Effects of type 1 diabetes mellitus on skeletal muscle: clinical observations and physiological mechanisms

Diabetes pharmacotherapy and effects on the musculoskeletal system

Persons with type 1 or type 2 diabetes have a significantly higher fracture risk than age-matched persons without diabetes, attributed to disease-specific deficits in the microarchitecture and material properties of bone tissue. Therefore, independent effects of diabetes drugs on skeletal integrity are vitally important. Studies of incretin-based therapies have shown divergent effects of different agents on fracture risk, including detrimental, beneficial, and neutral effects. The sulfonylurea class of drugs, owing to its hypoglycemic potential, is thought to amplify the risk of fall-related fractures, particularly in the elderly. Other agents such as the biguanides may, in fact, be osteo-anabolic. In contrast, despite similarly expected anabolic properties of insulin, data suggests that insulin pharmacotherapy itself, particularly in type 2 diabetes, may be a risk factor for fracture, negatively associated with determinants of bone quality and bone strength. Finally, sodium-dependent glucose co-transporter 2 inhibitors have been associated with an increased risk of atypical fractures in select populations, and possibly with an increase in lower extremity amputation with specific SGLT2I drugs. The role of skeletal muscle, as a potential mediator and determinant of bone quality, is also a relevant area of exploration. Currently, data regarding the impact of glucose lowering medications on diabetes-related muscle atrophy is more limited, although preclinical studies suggest that various hypoglycemic agents may have either aggravating (sulfonylureas, glinides) or repairing (thiazolidinediones, biguanides, incretins) effects on skeletal muscle atrophy, thereby influencing bone quality. Hence, the therapeutic efficacy of each hypoglycemic agent must also be evaluated in light of its impact, alone or in combination, on musculoskeletal health, when determining an individualized treatment approach. Moreover, the effect of newer medications (potentially seeking expanded clinical indication into the pediatric age range) on the growing skeleton is largely unknown. Herein, we review the available literature regarding effects of diabetes pharmacotherapy, by drug class and/or by clinical indication, on the musculoskeletal health of persons with diabetes.

Protective effects of Liuwei dihuang water extracts on diabetic muscle atrophy

BACKGROUND

Liuwei dihuang (LWDH), a widely used traditional Chinese herbal medicine, has been noticed for its potential on the improvement of diabetic complications including diabetic nephropathy and diabetic encephalopathy. However, whether LWDH can improve the effects of diabetic skeletal muscle atrophy has not yet been reported.

PURPOSE

The present study aimed to investigate the protective effects and mechanisms of the water extract of Liuwei dihuang (LWDH-WE) on skeletal muscle in cellular and animal models of diabetic muscle atrophy.

STUDY DESIGN

The muscle protective effects of LWDH-WE on diabetic muscle atrophy and weakness were examined in methylglyoxal (MG)-treated C2C12 myotubes and streptozotocin (STZ)-treated C57BL/6 mice, respectively.

METHODS

C2C12 myoblasts were differentiated by differentiation medium to form myotube structures. C2C12 myotubes were pre-treated with LWDH-WE 1 h before MG treatment. Diabetic mice were induced by single intraperitoneal injection of STZ (150 mg/kg) in C57BL/6 mice. Cell viability was determined by MTT and LDH assays. Protein expressions were detected by western blots. Morphological changes of cells were observed by an inverted microscope. Mitochondria membrane potential and reactive oxygen species (ROS) production were measured by flow cytometry. Muscle strength was evaluated by measuring grip strength of mice.

RESULTS

In C2C12 myotubes, LWDH-WE attenuated MG-induced cellular death and oxidative damage accompanied with improving mitochondrial membrane potential, inhibiting NADPH oxidase (Nox) activation, and ROS production. Moreover, LWDH-WE could attenuate MG-induced atrophy of C2C12 myotubes accompanied with regulating protein synthesis (IGF-1R, Akt, mTOR) and protein degradation (FoxO3a, atrogin-1, MuRF-1) signals. In STZ-induced diabetic mice, LWDH-WE improved body weight and skeletal muscle mass of mice. LWDH-WE also enhanced muscle strength of STZ-induced diabetic mice. Furthermore, LWDH-WE enhanced the improvement of insulin on gastrocnemius muscle mass and grip strength in STZ-treated mice.

CONCLUSION

LWDH-WE possesses skeletal muscle protection via reducing oxidative damage and regulating protein synthesis and degradation pathways in MG-induced atrophy of C2C12 myotubes. We also reveal the novel protection of LWDH-WE against STZ-induced reduction of muscle mass and muscle strength in mice.

Resistance Isn't Futile: The Physiological Basis of the Health Effects of Resistance Exercise in Individuals With Type 1 Diabetes

The importance of regular exercise for glucose management in individuals with type 1 diabetes is magnified by its acknowledgment as a key adjunct to insulin therapy by several governmental, charitable, and healthcare organisations. However, although actively encouraged, exercise participation rates remain low, with glycaemic disturbances and poor cardiorespiratory fitness cited as barriers to long-term involvement. These fears are perhaps exacerbated by uncertainty in how different forms of exercise can considerably alter several acute and chronic physiological outcomes in those with type 1 diabetes. Thus, understanding the bodily responses to specific forms of exercise is important for the provision of practical guidelines that aim to overcome these exercise barriers. Currently, the majority of existing exercise research in type 1 diabetes has focused on moderate intensity continuous protocols with less work exploring predominately non-oxidative exercise modalities like resistance exercise. This is surprising, considering the known neuro-muscular, osteopathic, metabolic, and vascular benefits associated with resistance exercise in the wider population. Considering that individuals with type 1 diabetes have an elevated susceptibility for complications within these physiological systems, the wider health benefits associated with resistance exercise may help alleviate the prevalence and/or magnitude of pathological manifestation in this population group. This review outlines the health benefits of resistance exercise with reference to evidence in aiding some of the common complications associated with individuals with type 1 diabetes.

Juzentaihoto hot water extract alleviates muscle atrophy and improves motor function in streptozotocin-induced diabetic oxidative stress mice

A decrease in skeletal muscle mass and motor function occurs in diabetic patients. In type 1 diabetic patients, in particular, fast-type fiber-dominated muscle atrophy occurs due to increased oxidative stress and inflammation. Juzentaihoto is a herbal medicine that has been found to be effective in reducing oxidative stress. In this study, juzentaihoto hot water extract (JTT) was administered prophylactically to mice with diabetic oxidative stress, which was induced by an injection of streptozotocin, and the effects on skeletal muscle mass, motor function, and antioxidant activity were evaluated. In mice that were administered JTT, skeletal muscle atrophy and loss of motor function were suppressed. Additionally, the administration of JTT increased the mRNA expression level of Sirt1 and the activity of superoxide dismutase in the gastrocnemius. In addition to skeletal muscle atrophy, atrophy of the liver, spleen and thymus gland, and kidney hypertrophy were also suppressed. Furthermore, in order to evaluate the antioxidant activity of 10 constituent crude drugs that comprise juzentaihoto, Sirt1 transcriptional activity in C2C12 cells was evaluated. The Sirt1 transcriptional activity was increased by Cinnamomi Cortex, Astragali Radix, and Glycyrrhizae Radix extracts. These three constituent crude drugs play an important function in the antioxidant action of juzentaihoto, suggesting that juzentaihoto can prevent muscle atrophy by decreasing oxidative stress.

Brain-derived neurotrophic factor, insulin like growth factor-1 and inflammatory cytokine responses to continuous and intermittent exercise in patients with type 1 diabetes

AIMS

Type 1 diabetes mellitus (T1DM) is an important risk factor for cognitive decline and motor dysfunction due to progressive muscular atrophy. Chronic hyperglycemia may be responsible for impaired vascular function, loss of muscle mass, and morphological abnormalities in the myocytes. For the proper functioning of the neuromuscular system, two crucial growth factors are necessary: brain-derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1), whose reduced expressions have been implicated in progressive neuropathy and muscle atrophy in patients with T1DM. The aim of the study was to compare the effects of two different exercise regimes (continuous and intermittent) on BDNF, IGF-1, blood glucose and inflammatory cytokine responses in young adults with and without Type 1 diabetes.

METHODS

Fourteen patients (aged: 26.9 years) with T1DM and age-matched adults without diabetes participated in a 40 min continuous exercise (ExC, 50% of lactate threshold) and a high intensity intermittent exercise (ExInt, 120% of lactate threshold). During the study the patients performed self-monitoring of blood glucose levels (SMBG) under glycemic control. The effects of ExC and ExInt on BDNF, IGF-1, insulin like growth factor binding protein (IGFBP-3), insulin (INS), vascular endothelial growth factor (VEGF), transforming growth factor beta (TGF-β) and tumor necrosis factor alpha (TNF-α) were analyzed.

RESULTS

BDNF and IGF-1 baseline serum levels were significantly lower in the T1DM patients compared to the healthy controls, but we found that ExInt and ExC significantly increase the secretion of BDNF and IGF-1 levels. Significant increases in BDNF and TGF-β levels, higher blood glucose decline, and a lower incidence of hypoglycaemia in ExInt compared to ExC were observed. Lower IGFBP-3 concentrations were revealed in T1DM patients in response to ExInt compared to ExC, suggesting a positive effect on IGF-1/IGFBP-3 ratio and the bioavailability of IGF-1.

CONCLUSIONS

According to our results physical exercise has beneficial effects on serum BDNF and IGF-1 levels. A high-intensity intermittent exercise may be more effective at reducing the risk of exercise-induced glycaemic disorders in the T1DM patients as compared to continuous exercise.

Obesity in Type 1 Diabetes: Pathophysiology, Clinical Impact, and Mechanisms

There has been an alarming increase in the prevalence of obesity in people with type 1 diabetes in recent years. Although obesity has long been recognized as a major risk factor for the development of type 2 diabetes and a catalyst for complications, much less is known about the role of obesity in the initiation and pathogenesis of type 1 diabetes. Emerging evidence suggests that obesity contributes to insulin resistance, dyslipidemia, and cardiometabolic complications in type 1 diabetes. Unique therapeutic strategies may be required to address these comorbidities within the context of intensive insulin therapy, which promotes weight gain. There is an urgent need for clinical guidelines for the prevention and management of obesity in type 1 diabetes. The development of these recommendations will require a transdisciplinary research strategy addressing metabolism, molecular mechanisms, lifestyle, neuropsychology, and novel therapeutics. In this review, the prevalence, clinical impact, energy balance physiology, and potential mechanisms of obesity in type 1 diabetes are described, with a special focus on the substantial gaps in knowledge in this field. Our goal is to provide a framework for the evidence base needed to develop type 1 diabetes-specific weight management recommendations that account for the competing outcomes of glycemic control and weight management.

Metallothionein expression in slow- vs. fast-twitch muscle fibers following 4 weeks of streptozotocin-induced type 1 diabetes

Type 1 diabetes (T1DM) is known to cause an increase in reactive oxygen species (ROS) and elevated intracellular glucose levels. We investigated the metallothionein I and II (MT I+II) antioxidants expression in soleus (mainly slow-twitch) and plantaris (predominantly fast-twitch) skeletal muscle using a rodent model of streptozotocin-induced diabetes. The presence of oxidative stress was confirmed by the detection of increased levels of protein carbonyl formation in the diabetic tissues. DAB (3,3′-diaminobenzidine) immunostaining and Western blotting analyses demonstrated that MT I+II expression was significantly upregulated in the diabetic soleus and plantaris muscle tissues compared with their respective controls. Moreover, no significant difference was detected between the plantaris and soleus controls or between the plantaris and soleus diabetic tissues. These findings suggest that there is an increase in MT protein expression in the soleus and plantaris muscles associated with the induction of T1DM. A better understanding of the molecular mechanisms that allow MT to prevent the oxidative stress associated with diabetes could lead to a novel therapeutic strategy for this chronic disease and its associated complications.

Diabetic Myopathy: current molecular understanding of this novel neuromuscular disorder

PURPOSE OF REVIEW

Here we summarize the evidence from human studies of the impairments to the structural, functional, and metabolic capacities in skeletal muscle in those with type 1 diabetes (T1D) - a condition known as diabetic myopathy. Given the importance of skeletal muscle for blood lipid and glucose management, the development and progression of diabetic myopathy would not only lead to increased insulin resistance, but also impact the ability to mitigate dysglycemic/dyslipidemic burdens.

RECENT FINDINGS

Despite the importance of skeletal muscle in whole-body metabolic control, studies investigating diabetic myopathy are startling limited. Recent findings have demonstrated that those with T1D exhibit decreased force production, increased fatigability, loss of muscle stem cells, and a greater reliance on glycolytic metabolism, as a result of reduced mitochondrial capacity.

SUMMARY

We propose a mechanistic model for the development of diabetic myopathy based on the human findings to date. This model suggests that repeated insulin injections in those with T1D leads to recurrent periods of intracellular hyperglycemia in myofibers. Resultant reductions in mitochondrial function lead to greater reliance on glycolytic metabolism and a concomitant shift in fiber type composition. Studies defining the scope and magnitude of diabetic myopathy and testing the veracity of this model are urgently needed in order to develop appropriate therapeutic strategies to maximize muscle health in those with T1D.

Differences in muscle metabolism in patients with type I diabetes - influence of gender and nephropathy studied by (31)P MR spectroscopy

Type I diabetes mellitus (DM1) is a complex disease with adverse effects on organs and tissues despite compensation by insulin treatment. The goal of our study was to study how kidney diseases change (31)P MR parameters of muscle metabolism in DM1 patients with respect to gender. 51 DM1 patients (19 m/14 f without and 13 m/5 f with nephropathy) and 26 (14 m/12 f) healthy volunteers were examined using (31)P magnetic resonance spectroscopy at 3T tomograph at rest, and during and after a calf muscle exercise. The exercise consisted of a six-minute plantar flexion using a pedal ergometer followed by a six-minute recovery. It is reflected by reduced relative beta-ATP and increased Pi and phosphodiester signals to phosphocreatine (PCr) at rest and prolongation of the PCr recovery time after the exercise. Measurement on healthy volunteers indicated differences between males and females in pH at the rest and after the exercise only. These differences between patients groups were not significant. We have proven that nephropathy affects the metabolism in diabetic patients and our results confirm significant difference between patients with and without nephropathy. Gender differences in pH were observed only between male and female healthy volunteers.

Comparison of Hand Function Between Children With Type 1 Diabetes Mellitus and Children Without Type 1 Diabetes Mellitus

PURPOSE

This study compared the hand function of children between the ages of 8 and 12 years with type 1 diabetes mellitus (T1DM) with that of children without diabetes.

METHODS

The Modified Jebsen-Taylor Hand Function Test and the Purdue Pegboard Test were used to assess hand function. The Pediatric Quality of Life Inventory 4.0 was used for evaluating health-related quality of life.

RESULTS

Duration of writing was found to be significantly longer on the dominant side of the T1DM group compared with the children without T1DM. The durations of card turning, moving large, light objects, and large, heavy objects on the nondominant side of the T1DM group were also found to be significantly longer than those in the children without T1DM. The total scale score of health-related quality of life was significantly lower in the T1DM group compared with the children without T1DM.

CONCLUSIONS

T1DM affects hand function, particularly the dominant side for writing and nondominant side for card turning and moving large objects.

Low-intensity pulsed ultrasound prevents muscle atrophy induced by type 1 diabetes in rats

Background

Type 1 diabetes mellitus (T1DM) induces serious skeletal muscle atrophy. Low-intensity pulsed ultrasound (LIPUS) is a common treatment for skeletal muscle injury and is effective in accelerating the rate of muscle growth. However, to the best of our knowledge, whether LIPUS can improve skeletal muscle atrophy in type 1 diabetic rats has not been investigated.

Methods

The rats were randomly divided into four groups: the normal control group (NC); the sham-treated diabetic control group (DC); the diabetic, insulin-treated group (DI) as a positive control; and the diabetic LIPUS therapy group (DL). The DL rats were treated with LIPUS (1 MHz, 30 mW/cm²) on the gastrocnemius for 20 min/day.

Results

After 6 weeks, the rats in the DC group showed severe muscle atrophy. However, LIPUS significantly improved type 1 diabetes-induced muscle atrophy, as evidenced by significantly enhanced muscle cross-sectional area, muscle mass, and strength. Moreover, compared with the DC group, LIPUS significantly activated Akt and upregulated the expression of mTOR, and LIPUS downregulated the expression of MSTN, its receptor ActRIIB, and FoxO1.

Conclusions

These results indicate that LIPUS improved muscle atrophy induced by type 1 diabetes, and the MSTN/Akt/mTOR&FoxO1 signaling pathway may play a role in this improvement.

Statin Therapy Negatively Impacts Skeletal Muscle Regeneration and Cutaneous Wound Repair in Type 1 Diabetic Mice

Those with diabetes invariably develop complications including cardiovascular disease (CVD). To reduce their CVD risk, diabetics are generally prescribed cholesterol-lowering 3-hydroxy-methylglutaryl coenzyme A reductase inhibitors (i.e., statins). Statins inhibit cholesterol biosynthesis, but also reduce the synthesis of a number of mevalonate pathway intermediates, leading to several cholesterol-independent effects. One of the pleiotropic effects of statins is the reduction of the anti-fibrinolytic hormone plasminogen activator inhibitor-1 (PAI-1). We have previously demonstrated that a PAI-1 specific inhibitor alleviated diabetes-induced delays in skin and muscle repair. Here we tested if statin administration, through its pleiotropic effects on PAI-1, could improve skin and muscle repair in a diabetic rodent model. Six weeks after diabetes onset, adult male streptozotocin-induced diabetic (STZ), and WT mice were assigned to receive control chow or a diet enriched with 600 mg/kg Fluvastatin. Tibialis anterior muscles were injured via Cardiotoxin injection to induce skeletal muscle injury. Punch biopsies were administered on the dorsal scapular region to induce injury of skin. Twenty-four days after the onset of statin therapy (10 days post-injury), tissues were harvested and analyzed. PAI-1 levels were attenuated in statin-treated diabetic tissue when compared to control-treated tissue, however no differences were observed in non-diabetic tissue as a result of treatment. Muscle and skin repair were significantly attenuated in Fluvastatin-treated STZ-diabetic mice as demonstrated by larger wound areas, less mature granulation tissue, and an increased presence of smaller regenerating muscle fibers. Despite attenuating PAI-1 levels in diabetic tissue, Fluvastatin treatment impaired cutaneous healing and skeletal muscle repair in STZ-diabetic mice.

Muscle force distribution of the lower limbs during walking in diabetic individuals with and without polyneuropathy

BACKGROUND

Muscle force estimation could advance the comprehension of the neuromuscular strategies that diabetic patients adopt to preserve walking ability, which guarantees their independence as they deal with their neural and muscular impairments due to diabetes and neuropathy. In this study, the lower limb's muscle force distribution during gait was estimated and compared in diabetic patients with and without polyneuropathy.

METHODS

Thirty individuals were evaluated in a cross-sectional study, equally divided among controls (CG) and diabetic patients with (DNG) and without (DG) polyneuropathy. The acquired ground reaction forces and kinematic data were used as input variables for a scaled musculoskeletal model in the OpenSim software. The maximum isometric force of the ankle extensors and flexors was reduced in the model of DNG by 30% and 20%, respectively. The muscle force was calculated using static optimization, and peak forces were compared among groups (flexors and extensors of hip, knee, and ankle; ankle evertors; and hip abductors) using MANOVAs, followed by univariate ANOVAs and Newman-Keuls post-hoc tests (p < 0.05).

RESULTS

From the middle to late stance phase, DG showed a lower soleus muscle peak force compared to the CG (p=0.024) and the DNG showed lower forces in the gastrocnemius medialis compared to the DG (p=0.037). At the terminal swing phase, the semitendinosus and semimembranosus peak forces showed lower values in the DG compared to the CG and DNG. At the late stance, the DNG showed a higher peak force in the biceps short head, semimembranosus, and semitendinosus compared to the CG and DG.

CONCLUSION

Peak forces of ankle (flexors, extensors, and evertors), knee (flexors and extensors), and hip abductors distinguished DNG from DG, and both of those from CG. Both diabetic groups showed alterations in the force production of the ankle extensors with reductions in the forces of soleus (DG) and gastrocnemius medialis (DNG) seen in both diabetic groups, but only DNG showed an increase in the hamstrings (knee flexor) at push-off. A therapeutic approach focused on preserving the functionality of the knee muscles is a promising strategy, even if the ankle dorsiflexors and plantarflexors are included in the resistance training.

Hypertrophy Stimulation at the Onset of Type I Diabetes Maintains the Soleus but Not the EDL Muscle Mass in Wistar Rats

Diabetes mellitus induces a reduction in skeletal muscle mass and strength. Strength training is prescribed as part of treatment since it improves glycemic control and promotes increase of skeletal muscle mass. The mechanisms involved in overload-induced muscle hypertrophy elicited at the establishment of the type I diabetic state was investigated in Wistar rats. The purpose was to examine whether the overload-induced hypertrophy can counteract the hypotrophy associated to the diabetic state. The experiments were performed in oxidative (soleus) or glycolytic (EDL) muscles. PI3K/Akt/mTOR protein synthesis pathway was evaluated 7 days after overload-induced hypertrophy of soleus and of EDL muscles. The mRNA expression of genes associated with different signaling pathways that control muscle hypertrophy was also evaluated: mechanotransduction (FAK), Wnt/β-catenin, myostatin, and follistatin. The soleus and EDL muscles when submitted to overload had similar hypertrophic responses in control and diabetic animals. The increase of absolute and specific twitch and tetanic forces had the same magnitude as muscle hypertrophic response. Hypertrophy of the EDL muscle from diabetic animals mostly involved mechanical loading-stimulated PI3K/Akt/mTOR pathway besides the reduced activation of AMP-activated protein kinase (AMPK) and decrease of myostatin expression. Hypertrophy was more pronounced in the soleus muscle of diabetic animals due to a more potent activation of rpS6 and increased mRNA expression of insulin-like growth factor-1 (IGF-1), mechano-growth factor (MGF) and follistatin, and decrease of myostatin, MuRF-1 and atrogin-1 contents. The signaling changes enabled the soleus muscle mass and force of the diabetic rats to reach the values of the control group.

Why should people with type 1 diabetes exercise regularly?

Plethoric evidence reminds of the protective effects of exercise against a number of health risks, across all ages, in the general population. The benefits of exercise for individuals with type 2 diabetes are indisputable. An in-depth understanding of energy metabolism has reasonably entailed exercise as a cornerstone in the lifestyle of almost all subjects with type 1 diabetes. Nevertheless, individuals with type 1 diabetes often fail in accomplishing exercise guidelines and they are less active than their peer without diabetes. Two major obstacles are feared by people with type 1 diabetes who wish to exercise regularly: management of blood glucose control and hypoglycemia. Nowadays, strategies, including glucose monitoring technology and insulin pump therapy, have significantly contributed to the participation in regular physical activity, and even in competitive sports, for people with type 1 diabetes. Novel modalities of training, like different intensity, interspersed exercise, are as well promising. The beneficial potential of exercise in type 1 diabetes is multi-faceted, and it has to be fully exploited because it goes beyond the insulin-mimetic action, possibly through immunomodulation.

The impact of type 1 diabetes and diabetic polyneuropathy on muscle strength and fatigability

AIMS

Although it is widely accepted that diabetic polyneuropathy (DPN) is linked to a marked decline in neuromuscular performance, information on the possible impact of type 1 diabetes (T1D) on muscle strength and fatigue remains unclear. The purpose of this study was to investigate the effects of T1D and DPN on strength and fatigability in knee extensor muscles.

METHODS

Thirty-one T1D patients (T1D), 22 T1D patients with DPN (DPN) and 23 matched healthy control participants (C) were enrolled. Maximal voluntary contraction (MVC) and endurance time at an intensity level of 50% of the MVC were assessed at the knee extensor muscles with an isometric dynamometer. Clinical characteristics of diabetic patients were assessed by considering a wide range of vascular and neurological parameters.

RESULTS

DPN group had lower knee extensor muscles strength than T1D (-19%) and the C group (-37.5%). T1D group was 22% weaker when compared to the C group. Lower body muscle fatigability of DPN group was 22 and 45.5% higher than T1D and C group, respectively. T1D group possessed a higher fatigability (29.4%) compared to C group. A correlation was found between motor and sensory nerve conduction velocity and muscle strength and fatigability.

CONCLUSIONS

Patients with T1D are characterised by both a higher fatigability and a lower muscle strength, which are aggravated by DPN. Our data suggest that factors other than nervous damage play a role in the pathogenesis of such defect.

Poor glycaemic control is associated with reduced exercise performance and oxygen economy during cardio-pulmonary exercise testing in people with type 1 diabetes

BACKGROUND

To explore the impact of glycaemic control (HbA_1c) on functional capacity during cardio-pulmonary exercise testing in people with type 1 diabetes.

METHODS

Sixty-four individuals with type 1 diabetes (age: 34 ± 8 years; 13 females, HbA_1c: 7.8 ± 1% (62 ± 13 mmol/mol), duration of diabetes: 17 ± 9 years) performed a cardio-pulmonary cycle ergometer exercise test until volitional exhaustion. Stepwise linear regression was used to explore relationships between HbA_1c and cardio-respiratory data with p ≤ 0.05. Furthermore, participants were divided into quartiles based on HbA_1c levels and cardio-respiratory data were analysed by one-way ANOVA. Multiple regression analysis was performed to explore the relationships between changes in time to exhaustion and cardio-respiratory data. Data were adjusted for confounder.

RESULTS

HbA_1c was related to time to exhaustion and oxygen consumption at the power output elicited at the sub-maximal threshold of the heart rate turn point (r = 0.47, R² = 0.22, p = 0.03). Significant differences were found at time to exhaustion between QI vs. QIV and at oxygen consumption at the power output elicited at the heart rate turn point between QI vs. QII and QI vs. QIV (p < 0.05). Changes in oxygen uptake, power output and in oxygen consumption at the power output elicited at the heart rate turn point and at maximum power output explained 55% of the variance in time to exhaustion (r = 0.74, R² = 0.55, p < 0.01).

CONCLUSIONS

Poor glycaemic control is related to less economical use of oxygen at sub-maximal work rates and an earlier time to exhaustion during cardio-pulmonary exercise testing. However, exercise training could have the same potential to counteract the influence of poor glycaemic control on functional capacity. Trial registration NCT01704417. Date of registration: October 11, 2012.

Changes in the Diaphragm Lipid Content after Administration of Streptozotocin and High-Fat Diet Regime

The diaphragm is a dome-shaped skeletal muscle indispensable for breathing. Its activity contributes up to 70% of the total ventilatory function at rest. In comparison to other skeletal muscles, it is distinguished by an oxidative phenotype and uninterrupted cyclic contraction pattern. Surprisingly, the research regarding diaphragm diabetic phenotype particularly in the light of lipid-induced insulin resistance is virtually nonexistent. Male Wistar rats were randomly allocated into 3 groups: control, streptozotocin-induced (STZ) type-1 diabetes, and rodents fed with high-fat diet (HFD). Additionally, half of the animals from each group were administered with myriocin, a robust, selective inhibitor of ceramide synthesis and, therefore, a potent agent ameliorating insulin resistance. Diaphragm lipid contents were evaluated using chromatography. Fatty acid transporter expression was determined by Western blot. The STZ and HFD rats had increased concentration of lipids, namely, ceramides (CER) and diacylglycerols (DAG). Interestingly, this coincided with an increased concentration of long-chain (C ≥ 16) saturated fatty acid species present in both the aforementioned lipid fractions. The CER/DAG accumulation was accompanied by an elevated fatty acid transporter expression (FATP-1 in HFD and FATP-4 in STZ). Surprisingly, we observed a significantly decreased triacylglycerol content in the diaphragms of STZ-treated rats.

Decreased Satellite Cell Number and Function in Humans and Mice With Type 1 Diabetes Is the Result of Altered Notch Signaling

Type 1 diabetes (T1D) negatively influences skeletal muscle health; however, its effect on muscle satellite cells (SCs) remains largely unknown. SCs from samples from rodents (Akita) and human subjects with T1D were examined to discern differences in SC density and functionality compared with samples from their respective control subjects. Examination of the Notch pathway was undertaken to investigate its role in changes to SC functionality. Compared with controls, Akita mice demonstrated increased muscle damage after eccentric exercise along with a decline in SC density and myogenic capacity. Quantification of components of the Notch signaling pathway revealed a persistent activation of Notch signaling in Akita SCs, which could be reversed with the Notch inhibitor DAPT. Similar to Akita samples, skeletal muscle from human subjects with T1D displayed a significant reduction in SC content, and the Notch ligand, DLL1, was significantly increased compared with control subjects, supporting the dysregulated Notch pathway observed in Akita muscles. These data indicate that persistent activation in Notch signaling impairs SC functionality in the T1D muscle, resulting in a decline in SC content. Given the vital role played by the SC in muscle growth and maintenance, these findings suggest that impairments in SC capacities play a primary role in the skeletal muscle myopathy that characterizes T1D.

Active Subjects With Autoimmune Type 1 Diabetes Have Better Metabolic Profiles Than Sedentary Controls

Previous studies in humans with type 1 diabetes mellitus (T1D) and in nonobese diabetic mice have investigated the beneficial immunomodulatory potential of aerobic physical activity. Performing high volume of aerobic exercise may favorably regulate autoimmunity in diabetes. We tested whether increased physical activity is a self-sufficient positive factor in T1D subjects. During a 3-month observational period, active (six males; 40.5 ± 6.1 years; BMI: 24.5 ± 2.1) and sedentary (four males, three females; 35.9 ± 8.9 years; BMI: 25.7 ± 3.8) T1D individuals on insulin pump therapy were studied for metabolic, inflammatory, and autoimmune parameters. At baseline and at the end of a 3-month period, glycosylated hemoglobin (HbA1c), autoantibodies (anti-GAD, anti-ZnT8, anti-IA2, and ICA) and proinflammatory cytokines (IL-6 and TNF-α) were evaluated. During the third month of the period, physically active T1D patients showed a significant reduction in the average glucose levels (-9%, p = 0.025, by CGM) compared to the first month values, and even their hyperglycemic episodes (>180 mg/dl) diminished significantly (-24.2%, p = 0.032 vs. first month). Moreover, active T1D subjects exhibited an improved body composition with respect to sedentary controls. No significant changes were detected as to the autoimmune and inflammatory profiles. This study confirms the beneficial role of physical exercise associated with insulin pump therapy in order to improve metabolic control in individuals with T1D. These preliminary positive observations need to be challenged in a prolonged interventional follow-up.

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.

Muscle fiber conduction velocity in different gait phases of early and late-stage diabetic neuropathy

We investigated the muscle fiber conduction velocity (MFCV) during gait phases of the lower limb muscles in individuals with various degrees of diabetic peripheral neuropathy (DPN). Forty-five patients were classified into severity degrees of DPN by a fuzzy model. The stages were absent (n=11), mild (n=14), moderate (n=11) and severe (n=9), with 10 matched healthy controls. While walking, all subjects had their sEMG (4 linear electrode arrays) recorded for tibialis anterior (TA), gastrocnemius medialis (GM), vastus lateralis (VL) and biceps femoris (BF). MFCV was calculated using a maximum likelihood algorithm with 30ms standard deviation Gaussian windows. In general, individuals in the earlier stages of DPN showed lower MFCV of TA, GM and BF, whilst individuals with severe DPN presented higher MFCV of the same muscles. We observed that mild patients already showed lower MFCV of TA at early stance and swing, and lower MFCV of BF at swing. All diabetic groups showed a markedly reduction in MFCV of VL, irrespective of DPN. Severe patients presented higher MFCV mainly in distal muscles, TA at early and swing phases and GM at propulsion and midstance. The absent group already showed MFCV of VL and GM reductions at the propulsion phase and of VL at early stance. Although MFCV changes were not as progressive as the DPN was, we clearly distinguished diabetic patients from controls, and severe patients from all others.

Vitamin D deficiency aggravates diabetes-induced muscle wasting in female mice

We recently reported that vitamin D deficiency aggravates diabetic bone loss in mice. Although vitamin D affects both muscle and bone, the role of the vitamin D state in diabetic muscle loss and muscle-bone relationships remains unclear. In the present study, we examined the effects of vitamin D deficiency on muscle mass, muscle differentiation and muscle-derived humoral factors linking muscle to bone in diabetic female mice. Diabetes was induced in mice by streptozotocin (STZ) injection after feeding with a normal or vitamin D-deficient diet for 6 weeks. Quantitative computed tomography analysis showed that tibial muscle mass was significantly decreased in diabetic mice compared with control mice 4 weeks after induction of diabetes. Vitamin D deficiency accelerated muscle loss in diabetic mice. Vitamin D deficiency augmented the decreases in Pax7 mRNA levels and the increases in muscle RING-Finger Protein-1 and atrogin-1 mRNA levels induced by diabetes in the gastrocnemius muscle of mice. Moreover, vitamin D deficiency decreased the mRNA levels of insulin-like growth factor-1, fibroblast growth factor-2 and osteoglycin in muscle of diabetic mice. In conclusion, we demonstrated that vitamin D deficiency aggravates muscle loss induced by diabetes in female mice. Vitamin D may exert significant effects on the maintenance of the musculoskeletal system partly through the muscle-bone relationships in diabetic state.

Cathelicidin suppresses lipid accumulation and hepatic steatosis by inhibition of the CD36 receptor

BACKGROUND AND OBJECTIVES

Obesity is a global epidemic which increases the risk of the metabolic syndrome. Cathelicidin (LL-37 and mCRAMP) is an antimicrobial peptide with an unknown role in obesity. We hypothesize that cathelicidin expression correlates with obesity and modulates fat mass and hepatic steatosis.

MATERIALS AND METHODS

Male C57BL/6 J mice were fed a high-fat diet. Streptozotocin was injected into mice to induce diabetes. Experimental groups were injected with cathelicidin and CD36 overexpressing lentiviruses. Human mesenteric fat adipocytes, mouse 3T3-L1 differentiated adipocytes and human HepG2 hepatocytes were used in the in vitro experiments. Cathelicidin levels in non-diabetic, prediabetic and type II diabetic patients were measured by enzyme-linked immunosorbent assay.

RESULTS

Lentiviral cathelicidin overexpression reduced hepatic steatosis and decreased the fat mass of high-fat diet-treated diabetic mice. Cathelicidin overexpression reduced mesenteric fat and hepatic fatty acid translocase (CD36) expression that was reversed by lentiviral CD36 overexpression. Exposure of adipocytes and hepatocytes to cathelicidin significantly inhibited CD36 expression and reduced lipid accumulation. Serum cathelicidin protein levels were significantly increased in non-diabetic and prediabetic patients with obesity, compared with non-diabetic patients with normal body mass index (BMI) values. Prediabetic patients had lower serum cathelicidin protein levels than non-diabetic subjects.

CONCLUSIONS

Cathelicidin inhibits the CD36 fat receptor and lipid accumulation in adipocytes and hepatocytes, leading to a reduction of fat mass and hepatic steatosis in vivo. Circulating cathelicidin levels are associated with increased BMI. Our results demonstrate that cathelicidin modulates the development of obesity.

Insulin-driven translational capacity is impaired in primary fibroblasts of Prader Willi

Prader-Willi (PW) syndrome is a rare genetic disorder characterized by hypothalamic-pituitary abnormalities and severe hypotonia, hyperphagia, behavioural and psychiatric problems. Absence of satiety leads to severe obesity and frequently to diabetes. Furthermore, adult patients suffer from a severe loss of muscle mass, which severely impacts their quality of life. The mechanisms underlying alterations in muscle growth in PW remain to be clarified. In this study we explored the hypothesis that, in PW cells, alterations of protein synthesis are determined by dysfunctions in the promotion of cell growth. In order to study the molecular changes leading to dysfunction in protein translation, primary fibroblasts derived from four PW patients and five control subjects were used to study the insulin-mediated signaling pathway implicated in the control of protein synthesis by immunoblotting. Here we present, for the first time, evidences that the protein translation response to insulin is impaired in PW fibroblasts. Insulin alone has a major upregulatory effect on protein kinase B (AKT), glycogen synthase kinase (GSK3beta), while phosphorylation of p70S6K1 protein elongation factor controlled by mammalian target of rapamycin complex I (mTORC1) is reduced. In addition, we provide data that the response to insulin in PW cells can be restored by previous treatment with the amino acid L-Leucine (L-Leu). Our experiments in primary cell cultures demonstrate an impairment of insulin signaling that can be rescued by supplementation with the branched aminoacid L-Leu, indicating a possible therapeutic approach for alleviating muscle mass loss in PW patients.

Single muscle fiber contractile properties in diabetic RAT muscle

INTRODUCTION

Diabetes is associated with accelerated loss of muscle mass and function. We compared the contractile properties of single muscle fibers in young rat soleus muscle of uncontrolled streptozotocin-induced diabetic animals (n = 10) and nondiabetic controls (n = 10).

METHODS

Single fiber maximal force, shortening velocity, and power were assessed during maximal activation with calcium using the slack test 4 weeks after induction. Myosin heavy chain expression was determined using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Oxidized myosin levels were detected by analyzing protein carbonyls in muscle homogenates. All fibers expressed the type I myosin heavy chain isoform.

RESULTS

Diabetic rats had higher blood glucose (537 vs. 175 mg/dl; P < 0.001) and lower body weight (171 vs. 356 g; P < 0.001) than controls. Muscle fibers from diabetic rats showed smaller cross-sectional area (1128 vs. 1812 μm(2) ), lower maximal force (258 vs. 492 μN), and reduced absolute power (182 vs. 388 μN FL/s) (all P < 0.0001). No differences were seen in shortening velocity, specific force or specific power. Myosin carbonylation was higher (P < 0.01) in diabetic rats.

CONCLUSIONS

After 4 weeks of untreated diabetes, there are significant alterations in muscle at the level of isolated single fibers and myosin protein, although some contractile properties seem to be protected. Muscle Nerve, 2015 Muscle Nerve 53: 958-964, 2016.

Statin Therapy Alters Lipid Storage in Diabetic Skeletal Muscle

While statins significantly reduce cholesterol levels and thereby reduce the risk of cardiovascular disease, the development of myopathy with statin use is a significant clinical side effect. Recent guidelines recommend increasing inclusion criteria for statin treatment in diabetic individuals; however, the impact of statins on skeletal muscle health in those with diabetes (who already suffer from impairments in muscle health) is ill defined. Here, we investigate the effects of fluvastatin treatment on muscle health in wild type (WT) and streptozotocin (STZ)-induced diabetic mice. WT and STZ-diabetic mice received diet enriched with 600 mg/kg fluvastatin or control chow for 24 days. Muscle morphology, intra and extracellular lipid levels, and lipid transporter content were investigated. Our findings indicate that short-term fluvastatin administration induced a myopathy that was not exacerbated by the presence of STZ-induced diabetes. Fluvastatin significantly increased ectopic lipid deposition within the muscle of STZ-diabetic animals, findings that were not seen with diabetes or statin treatment alone. Consistent with this observation, only fluvastatin-treated diabetic mice downregulated protein expression of lipid transporters FAT/CD36 and FABPpm in their skeletal muscle. No differences in FAT/CD36 or FABPpm mRNA content were observed. Altered lipid compartmentalization resultant of a downregulation in lipid transporter content in STZ-induced diabetic skeletal muscle was apparent in the current investigation. Given the association between ectopic lipid deposition in skeletal muscle and the development of insulin-resistance, our findings highlight the necessity for more thorough investigations into the impact of statins in humans with diabetes.

Advanced glycation end-products induce skeletal muscle atrophy and dysfunction in diabetic mice via a RAGE-mediated, AMPK-down-regulated, Akt pathway

Diabetic myopathy, a less studied complication of diabetes, exhibits the clinical observations characterized by a less muscle mass, muscle weakness and a reduced physical functional capacity. Accumulation of advanced glycation end-products (AGEs), known to play a role in diabetic complications, has been identified in ageing human skeletal muscles. However, the role of AGEs in diabetic myopathy remains unclear. Here, we investigated the effects of AGEs on myogenic differentiation and muscle atrophy in vivo and in vitro. We also evaluated the therapeutic potential of alagebrium chloride (Ala-Cl), an inhibitor of AGEs. Muscle fibre atrophy and immunoreactivity for AGEs, Atrogin-1 (a muscle atrophy marker) and phosphorylated AMP-activated protein kinase (AMPK) expressions were markedly increased in human skeletal muscles from patients with diabetes as compared with control subjects. Moreover, in diabetic mice we found increased blood AGEs, less muscle mass, lower muscular endurance, atrophic muscle size and poor regenerative capacity, and increased levels of muscle AGE and receptor for AGE (RAGE), Atrogin-1 and phosphorylated AMPK, which could be significantly ameliorated by Ala-Cl. Furthermore, in vitro, AGEs (in a dose-dependent manner) reduced myotube diameters (myotube atrophy) and induced Atrogin-1 protein expression in myotubes differentiated from both mouse myoblasts and primary human skeletal muscle-derived progenitor cells. AGEs exerted a negative regulation of myogenesis of mouse and human myoblasts. Ala-Cl significantly inhibited the effects of AGEs on myotube atrophy and myogenesis. We further demonstrated that AGEs induced muscle atrophy/myogenesis impairment via a RAGE-mediated AMPK-down-regulation of the Akt signalling pathway. Our findings support that AGEs play an important role in diabetic myopathy, and that an inhibitor of AGEs may offer a therapeutic strategy for managing the dysfunction of muscle due to diabetes or ageing.

Skeletal muscle as a therapeutic target for delaying type 1 diabetic complications

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease targeting the pancreatic beta-cells and rendering the person hypoinsulinemic and hyperglycemic. Despite exogenous insulin therapy, individuals with T1DM will invariably develop long-term complications such as blindness, kidney failure and cardiovascular disease. Though often overlooked, skeletal muscle is also adversely affected in T1DM, with both physical and metabolic derangements reported. As the largest metabolic organ in the body, impairments to skeletal muscle health in T1DM would impact insulin sensitivity, glucose/lipid disposal and basal metabolic rate and thus affect the ability of persons with T1DM to manage their disease. In this review, we discuss the impact of T1DM on skeletal muscle health with a particular focus on the proposed mechanisms involved. We then identify and discuss established and potential adjuvant therapies which, in association with insulin therapy, would improve the health of skeletal muscle in those with T1DM and thereby improve disease management- ultimately delaying the onset and severity of other long-term diabetic complications.

Differential control of muscle mass in type 1 and type 2 diabetes mellitus

Diabetes mellitus--whether driven by insulin deficiency or insulin resistance--causes major alterations in muscle metabolism. These alterations have an impact on nutrient handling, including the metabolism of glucose, lipids, and amino acids, and also on muscle mass and strength. However, the ways in which the distinct forms of diabetes affect muscle mass differ greatly. The most common forms of diabetes mellitus are type 1 and type 2. Thus, whereas type 1 diabetic subjects without insulin treatment display a dramatic loss of muscle, most type 2 diabetic subjects show no changes or even an increase in muscle mass. However, the most commonly used rodent models of type 2 diabetes are characterized by muscle atrophy and do not mimic the features of the disease in humans in terms of muscle mass. In this review, we analyze the processes that are differentially regulated under these forms of diabetes and propose regulatory mechanisms to explain them.

Xin-deficient mice display myopathy, impaired contractility, attenuated muscle repair and altered satellite cell functionality

AIM

Xin is an F-actin-binding protein expressed during development of cardiac and skeletal muscle. We used Xin-/- mice to determine the impact of Xin deficiency on different aspects of skeletal muscle health, including functionality and regeneration.

METHODS

Xin-/- skeletal muscles and their satellite cell (SC) population were investigated for the presence of myopathic changes by a series of histological and immunofluorescent stains on resting uninjured muscles. To further understand the effect of Xin loss on muscle health and its SCs, we studied SCs responses following cardiotoxin-induced muscle injury. Functional data were determined using in situ muscle stimulation protocol.

RESULTS

Compared to age-matched wild-type (WT), Xin-/- muscles exhibited generalized myopathy and increased fatigability with a significantly decreased force recovery post-fatiguing contractions. Muscle regeneration was attenuated in Xin-/- mice. This impaired regeneration prompted an investigation into SC content and functionality. Although SC content was not different, significantly more activated SCs were present in Xin-/- vs. WT muscles. Primary Xin-/- myoblasts displayed significant reductions (approx. 50%) in proliferative capacity vs. WT; a finding corroborated by significantly decreased MyoD-positive nuclei in 3 days post-injury Xin-/- muscle vs. WT. As more activated SCs did not translate to more proliferating myoblasts, we investigated whether Xin-/- SCs displayed an exaggerated loss by apoptosis. More apoptotic SCs (TUNEL+/Pax7+) were present in Xin-/- muscle vs. WT. Furthermore, more Xin-/- myoblasts were expressing nuclear caspase-3 compared to WT at 3 days post-injury.

CONCLUSION

Xin deficiency leads to a myopathic condition characterized by increased muscle fatigability, impaired regeneration and SC dysfunction.

Hyperglycemia induced expression, phosphorylation, and translocation of αB-crystallin in rat skeletal muscle

αB-Crystallin (αBC) is a member of the small heat shock protein family that responds to a variety of stress and prevents the aggregation of partially unfolded proteins. Chronic hyperglycemia created during diabetes results in skeletal muscle atrophy and leads to diabetic myopathy. The aim of this study was to investigate the role of αBC under chronic hyperglycemia in rat skeletal muscle. Diabetes was induced in Wistar rats by a single i.p injection of streptozotocin and maintained for a period of 12 weeks at the end of which the animals were sacrificed and the muscle was collected. The protein levels of αBC and its phosphorylation status in gastrocnemius muscle were analyzed by immunoblotting. The translocation of phosphorylated αBC was analyzed by detergent solubility assay, co-immunoprecipitation (Co-IP), and immunohistochemistry. The cell death was analyzed by TUNEL assay and by apoptotic markers. The interaction of αBC with Bax was analyzed by Co-IP. Chronic hyperglycemia significantly increased the protein levels of αBC and its phosphorylation at S59 by activation of p38 mitogen-activated protein kinase (p38MAPK) and at S45 by activation of the extracellular regulated protein kinase 1/2 (ERK1/2). Further, phosphorylated αBC translocated and interacted with desmin indicating that phosphorylated αBC forms might be involved in protection of sarcomere structures from disruption in chronic hyperglycemia. Further, Co-IP studies showed an impaired interaction of αBC with Bax which could be one of the possible factors for increased cell death as evidenced by TUNEL assay in diabetic muscle. These results suggest that an increased expression, phosphorylation, translocation of αBC, and its involvement in apoptosis might play a significant role in maintenance of cytoskeletal architecture and protection of cells from apoptosis in diabetic skeletal muscle.

Myoblast-conditioned media improve regeneration and revascularization of ischemic muscles in diabetic mice

Introduction

Diabetes is associated with reduced expression of heme oxygenase-1 (HO-1), a heme-degrading enzyme with cytoprotective and proangiogenic properties. In myoblasts and muscle satellite cells HO-1 improves survival, proliferation and production of proangiogenic growth factors. Induction of HO-1 in injured tissues facilitates neovascularization, the process impaired in diabetes. We aimed to examine whether conditioned media from the HO-1 overexpressing myoblast cell line can improve a blood-flow recovery in ischemic muscles of diabetic mice.

Methods

Analysis of myogenic markers was performed at the mRNA level in primary muscle satellite cells, isolated by a pre-plate technique from diabetic db/db and normoglycemic wild-type mice, and then cultured under growth or differentiation conditions. Hind limb ischemia was performed by femoral artery ligation in db/db mice and blood recovery was monitored by laser Doppler measurements. Mice were treated with a single intramuscular injection of conditioned media harvested from wild-type C2C12 myoblast cell line, C2C12 cells stably transduced with HO-1 cDNA, or with unconditioned media.

Results

Expression of HO-1 was lower in muscle satellite cells isolated from muscles of diabetic db/db mice when compared to their wild-type counterparts, what was accompanied by increased levels of Myf5 or CXCR4, and decreased Mef2 or Pax7. Such cells also displayed diminished differentiation potential when cultured in vitro, as shown by less effective formation of myotubes and reduced expression of myogenic markers (myogenic differentiation antigen - myoD, myogenin and myosin). Blood flow recovery after induction of severe hind limb ischemia was delayed in db/db mice compared to that in normoglycemic individuals. To improve muscle regeneration after ischemia, conditioned media collected from differentiating C2C12 cells (control and HO-1 overexpressing) were injected into hind limbs of diabetic mice. Analysis of blood flow revealed that media from HO-1 overexpressing cells accelerated blood-flow recovery, while immunohistochemical staining assessment of vessel density in injected muscle confirmed increased angiogenesis. The effect might be mediated by stromal-cell derived factor-1α proangiogenic factor, as its secretion is elevated in HO-1 overexpressing cells.

Conclusions

In conclusion, paracrine stimulation of angiogenesis in ischemic skeletal muscle using conditioned media may be a safe approach exploiting protective and proangiogenic properties of HO-1 in diabetes.

Fitness and physical activity in youth with type 1 diabetes mellitus in good or poor glycemic control

BACKGROUND

Patients with type 1 diabetes mellitus (T1DM) may experience poor muscle health as a result of chronic hyperglycemia. Despite this, muscle function in children with T1DM with good or poor glycemic control has yet to be examined in detail.

OBJECTIVE

To assess differences in muscle-related fitness variables in children with T1DM with good glycemic control (T1DM-G), as well as those with poor glycemic control (T1DM-P), and non-diabetic, healthy controls.

SUBJECTS

Eight children with T1DM-G [glycosylated hemoglobin (HbA1c) ≤ 7.5% for 9 months], eight children with T1DM-P (HbA1c ≥ 9.0% for 9 months), and eight healthy controls completed one exercise session.

METHODS

Anaerobic and aerobic muscle functions were assessed with a maximal isometric grip strength test, a Wingate test, and an incremental continuous cycling test until exhaustion. Blood samples were collected at rest to determine HbA1c at the time of testing. Physical activity was monitored over 7 d using accelerometry.

RESULTS

Children with T1DM-P displayed lower peak oxygen consumption (VO2peak ) values (mL/kg/min) compared to healthy controls (T1DM-P: 33.2 ± 5.6, controls: 43.5 ± 6.3, p < 0.01), while T1DM-G (43.5 ± 6.3) had values similar to controls and T1DM-P. There was a negative relationship between VO2peak and HbA1c% (r = -0.54, p < 0.01). All groups were similar in all other fitness variables. There were no group differences in physical activity variables.

CONCLUSION

Children with T1DM-G did not display signs of impaired muscle function, while children with T1DM-P have signs of altered aerobic muscle capacity.

Striated muscle fiber size, composition, and capillary density in diabetes in relation to neuropathy and muscle strength

OBJECTIVE

Diabetic polyneuropathy (DPN) leads to progressive loss of muscle strength in the lower extremities due to muscular atrophy. Changes in vascularization occur in diabetic striated muscle; however, the relationship between these changes and DPN is as yet unexplored. The aim of the present study was to evaluate histologic properties and capillarization of diabetic skeletal muscle in relation to DPN and muscle strength.

METHODS

Twenty type 1 and 20 type 2 diabetic (T1D and T2D, respectively) patients underwent biopsy of the gastrocnemic muscle, isokinetic dynamometry at the ankle, electrophysiological studies, clinical examination, and quantitative sensory examinations. Muscle biopsies were stained immunohistochemically and muscle fiber diameter, fiber type distribution, and capillary density determined. Twenty control subjects were also included in the study.

RESULTS

No relationship was found between muscle fiber diameter, muscle fiber type distribution, or capillary density and degree of neuropathy or muscle strength for either patient group. Muscle fiber diameter and the proportion of Type II fibers were greater for T1D patients than both T2D patients and controls. The T2D patients had fewer capillaries per muscle fiber than T1D patients and controls.

CONCLUSIONS

Striated muscle fiber size, muscle fiber distribution, and vascularization are unrelated to DPN and muscle strength in diabetes.

Hyperglycemia Inhibits Recovery From Disuse-Induced Skeletal Muscle Atrophy in Rats

The purpose of this study was to evaluate the effects of hyperglycemia on skeletal muscle recovery following disuse-induced muscle atrophy in rats. Wistar rats were grouped as streptozotocin-induced diabetic rats and non-diabetic rats. Both ankle joints of each rat were immobilized to induce atrophy of the gastrocnemius muscles. After two weeks of immobilization and an additional two weeks of recovery, tail blood and gastrocnemius muscles were isolated. Serial cross sections of muscles were stained for myosin ATPase (pH 4.5) and alkaline phosphatase activity. Serum insulin and muscle insulin-like growth factor-1 (IGF-1) levels were also measured. Serum insulin levels were significantly reduced in the diabetic rats compared to the non-diabetic controls. The diameters of type I, IIa, and IIb myofibers and capillary-to-myofiber ratio in the isolated muscle tissue were decreased after immobilization in both treatments. During the recovery period, these parameters were restored in the non-diabetic rats, but not in the diabetic rats. In addition, muscle IGF-1 levels after recovery increased significantly in the non-diabetic rats, but not in the diabetic rats. We conclude that decreased levels of insulin and IGF-1 and impairment of angiogenesis associated with diabetes might be partly responsible for the inhibition of regrowth in diabetic muscle.

Multichannel EMG-based estimation of fiber conduction velocity during isometric contraction of patients with different stages of diabetic neuropathy

This study compares muscle fiber conduction velocities estimated using surface electromyography during isometric maximal voluntary contraction in different stages of diabetic neuropathy. Eighty-five adults were studied: 16 non-diabetic individuals and 69 diabetic patients classified into four neuropathy stages, defined by a fuzzy expert system: absent (n=26), mild (n=21), moderate (n=11) and severe (n=11). Average muscle fiber conduction velocities of gastrocnemius medialis, tibialis anterior, vastus lateralis and biceps femoris were assessed using linear array electrodes, and were compared by ANOVA. Conduction velocities were significantly decreased in the moderate neuropathy group for the vastus lateralis compared to other groups (from 18% to 21% decrease), and were also decreased in all diabetic groups for the tibialis anterior (from 15% to 20% from control group). Not only the distal anatomical localization of the muscle affects the conduction velocity, but also the proportion of muscle fiber type, where the tibialis anterior with greater type I fiber proportion is affected earlier while the vastus lateralis with greater type II fiber proportion is affected in later stages of the disease. Generally, the muscles of the lower limb have different responsiveness to the effects of diabetes mellitus and show a reduction in the conduction velocity as neuropathy progresses.

Autophagy-regulating TP53INP2 mediates muscle wasting and is repressed in diabetes

A precise balance between protein degradation and synthesis is essential to preserve skeletal muscle mass. Here, we found that TP53INP2, a homolog of the Drosophila melanogaster DOR protein that regulates autophagy in cellular models, has a direct impact on skeletal muscle mass in vivo. Using different transgenic mouse models, we demonstrated that muscle-specific overexpression of Tp53inp2 reduced muscle mass, while deletion of Tp53inp2 resulted in muscle hypertrophy. TP53INP2 activated basal autophagy in skeletal muscle and sustained p62-independent autophagic degradation of ubiquitinated proteins. Animals with muscle-specific overexpression of Tp53inp2 exhibited enhanced muscle wasting in streptozotocin-induced diabetes that was dependent on autophagy; however, TP53INP2 ablation mitigated experimental diabetes-associated muscle loss. The overexpression or absence of TP53INP2 did not affect muscle wasting in response to denervation, a condition in which autophagy is blocked, further indicating that TP53INP2 alters muscle mass by activating autophagy. Moreover, TP53INP2 expression was markedly repressed in muscle from patients with type 2 diabetes and in murine models of diabetes. Our results indicate that TP53INP2 negatively regulates skeletal muscle mass through activation of autophagy. Furthermore, we propose that TP53INP2 repression is part of an adaptive mechanism aimed at preserving muscle mass under conditions in which insulin action is deficient.

Patients with type 1 diabetes oxidize fat at a greater rate than age- and sex-matched controls

INTRODUCTION

Elevated patient blood glucose and exogenous insulin administration may affect substrate oxidation in patients with type 1 diabetes mellitus (T1DM); however, this has not been demonstrated with conviction. We examined substrate oxidation during incremental exercise in a group of subjects with T1DM and compared the results to those of an age- and sex-matched control group of subjects.

METHODS

A group of subjects with T1DM (n = 29; 10 men, 19 women) was recruited for metabolic testing from a weeklong fitness camp. An age- and sex-matched control group of subjects (n = 29; 10 men, 19 women) was recruited from the local community. Subjects were required to avoid strenuous exercise for 48 hours and fast for 2 hours prior to metabolic testing. An incremental test to exhaustion on either a stationary cycle or treadmill was administered to all subjects. Maximum oxygen consumption of subjects was measured (T1DM subjects: 41.4 ± 1.9 mL/kg/min; control subjects: 48.4 ± 1.3 mL/kg/min). Blood glucose was recorded at 20 and 5 minutes before the exercise test, and at 5 and 20 minutes after the exercise test.

RESULTS

The T1DM and control subjects were matched for age, height, weight, and body composition. Subject blood glucose levels were higher in the group of subjects with T1DM than the control group at all times measured (P < 0.001). At all relative intensities of exercise (50%-80% maximum oxygen consumption; P < 0.050), absolute fat oxidation was higher in the group of subjects with T1DM (P < 0.050) and absolute carbohydrate oxidation was higher in the control group.

CONCLUSION

Our data indicate that subjects with T1DM oxidize fat at a higher rate and carbohydrates at a lower rate when compared with age- and sex-matched controls at the same relative intensity of exercise, despite the elevated pre-exercise blood glucose of subjects with T1DM.

Muscle atrophy in aging and chronic diseases: is it sarcopenia or cachexia?

Cachexia and sarcopenia present several analogies in both the pathogenic mechanisms and the clinical picture. The loss of muscle mass and strength is a hallmark of these two clinical conditions. Although frequently overlapping and often indistinguishable, especially in old individuals, these two conditions should be considered distinct clinical entities. A prompt and accurate patient evaluation, guiding the physician through a proper differential diagnostic procedure and providing the best therapeutic options, is recommended. Given the several commonalities between cachexia and sarcopenia, it is likely that the therapeutic approaches may prove effective in both conditions. This review focuses on the most recent available literature and aims at providing physicians with the correct tools that are available to aid in diagnosing these two different entities that often clinically overlap. Currently available or proposed therapeutic strategies for pre-cachexia, cachexia and sarcopenia are also briefly described.

Expression of basic fibroblast growth factor, protein kinase C and members of the apoptotic pathway in skeletal muscle of streptozotocin-induced diabetic rats

This study investigated the potential mechanisms that may underlie diabetes induced amyoatrophy. Sprague-Dawley rats were either injected intraperiotneally with STZ (test group; N=8) to induce diabetic-like symptoms (blood glucose level ≥16.65mmol/L) or with buffer (control group; N=8). Differences in muscle structure between the STZ-induced diabetic and control groups were evaluated by histochemistry. Protein and mRNA levels of basic FGF (bFGF), bax, bcl-2, and caspase 3 in skeletal muscle were compared between the 2 groups using immunohistochemistry and quantitative PCR, respectively. Serum level of insulin and protein kinase C (PKC) were measured by competitive RIA and ELISA, respectively. Unlike control animals, the skeletal muscle fibers from STZ-induced diabetic animals were broken and pyknotic, the sarcomeric structure disrupted, and mild hyperplasia of interstitial adipose tissues was detected. The serum level of PKC was higher (P=0.003) and the protein and mRNA levels of bFGF in skeletal muscle were lower (P=0.001) in STZ-induced diabetic versus control animals. Protein and mRNA levels of the apoptosis promoting genes caspase-3 and bax were higher in skeletal muscle from STZ-induced diabetic rats as compared to control animals (P<0.001 and P=0.037, respectively), while mRNA and protein levels of bcl-2, an inhibitor of apoptosis, was lower in STZ-induced diabetic rats versus control animals (P=0.026). Increasing apoptosis in skeletal muscle from STZ-induced diabetic rats was further demonstrated by TNNEL assay. Our findings suggest that enhanced PKC levels, reduction of bFGF expression, and increased in apoptosis might be associated with the development of diabetes-induced myoatrophy.

Impaired macrophage and satellite cell infiltration occurs in a muscle-specific fashion following injury in diabetic skeletal muscle

BACKGROUND

Systemic elevations in PAI-1 suppress the fibrinolytic pathway leading to poor collagen remodelling and delayed regeneration of tibialis anterior (TA) muscles in type-1 diabetic Akita mice. However, how impaired collagen remodelling was specifically attenuating regeneration in Akita mice remained unknown. Furthermore, given intrinsic differences between muscle groups, it was unclear if the reparative responses between muscle groups were different.

PRINCIPAL FINDINGS

Here we reveal that diabetic Akita muscles display differential regenerative responses with the TA and gastrocnemius muscles exhibiting reduced regenerating myofiber area compared to wild-type mice, while soleus muscles displayed no difference between animal groups following injury. Collagen levels in TA and gastrocnemius, but not soleus, were significantly increased post-injury versus controls. At 5 days post-injury, when degenerating/necrotic regions were present in both animal groups, Akita TA and gastrocnemius muscles displayed reduced macrophage and satellite cell infiltration and poor myofiber formation. By 10 days post-injury, necrotic regions were absent in wild-type TA but persisted in Akita TA. In contrast, Akita soleus exhibited no impairment in any of these measures compared to wild-type soleus. In an effort to define how impaired collagen turnover was attenuating regeneration in Akita TA, a PAI-1 inhibitor (PAI-039) was orally administered to Akita mice following cardiotoxin injury. PAI-039 administration promoted macrophage and satellite cell infiltration into necrotic areas of the TA and gastrocnemius. Importantly, soleus muscles exhibit the highest inducible expression of MMP-9 following injury, providing a mechanism for normative collagen degradation and injury recovery in this muscle despite systemically elevated PAI-1.

CONCLUSIONS

Our findings suggest the mechanism underlying how impaired collagen remodelling in type-1 diabetes results in delayed regeneration is an impairment in macrophage infiltration and satellite cell recruitment to degenerating areas; a phenomena that occurs differentially between muscle groups.

Resistance versus aerobic exercise: acute effects on glycemia in type 1 diabetes

OBJECTIVE

In type 1 diabetes, small studies have found that resistance exercise (weight lifting) reduces HbA(1c). In the current study, we examined the acute impacts of resistance exercise on glycemia during exercise and in the subsequent 24 h compared with aerobic exercise and no exercise.

RESEARCH DESIGN AND METHODS

Twelve physically active individuals with type 1 diabetes (HbA(1c) 7.1 ± 1.0%) performed 45 min of resistance exercise (three sets of seven exercises at eight repetitions maximum), 45 min of aerobic exercise (running at 60% of Vo(2max)), or no exercise on separate days. Plasma glucose was measured during and for 60 min after exercise. Interstitial glucose was measured by continuous glucose monitoring 24 h before, during, and 24 h after exercise.

RESULTS

Treatment-by-time interactions (P < 0.001) were found for changes in plasma glucose during and after exercise. Plasma glucose decreased from 8.4 ± 2.7 to 6.8 ± 2.3 mmol/L (P = 0.008) during resistance exercise and from 9.2 ± 3.4 to 5.8 ± 2.0 mmol/L (P = 0.001) during aerobic exercise. No significant changes were seen during the no-exercise control session. During recovery, glucose levels did not change significantly after resistance exercise but increased by 2.2 ± 0.6 mmol/L (P = 0.023) after aerobic exercise. Mean interstitial glucose from 4.5 to 6.0 h postexercise was significantly lower after resistance exercise versus aerobic exercise.

CONCLUSIONS

Resistance exercise causes less initial decline in blood glucose during the activity but is associated with more prolonged reductions in postexercise glycemia than aerobic exercise. This might account for HbA(1c) reductions found in studies of resistance exercise but not aerobic exercise in type 1 diabetes.

Gender and Contractile Functions of Slow and Fast Skeletal Muscles in Streptozotocin Induced Diabetic Sprague Dawley Rats

Objectives: Diabetes mellitus has been linked with specific morphological andmetabolic abnormalities of skeletal muscle in a fiber specific manner. Aim: Thepresent study was designed to compare the contractile functions of slow and fastskeletal muscles in streptozotocin (STZ) induced diabetic male and female SpragueDawley rats. Material and methods: Thirty healthy Sprague Dawley rats (15 maleand 15 female) were divided into two groups and studied after four weeks followingdiabetes induction. The rats in group I (male diabetic; n = 15) and group II (femalediabetic; n = 15) were fed on normal pellet diet and water ad libitum and rendereddiabetic by single intraperitoneal injection of STZ 65 mg/kg body weight at the startof study (day 1). At the end of four weeks, the contractile parameters of slow soleusand fast extensor digitorum longus (EDL) muscles were recorded by iWorx advancedanimal/human physiology data acquisition unit (AHK/214). Results: At the end offour weeks, the weight of isolated soleus and EDL muscles in the male diabetic ratswas significantly higher (p < 0.001) as compared to the female diabetic rats.However, no significant difference was found in any of the contractile functions ofisolated soleus and EDL muscles when compared between the male and femalediabetic rats. Conclusion: No gender differences exist in the contractile functions ofslow and fast skeletal muscles in streptozotocin induced diabetic Sprague Dawleyrats.

Reduced physical fitness in children and adolescents with type 1 diabetes

AIMS

To evaluate motor performance and cardiorespiratory function in youths with type 1 diabetes in comparison with age-matched control groups and to analyze the influence of physical activity level, anthropometric and physical fitness parameters on long-term metabolic control.

METHODS

106 youths with diabetes and 130 healthy youths aged 8-18 were assessed by the Eurofit test regarding motor performances, cardiorespiratory fitness (VO2max), skinfold thickness, and body mass index. Physical activity level was assessed through the use of questionnaires. Predictors of physical fitness and metabolic control were determined with regression analysis.

RESULTS

There were no differences either in body composition or in physical activity level, but younger girls with diabetes had impaired results in speed of upper limb movement, abdominal muscle strength, upper body strength, running speed, and VO2max ; older girls with diabetes had poor results in speed of upper limb movement, abdominal muscle strength, upper body strength and VO2max . Younger boys with diabetes had impaired results in speed of upper limb movement, flexibility, static strength of hand, and abdominal muscle strength; and older boys with diabetes had poor results in speed of upper limb movement, flexibility, abdominal muscle strength, upper body strength, and VO2max compared with control groups. Older age, female gender, lower physical activity level, and higher HbA1c were significant independent predictors of poorer VO2max. Better VO2max proved to be the single predictor of favorable HbA1c .

CONCLUSIONS

Youths with diabetes have reduced fitness parameters. Efforts should be carried out to improve physical fitness as part of treatment and care of children and adolescents with type 1 diabetes.