study, 28 rats were assigned to either a nondiabetic sedentary, a nondiabetic exercise, a diabetic sedentary, or a diabetic exercise group. Rats in the diabetic groups received subcutaneous intermediate-lasting insulin daily. The exercise-trained rats ran on a treadmill at a moderate intensity for 60 min, five times per week. After 12 wk, the extensor digitorum longus and soleus muscles were dissected. Single-fiber diameter, Ca(2+)-activated peak force, specific tension, activation threshold, and pCa(50) as well as the myosin heavy chain isoform expression (MHC) were determined. We found that in MHC type II fibers from extensor digitorum longus muscle, diameters were significantly smaller from diabetic sedentary rats compared with nondiabetic sedentary rats (P < 0.001). Among the nondiabetic rats, fiber diameters were smaller with exercise (P = 0.038). The absolute force-generating capacity of single fibers was lower in muscles from diabetic rats. There was greater specific tension (force normalized to cross-sectional area) by fibers from the rats that followed an endurance exercise program compared with sedentary. From the results, we conclude that alterations in the properties of contractile proteins are not implicated in the decrease in strength associated with diabetes and that endurance-exercise training does not prevent or increase muscle weakness in diabetic rats.

Adaptation, Physiological↗

PubMed2005

Altered proteasome structure, function, and oxidation in aged muscle.

The proteasome is the main protease for degrading oxidized proteins. We asked whether altered proteasome function contributes to the accumulation of oxidized muscle proteins with aging. Proteasome structure, function, and oxidation state were compared in young and aged F344BN rat fast-twitch skeletal muscle. In proteasome-enriched homogenates from aged muscle, we observed a two- to threefold increase in content of the 20S proteasome that was due to a corresponding increase in immunoproteasome. Content of the regulatory proteins, PA700 and PA28, relative to the 20S were reduced 75% with aging. Upon addition of exogenous PA700, there was a twofold increase in peptide hydrolysis in aged muscle, suggesting the endogenous content of PA700 is inadequate for complete activation of the 20S. Measures of catalytic activity showed a 50% reduction in specific activity for proteasome-enriched homogenates with aging. With purification of the 20S, proteasome specific activity was equivalent between ages, indicating that endogenous regulators inhibit proteasome in aged muscle. Significantly less degradation of oxidized calmodulin by the 20S from aged muscle was observed. Partial rescue of activity for aged 20S by DTT implies oxidation of functionally significant cysteines. These results demonstrate significant age-related changes in proteasome structure, function, and oxidation state that could inhibit removal of oxidized proteins.

Aging↗

PubMed2005

Age-related differences in the adaptive potential of type I skeletal muscle fibers.

This study was designed to investigate whether the relationship of fiber size and force is maintained with aging and inactivity. We hypothesized that fiber size and fiber force-generating capacity would decrease in parallel, thus resulting in no change in specific force with either age or inactivity. Thirty male Fischer 344/Brown Norway F1 hybrid rats, 6-23-month old (young adult), 24-33-month old (middle-aged) and 34-40 month old (old) were hindlimb unweighted for 14 days. Single permeabilized type I fibers from the soleus and gastrocnemius muscles were evaluated for size and contractile function. The diameter of the fibers from the soleus muscle declined with age and unweighting. In contrast, the fibers from the gastrocnemius showed no age-related atrophy. In both the soleus and gastrocnemius, there was a significant decrease in the force generation with age and unweighting. When comparing size and peak absolute force in the type I fibers from control young and middle-aged animals a positive relationship was observed whereas no significant relationship between size and peak absolute force was observed in the old animals. Following unweighting, fibers from young and middle aged rats showed a significant relationship between force and size. Fibers from old animals did not exhibit a relationship between size and force following unweighting. These results suggest aged skeletal muscle has an attenuated ability to adapt to inactivity by altering its size in response to inactivity.

Adaptation, Physiological↗

PubMed2005

Adult and developmental myosin heavy chain isoforms in soleus muscle of aging Fischer Brown Norway rat.

Fiber type shifts in aging skeletal muscle have been studied with myofibrillar ATPase histochemistry and gel electrophoresis, but less commonly with immunohistochemistry. Immunohistochemical study of myosin heavy chains (MHCs) in single myofibers yields additional information about aged skeletal muscle. Furthermore, many studies of aging rodent skeletal muscle have been performed on fast-MHC-predominant muscle and in several different strains. The aim of this study was to evaluate immunohistochemically MHC characteristics in the slow-MHC-predominant soleus muscle in the Fischer Brown Norway F1 hybrid aging rat (FBN). Three age groups of FBN rats were studied: 12 months, 30 months, and 36 months. Soleus muscles were excised, quick-frozen, and stained immunohistochemically for slow, fast, developmental, and neonatal MHC isoforms. Cross-sections were evaluated for the number and cross-sectional areas of fibers expressing each isoform. Single myofibers in soleus muscles of the aged rats showed significantly greater amounts of coexpression of slow and fast MHC than did younger animals. This change began by 30 months of age, but did not reach statistical significance until 36 months of age. The soleus from 36-month-old rats also expressed greater amounts of developmental MHC than did the other groups. These developmental MHC-positive myofibers also coexpressed either slow or slow and fast MHC. The age-related increase in MHC coexpression of slow with fast isoforms may indicate a fiber type shift suggestive of denervation that outpaces reinnervation. The developmental MHC-positive fibers provide evidence of ongoing myofiber remodeling in the oldest rats in the midst of the fiber degeneration of aging.

Aging↗

PubMed2005

Myosin heavy chain isoform immunolabelling in diabetic rats with peripheral neuropathy.

This study evaluated mature and immature myosin heavy chain (MHC) isoform immunolocalisation in soleus muscle of diabetic rats with documented motor neuropathy. Sprague Dawley rats were assigned to one of three groups: control (C), diabetic with insulin (DI), or diabetic without insulin (DNI). Twelve weeks after diabetes induction, soleus muscles were excised and quick-frozen. Cross-sections were labelled immunohistochemically for slow, fast, developmental and neonatal MHC isoforms to determine fiber-type composition. Fiber cross-sectional areas were determined morphometrically. Results revealed that DNI and DI muscles contained greater percentages of myofibers positive for fast MHC compared with controls. DNI animals also showed a lower percentage of myofibers positive for slow MHC compared to the DI group. The number of fibers immunolabelled for developmental MHC isoforms was greater in DNI animals than in the other groups. The differences in slow and fast MHC-labelling appear to indicate a condition of altered neuromuscular activity affecting the diabetic muscles. The increase in developmental MHC-labelling in the DNI muscles could indicate myofiber regeneration or reinnervation that would be more pronounced in the DNI animals in context of their more severe neuropathy. Insulin appeared to influence muscle fiber cross-sectional area and possibly fiber-type grouping frequency; the potential mechanism for these effects was not elucidated.

Animals↗

PubMed2005

Age-related decline in actomyosin function.

To understand the molecular basis of the functional decline in aging muscle, we examined the functional (actomyosin ATPase) and chemical (cysteine content) changes in actin and myosin purified from the muscles of young (4- to 12-month-old) and old (27- to 35-month-old) Fisher 344 rats. Using the soluble, catalytically active myosin fragment, heavy meromyosin (HMM), we determined the maximum rate (V(max)) and actin concentration at half V(max) (K(m)) of the actomyosin ATPase, using four combinations of actin and HMM from old and young rats. V(max) and K(m) were significantly lower when both actin and HMM were obtained from old rats than when both proteins were obtained from young rats. The number of reactive cysteines in HMM significantly decreased with age, but no change was detected in the number of reactive cysteines in actin. We conclude that aging results in chemical changes in myosin (probably oxidation of cysteines) that have inhibitory effects on the actin-activated myosin ATPase.

Actins↗

PubMed2004

Altered proteasome function and subunit composition in aged muscle.

Myofibrillar protein degradation is mediated through the ubiquitin-proteasome pathway. To investigate if altered proteasome activity plays a role in age-related muscle atrophy, we examined muscle size and proteasome function in young and aged F344BN rats. Significant age-related muscle atrophy was confirmed by the 38% decrease in cross-sectional area of type 1 fibers in soleus muscle. Determination of proteasome function showed hydrolysis of fluorogenic peptides was equivalent between ages. However, when accounting for the 3-fold increase in content of the 20S catalytic core in aged muscle, the lower specific activity suggests a functional loss in individual proteins with aging. Comparing the composition of the catalytic beta-subunits showed an age-related 4-fold increase in the cytokine-inducible subunits, LMP2 and LMP7. Additionally, the content of the activating complexes, PA28 and PA700, relative to the 20S proteasome was reduced 50%. These results suggest significant alterations in the intrinsic activity, the percentage of immunoproteasome, and the regulation of the 20S proteasome by PA28 and PA700 in aged muscle.

Aging↗

PubMed2004

Myofibrillar myosin ATPase activity in hindlimb muscles from young and aged rats.

We tested the hypothesis that Ca(2+)-activated myosin ATPase activity is lower in muscles of aged rats relative to muscles of young rats, independent of changes in myosin isoform expression. Myofibrils were prepared from permeabilized fibers of soleus, plantaris, and semimembranosus muscles of young (8-12 months) and aged (32-38 months) F344 x BN rats and assayed for resting myosin ATPase, Ca(2+)-activated myosin ATPase, and myosin heavy chain (MHC) and myosin light chain (MLC) isoform compositions. Resting myosin ATPases were not affected by age in any muscle (P > or = 0.42). Ca(2+)-activated myosin ATPases of soleus and plantaris myofibrils were not affected by age (P > or = 0.31) but were 16% lower in semimembranosus myofibrils from aged rats (0.448 +/- 0.019 micromol P(i)/min/mg) compared to young rats (0.533 +/- 0.031 micromol P(i)/min/mg; P = 0.03). Correspondingly, maximal unloaded shortening velocity of single semimembranosus fibers from aged rats was slow (4.6 +/- 0.2 fiber lengths/s) compared with fibers from young rats (5.8 +/- 0.3 fiber lengths/s; P < 0.01). No age-related changes in MHC or regulatory MLC isoforms were detected in any muscle (P > or = 0.08) but changes in the essential MLC occurred in plantaris and semimembranosus muscles. The data indicate that Ca(2+)-activated myosin ATPase activity is reduced with age in semimembranosus muscle, independent of age-related changes in MHC isoform expression, and is one mechanism contributing to age-related slowing of contraction in that muscle.

Aging↗

PubMed2004

The effects of non-weight bearing on skeletal muscle in older rats: an interrupted bout versus an uninterrupted bout.

Age-related changes in skeletal muscle, in combination with bed rest, may result in a poorer rehabilitation potential for an elderly patient. The purpose of this study was to determine the effects of non-weight bearing (hind limb unweighting [HU]) on the soleus and extensor digitorum longus (EDL) in older rats. Two non-weight bearing conditions were used: an uninterrupted bout of HU and an interrupted bout of HU. Twenty-one rats were randomly placed into 1 of 3 groups: control, interrupted HU (2 phases of 7 days of HU, separated by a 4-day weight-bearing phase) and an uninterrupted HU (18 uninterrupted days of HU). Following non-weight bearing, the soleus and EDL muscles were removed. Fiber type identification was performed by myofibrillar ATPase and cross-sectional area was determined. The findings suggest that any period of non-weight bearing leads to a decrease in muscle wet weight (19%-45%). Both type I and type II fibers of the soleus showed atrophy (decrease in cross-sectional area, 35%-44%) with an uninterrupted bout of non-weight bearing. Only the type II fibers of the soleus showed recovery with an interrupted bout of weight bearing. In the EDL, type II fibers were more affected by an uninterrupted bout of non-weight bearing (15% decrease in fiber size) compared to the type I fibers. EDL type II fibers showed more atrophy with interrupted bouts of non-weight bearing than with a single bout (a 40% compared to a 15% decrease). This study shows that initial weight bearing after an episode of non-weight bearing may be damaging to type II fibers of the EDL.

Adenosine Triphosphatases↗

PubMed2003

Muscle activity and aging affect myosin structural distribution and force generation in rat fibers.

The purpose of this study was to determine whether increased muscle activity could reverse myosin structural alterations that occur in aged rat muscle and whether those alterations could be induced in young rat muscle by decreased activity. Semimembranosus muscle activity was increased by electrical stimulation (200-ms trains, 154 Hz, 5 V) through a nerve cuff on the tibial branch of the ischiatic nerve. The protocol consisted of 5 sets of 6-10 maximal isometric contractions performed twice per week for 4 or 8-10 wk. Decreased muscle activity was induced by denervation of the semimembranosus muscle for 2 or 4 wk. Semimembranosus fibers were then studied for Ca(2+)-activated force generation. Fibers were also spin labeled on the myosin catalytic domain and studied using electron paramagnetic resonance (EPR) spectroscopy to assess myosin structural distribution. Increased muscle activity for 4 and 8-10 wk in approximately 32-mo-old rats resulted in -16 and +4% changes in specific tension, respectively (P < 0.01). EPR spectra showed that the fraction of myosin heads in the strong-binding structural state during contraction was reduced at 4 wk (0.241 +/- 0.020 vs. 0.269 +/- 0.018, P = 0.046) but returned to normal by 8-10 wk (P = 0.67). Decreased muscle activity for 2 and 4 wk in approximately 9-mo-old rats resulted in 23 and 34% reductions, respectively, in specific tension; EPR spectra showed 16 and 35% decreases in strong-binding myosin (P < 0.01). These data support the hypothesis that changes in muscle activity affect muscle strength, at least in part through alterations in myosin structure and function.

Aging↗

PubMed2002

Enzymatic alterations in single type IIB skeletal muscle fibers with inactivity and exercise in 12- and 30-month-old rats.

The purpose of the present study was to examine the effects of aging, inactivity and weight-bearing exercise on fast-twitch single Type IIB skeletal muscle fibers from the superficial region of the lateral head of the gastrocnemius (Type IIB fibers). Specifically, this study compared the biochemical properties of Type IIB fibers after 7 days of hindlimb unweighting (HU), 7 days of HU with intermittent weight-bearing (HU-Ex), and cage control (C) from adult and aged Fischer 344 Brown Norway F1 Hybrid rats (12- and 30-month old). Biochemical measurements included total lactate dehydrogenase (LDH) and beta-hydroxy-acyl-coenzyme A dehydrogenase activities (BHAD), expressed in nmoles/microg/hr dry weight. Fiber-typing for myosin heavy chain isoform was determined by SDS-PAGE. With age, LDH activity in Type IIB fibers decreased from 52.0 +/- 3.4 nmoles/microg/hr (12-month old) to 39.5 +/- 2.9 nmoles/microg/hr (30-month old). Following HU, LDH activity of single Type IIB fibers increased by 22% (52.0 +/- 3.4 to 66.4 +/- 3.2 nmoles/microg/hr) in the 12-month-old animals, whereas no difference was observed with HU in the Type IIB fibers of the 30-month-old animals. Following HU-Ex, LDH activity of Type IIB fibers in the 12-month-old animals was not significantly different from that of Type IIB fibers from HU animals, whereas a significant increase was observed (38.1 +/- 2.9 to 51.8 +/- 3.1 nmoles/microg/hr) in Type IIB fibers of 30-month-old animals, for HU and HU-Ex, respectively. Analysis of variance revealed an interaction between age and condition, indicating that Type IIB fibers from adult and aged animals have a different biochemical response to inactivity. The enzyme activities for BHAD were not different between the experimental conditions. The results demonstrate that the total LDH enzyme activities of the Type IIB fibers decrease with age, suggesting an age-related shift in the biochemical profile. Further, single skeletal muscle fiber adaptation is age-dependent.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2002

Force generation, but not myosin ATPase activity, declines with age in rat muscle fibers.

We tested the hypothesis that age-associated decline in muscle function is related to a change in myosin ATPase activity. Single, glycerinated semimembranosus fibers from young (8-12 mo) and aged (32-37 mo) Fischer 344 x Brown Norway male rats were analyzed simultaneously for force and myosin ATPase activity over a range of Ca2+ concentrations. Maximal force generation was ~20% lower in fibers from aged animals (P = 0.02), but myosin ATPase activity was not different between fibers from young and aged rats: 686 +/- 46 (n = 30) and 697 +/- 46 microM/s (n = 33) (P = 0.89). The apparent rate constant for the dissociation of strong-binding myosin from actin was calculated to be ~30% greater in fibers from aged animals (P = 0.03), indicating that the lower force produced by fibers from aged animals is due to a greater flux of myosin heads from the strong-binding state to the weak-binding state during contraction. This is in agreement with our previous electron paramagnetic resonance experiments that showed a reduced fraction of myosin heads in the strong-binding state during a maximal isometric contraction in fibers from older rats.

Adenosine Triphosphate↗

PubMed2002

Skeletal muscle adaptations with age, inactivity, and therapeutic exercise.

One of the remarkable features of skeletal muscle is its adaptability. Skeletal muscle adaptations are characterized by modifications of morphological, biochemical, and molecular variables that alter the functional attributes of specific skeletal muscle fiber types. Skeletal muscle adaptation is diverse and the magnitude of change is dependent on many factors, such as activity pattern, age, and muscle fiber type composition. The adaptation of skeletal muscle in the adult population is well described. In contrast, the adaptation of skeletal muscle in the older population is less documented, especially in the area of inactivity-induced alterations. Age-related changes in skeletal muscle may play a significant role in the magnitude of change with inactivity and influence the rehabilitation process for the older adult. A consistent feature of age and inactivity is limb muscle atrophy and the loss of peak force and power. Differences exist in the rate and mechanisms of muscle wasting and in the susceptibility of a given fiber type to atrophy. Most likely, the rapid muscle wasting might be in part due to a decrease in protein synthesis coupled with an increased degradation. Besides the quantitative change in muscle mass, age and inactivity induce important qualitative changes in the structure of key skeletal muscle proteins that are manifested in alterations in contractile properties. Therefore, the purpose of this clinical commentary is to identify the major effects of age and inactivity on skeletal muscle structure and function, and discuss potential therapeutic interventions. Special emphasis will be placed on how alterations in muscle structure affect function and on the cellular and molecular mechanisms of the age-related and inactivity-induced muscle changes.

Adaptation, Physiological↗