Diabetic Myopathy and Mechanisms of Disease

Hyperglycemia Negatively Affects IPSC-Derived Myoblast Proliferation and Skeletal Muscle Regeneration and Function

Diabetic myopathy is a co-morbidity diagnosed in most diabetes mellitus patients, yet its pathogenesis is still understudied, which hinders the development of effective therapies. This project aimed to investigate the effect of hyperglycemia on human myoblast physiology, devoid of other complicating factors, by utilizing human myoblasts derived from induced pluripotent stem cells (iPSCs), in a defined in vitro system. IPSC-derived myoblasts were expanded under three glucose conditions: low (5 mM), medium (17.5 mM) or high (25 mM). While hyperglycemic myoblasts demonstrated upregulation of Glut4 relative to the euglycemic control, myoblast proliferation demonstrated a glucose dose-dependent impedance. Further cellular analysis revealed a retarded cell cycle progression trapped at the S phase and G2/M phase and an impaired mitochondrial function in hyperglycemic myoblasts. Terminal differentiation of these hyperglycemic myoblasts resulted in significantly hypertrophic and highly branched myotubes with disturbed myosin heavy chain arrangement. Lastly, functional assessment of these myofibers derived from hyperglycemic myoblasts demonstrated comparatively increased fatigability. Collectively, the hyperglycemic myoblasts demonstrated deficient muscle regeneration capability and functionality, which falls in line with the sarcopenia symptoms observed in diabetic myopathy patients. This human-based iPSC-derived skeletal muscle hyperglycemic model provides a valuable platform for mechanistic investigation of diabetic myopathy and therapeutic development.

Rehabilitation of Individuals With Diabetes Mellitus: Focus on Diabetic Myopathy

Diabetes mellitus (DM) is a chronic metabolic disease characterized by high blood glucose levels, causing serious damage to the cardiovascular, respiratory, renal and other systems. The prevalence of type 2 diabetes mellitus (T2DM) was 6.28% in 2017, considering all age groups worldwide (prevalence rate of 6,059 cases per 100,000), and its global prevalence is projected to increase to 7,079 cases per 100,000 by 2030. Furthermore, these individuals are often affected by diabetic myopathy, which is the failure to preserve muscle mass and function in the course of DM. This happens in type 1 diabetes mellitus (T1DM) and T2DM. As skeletal muscle plays a key role in locomotion and glucose homeostasis, diabetic myopathy may contribute to additional complications of the disease. In addition, chronic hyperglycemia is associated with lung functional changes seen in patients with DM, such as reduced lung volumes and compliance, inspiratory muscle strength, and lung elastic recoil. Thus, the weakness of the inspiratory muscles, a consequence of diabetic myopathy, can influence exercise tolerance. Thus, moderate strength training in T2DM can contribute to the gain of peripheral muscle strength. Although the literature is robust on the loss of mass and consequent muscle weakness in diabetic myopathy, triggering pathophysiological factors, the impact on functional capacity, as well as the prescription of physical exercise for this condition deserves to be further explored. This review aims to explore the consequences of diabetic myopathy and its implication in rehabilitation from prescription to safety in the practice of physical exercises for these individuals.

The effects of different doses of exercise on pancreatic β-cell function in patients with newly diagnosed type 2 diabetes: study protocol for and rationale behind the "DOSE-EX" multi-arm parallel-group randomised clinical trial

BACKGROUND

Lifestyle intervention, i.e. diet and physical activity, forms the basis for care of type 2 diabetes (T2D). The current physical activity recommendation for T2D is aerobic training for 150 min/week of moderate to vigorous intensity, supplemented with resistance training 2-3 days/week, with no more than two consecutive days without physical activity. The rationale for the recommendations is based on studies showing a reduction in glycated haemoglobin (HbA1c). This reduction is supposed to be caused by increased insulin sensitivity in muscle and adipose tissue, whereas knowledge about effects on abnormalities in the liver and pancreas are scarce, with the majority of evidence stemming from in vitro and animal studies. The aim of this study is to investigate the role of the volume of exercise training as an adjunct to dietary therapy in order to improve the pancreatic β-cell function in T2D patients less than 7 years from diagnosis. The objective of this protocol for the DOSE-EX trial is to describe the scientific rationale in detail and to provide explicit information about study procedures and planned analyses.

METHODS/DESIGN

In a parallel-group, 4-arm assessor-blinded randomised clinical trial, 80 patients with T2D will be randomly allocated (1:1:1:1, stratified by sex) to 16 weeks in either of the following groups: (1) no intervention (CON), (2) dietary intervention (DCON), (3) dietary intervention and supervised moderate volume exercise (MED), or (4) dietary intervention and supervised high volume exercise (HED). Enrolment was initiated December 15th, 2018, and will continue until N = 80 or December 1st, 2021. Primary outcome is pancreatic beta-cell function assessed as change in late-phase disposition index (DI) from baseline to follow-up assessed by hyperglycaemic clamp. Secondary outcomes include measures of cardiometabolic risk factors and the effect on subsequent complications related to T2D. The study was approved by The Scientific Ethical Committee at the Capital Region of Denmark (H-18038298).

TRIAL REGISTRATION

The Effects of Different Doses of Exercise on Pancreatic β-cell Function in Patients With Newly Diagnosed Type 2 Diabetes (DOSE-EX), NCT03769883, registered 10 December 2018 https://clinicaltrials.gov/ct2/show/NCT03769883 ). Any modification to the protocol, study design, and changes in written participant information will be approved by The Scientific Ethical Committee at the Capital Region of Denmark before effectuation.

DISCUSSION

The data from this study will add knowledge to which volume of exercise training in combination with a dietary intervention is needed to improve β-cell function in T2D. Secondarily, our results will elucidate mechanisms of physical activity mitigating the development of micro- and macrovascular complications correlated with T2D.

Alterations in the structural characteristics of rectus abdominis muscles caused by diabetes and pregnancy: A comparative study of the rat model and women

BACKGROUND AND OBJECTIVE

In the present study, we compared the effect of diabetic pregnancy on the rectus abdominis muscle (RAM) in humans and rats. We hypothesized that our animal model could provide valuable information about alterations in the RAM of women with Gestational Diabetes (GDM).

METHOD

Newborns female rats (n = 10/group) were administered streptozotocin (100 mg/kg body weight) subcutaneously and were mated on reaching adulthood, to develop the mild hyperglycemic pregnant (MHP) rat model. At the end of pregnancy, the mothers were sacrificed, and the RAM tissue was collected. Pregnant women without GDM (non-GDM group; n = 10) and those diagnosed with GDM (GDM group; n = 8) and undergoing treatment were recruited, and RAM samples were obtained at C-section. The RAM architecture and the distribution of the fast and slow fibers and collagen were studied by immunohistochemistry.

RESULTS

No statistically significant differences in the maternal and fetal characters were observed between the groups in both rats and women. However, significant changes in RAM architecture were observed. Diabetes in pregnancy increased the abundance of slow fibers and decreased fast fiber number and area in both rats and women. A decrease in collagen distribution was observed in GDM women; however, a similar change was not observed in the MHP rats.

CONCLUSION

Our results indicated that pregnancy- associated diabetes- induced similar structural adaptations in the RAM of women and rats with slight alterations in fiber type number and area. These findings suggest that the MHP rat model can be used for studying the effects of pregnancy-associated diabetes on the fiber structure of RAM.

Association between Lower Extremity Skeletal Muscle Mass and Impaired Cognitive Function in Type 2 Diabetes

Lower extremity skeletal muscle mass (LESM) in Type 2 Diabetes (T2D) has been linked to adverse clinical events, but it is not known whether it is associated with cognitive difficulties. We conducted a cross-sectional study on 1,235 people (mean age 61.4 ± 8.0 years) with T2D under primary and secondary care in Singapore. Bioelectrical impedance analyses (BIA) measures of upper extremity skeletal muscle mass (UESM), LESM and appendicular skeletal muscle index (SMI) were related to the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) measures of cognition, in multiple linear regression. In multivariable models, tertile 1 LESM (b = −2.62 (−3.92 to −1.32)) and tertile 2 LESM (b = −1.73 (−2.73 to −0.73)), referenced to tertile 3) were significantly associated with decreased RBANS total score. Significant associations of LESM with cognitive domain performances were observed for tertile 1 (b = −3.75 (−5.98 to −1.52)) and tertile 2 (b = −1.98 (−3.69 to −0.27)) with immediate memory, and for tertile 1 (b = −3.05 (−4.86 to −1.24)) and tertile 2 (b = −1.87 (−3.25 to −0.48)) with delayed memory, and for tertile 1 (b = −2.99 (−5.30 to −0.68)) with visuospatial/constructional ability. Tertile 1 SMI (b = −1.94 (−3.79 to −0.08) and tertile 2 SMI (b = −1.75 (−3.14 to −0.37)) were also associated with delayed memory. There were no associations between UESM with cognitive performance. Lower LESM may be a useful marker of possible co-occuring cognitive dysfunction.

Emerging roles of RNA-binding proteins in diabetes and their therapeutic potential in diabetic complications

Diabetes is a debilitating health care problem affecting 422 million people around the world. Diabetic patients suffer from multisystemic complications that can cause mortality and morbidity. Recent advancements in high-throughput next-generation RNA-sequencing and computational algorithms led to the discovery of aberrant posttranscriptional gene regulatory programs in diabetes. However, very little is known about how these regulatory programs are mis-regulated in diabetes. RNA-binding proteins (RBPs) are important regulators of posttranscriptional RNA networks, which are also dysregulated in diabetes. Human genetic studies provide new evidence that polymorphisms and mutations in RBPs are linked to diabetes. Therefore, we will discuss the emerging roles of RBPs in abnormal posttranscriptional gene expression in diabetes. Questions that will be addressed are: Which posttranscriptional mechanisms are disrupted in diabetes? Which RBPs are responsible for such changes under diabetic conditions? How are RBPs altered in diabetes? How does dysregulation of RBPs contribute to diabetes? Can we target RBPs using RNA-based methods to restore gene expression profiles in diabetic patients? Studying the evolving roles of RBPs in diabetes is critical not only for a comprehensive understanding of diabetes pathogenesis but also to design RNA-based therapeutic approaches for diabetic complications. WIREs RNA 2018, 9:e1459. doi: 10.1002/wrna.1459 This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing Translation > Translation Regulation.

Developmentally regulated alternative splicing is perturbed in type 1 diabetic skeletal muscle

INTRODUCTION

Type 1 diabetic patients can develop skeletal muscle weakness and atrophy by molecular mechanisms that are not well understood. Alternative splicing (AS) is critical for gene expression in the skeletal muscle, and its dysregulation is implicated in muscle weakness and atrophy. Therefore, we investigated whether AS patterns are affected in type 1 diabetic skeletal muscle contributing to skeletal muscle defects.

METHODS

AS patterns were determined by reverse transcription-polymerase chain reaction and levels of RNA binding proteins were assessed by Western blot in type 1 diabetic mouse skeletal muscle and during normal mouse skeletal muscle development.

RESULTS

Five genes with critical functions in the skeletal muscle are misspliced in type 1 diabetic skeletal muscle, resembling their AS patterns at embryonic stages. AS of these genes undergoes dramatic transitions during skeletal muscle development, correlating with changes in specific RNA binding proteins.

CONCLUSION

Embryonic spliced variants are inappropriately expressed in type 1 diabetic skeletal muscle. Muscle Nerve 56: 744-749, 2017.

Acute Elevated Glucose Promotes Abnormal Action Potential-Induced Ca2+ Transients in Cultured Skeletal Muscle Fibers

A common comorbidity of diabetes is skeletal muscle dysfunction, which leads to compromised physical function. Previous studies of diabetes in skeletal muscle have shown alterations in excitation-contraction coupling (ECC)-the sequential link between action potentials (AP), intracellular Ca²⁺ release, and the contractile machinery. Yet, little is known about the impact of acute elevated glucose on the temporal properties of AP-induced Ca²⁺ transients and ionic underlying mechanisms that lead to muscle dysfunction. Here, we used high-speed confocal Ca²⁺ imaging to investigate the temporal properties of AP-induced Ca²⁺ transients, an intermediate step of ECC, using an acute in cellulo model of uncontrolled hyperglycemia (25 mM, 48 h.). Control and elevated glucose-exposed muscle fibers cultured for five days displayed four distinct patterns of AP-induced Ca²⁺ transients (phasic, biphasic, phasic-delayed, and phasic-slow decay); most control muscle fibers show phasic AP-induced Ca²⁺ transients, while most fibers exposed to elevated D-glucose displayed biphasic Ca²⁺ transients upon single field stimulation. We hypothesize that these changes in the temporal profile of the AP-induced Ca²⁺ transients are due to changes in the intrinsic excitable properties of the muscle fibers. We propose that these changes accompany early stages of diabetic myopathy.