Resistance training recovers attenuated APPL1 expression and improves insulin-induced Akt signal activation in skeletal muscle of type 2 diabetic rats

Mechanisms of endurance and resistance exercise in type 2 diabetes mellitus: A Narrative review

In the treatment and management of type 2 diabetes mellitus (T2DM), exercise therapy has received increasing attention due to its accessibility and cost-effectiveness. Regular physical exercise improves glycemic control by ameliorating insulin resistance (IR) and reducing the risk of complications. However, the distinct mechanisms underlying the efficacy of endurance training (ET) and resistance training (RT) in T2DM remain incompletely understood. This review systematically compares the molecular pathways through which ET and RT improve IR, focusing on epigenetic regulation, metabolic reprogramming, and anti-inflammatory effects. We highlight that RT enhances protein synthesis via the IGF-1/PI3K/AKT/mTOR pathway, while ET predominantly improves mitochondrial biogenesis and lipid oxidation through AMPK/SIRT1/PGC-1α signaling. Additionally, ET exerts immunomodulatory effects by suppressing pro-inflammatory cytokines (e.g., TNF-α) and elevating anti-inflammatory myokines (e.g., IL-6). These findings provide a mechanistic basis for personalized exercise prescriptions in T2DM management.

Rapamycin administration causes a decrease in muscle contractile function and systemic glucose intolerance concomitant with reduced skeletal muscle Rictor, the mTORC2 component, expression independent of energy intake in young rats

Emerging evidence suggests the potential of rapamycin, an antibiotic from Streptomyces hygroscopicus that functions as a mechanistic target of rapamycin (mTOR) inhibitor, as a mimetic of caloric restriction (CR) for maintaining skeletal muscle health. Several studies showed that rapamycin administration (RAP) reduced appetite and energy intake. However, the physiological and molecular differences between RAP and CR in skeletal muscle are not fully understood. Here we observed the effects of 4 weeks of RAP administration and CR corresponding to the reduction in energy intake produced by RAP administration (PF, paired feeding) on fast glycolytic and slow oxidative muscle in young adult rats. We found that 4 weeks of RAP demonstrated low fast-glycolytic muscle mass with smaller type I and IIb/x myofiber size independent of the energy intake. In addition, PF improved the contractile function of the plantar flexor muscle, whereas RAP did not improve its function. The suppressing response of mTORC1 signaling to RAP is greater in slow-oxidative muscles than in fast-glycolytic muscles. In addition, systemic glucose tolerance was exacerbated by RAP, with reduced expression of Rictor and hexokinase in skeletal muscle. These observations imply that RAP may have a slight but significant negative impact and it obviously different to CR in young adult skeletal muscle.

Assessment of pathogenicity and functional characterization of APPL1 gene mutations in diabetic patients

BACKGROUND

Adaptor protein, phosphotyrosine interacting with PH domain and leucine zipper 1 (APPL1) plays a crucial role in regulating insulin signaling and glucose metabolism. Mutations in the APPL1 gene have been associated with the development of maturity-onset diabetes of the young type 14 (MODY14). Currently, only two mutations [c.1655T>A (p.Leu552*) and c.281G>A p.(Asp94Asn)] have been identified in association with this disease. Given the limited understanding of MODY14, it is imperative to identify additional cases and carry out comprehensive research on MODY14 and APPL1 mutations.

AIM

To assess the pathogenicity of APPL1 gene mutations in diabetic patients and to characterize the functional role of the APPL1 domain.

METHODS

Patients exhibiting clinical signs and a medical history suggestive of MODY were screened for the study. Whole exome sequencing was performed on the patients as well as their family members. The pathogenicity of the identified APPL1 variants was predicted on the basis of bioinformatics analysis. In addition, the pathogenicity of the novel APPL1 variant was preliminarily evaluated through in vitro functional experiments. Finally, the impact of these variants on APPL1 protein expression and the insulin pathway were assessed, and the potential mechanism underlying the interaction between the APPL1 protein and the insulin receptor was further explored.

RESULTS

A total of five novel mutations were identified, including four missense mutations (Asp632Tyr, Arg633His, Arg532Gln, and Ile642Met) and one intronic mutation (1153-16A>T). Pathogenicity prediction analysis revealed that the Arg532Gln was pathogenic across all predictions. The Asp632Tyr and Arg633His variants also had pathogenicity based on MutationTaster. In addition, multiple alignment of amino acid sequences showed that the Arg532Gln, Asp632Tyr, and Arg633His variants were conserved across different species. Moreover, in in vitro functional experiments, both the c.1894G>T (at Asp632Tyr) and c.1595G>A (at Arg532Gln) mutations were found to downregulate the expression of APPL1 on both protein and mRNA levels, indicating their pathogenic nature. Therefore, based on the patient's clinical and family history, combined with the results from bioinformatics analysis and functional experiment, the c.1894G>T (at Asp632Tyr) and c.1595G>A (at Arg532Gln) mutations were classified as pathogenic mutations. Importantly, all these mutations were located within the phosphotyrosine-binding domain of APPL1, which plays a critical role in the insulin sensitization effect.

CONCLUSION

This study provided new insights into the pathogenicity of APPL1 gene mutations in diabetes and revealed a potential target for the diagnosis and treatment of the disease.

Adiponectin receptor 1 could explain the sex differences in molecular basis of cognitive improvements induced by exercise training in type 2 diabetic rats

Adipokines dysregulation, the main reason for cognitive impairments (CI) induced by diabetes, shows a sex-dependent pattern inherently and in response to exercise. This study aimed to compare the attenuating effect of 8-week high intensity-interval training (HIIT) on type 2 diabetes (T2D)-induced CI between male and female rats with a special focus on adiponectin and leptin. 28 male & 28 female Wistar rats with an average age of 8 weeks were randomly assigned into four groups: control (Con), exercise (EX), Diabetes (T2D), and Type 2 diabetes + exercise (T2D + Ex). Rats in EX and T2D + EX groups performed HIIT for eight weeks (80-100% Vmax, 4-10 intervals). T2D was induced by 2 months of a high-fat diet and a single dose of STZ (35 mg/kg) administration. Leptin and adiponectin levels in serum were measured along with hippocampal expression of leptin and adiponectin receptors, AMP-activated protein kinase (AMPK), dephosphorylated glycogen synthase kinase-3 beta (Dep-GSK3β), Tau, and beta-amyloid (Aβ). Homeostasis model assessments (HOMAs) and quantitative insulin-sensitivity check index (QUICKI) indices were calculated. Our results showed that following T2D, serum levels of APN, and hippocampal levels of adiponectin receptor 1 (APNR1) were higher and HOMA-IR was lower in female than male rats (P < 0.05). However, after 8 weeks of HIIT, hippocampal levels of APNR1 and AMPK as well as QUICKI were lower and hippocampal levels of GSK, Tau, and Aβ were higher in females compared to male rats (P < 0.05). While the risk of CI following T2D was more in male than female rats HIIT showed a more ameliorating effect in male animals with APN1 as the main player.

Integrated transcriptome analysis identifies APPL1/RPS6KB2/GALK1 as immune-related metastasis factors in breast cancer

The aim of this study is to investigate the prognostic immune-related factors in breast cancer (BC) metastasis. The gene expression chip GSE159956 was downloaded from the gene expression omnibus database. Differentially expressed genes (DEGs) were selected using GEO2R online tools based on lymph node and metastasis status. The intersected survival-associated DEGs were screened from the Kaplan-Meier curve. Gene ontology (GO) and Kyoto Encyclopedia of Gene and Genome (KEGG) annotation analyses were performed to determine the survival-associated DEGs. Immune-related prognostic factors were screened based on immune infiltration. The screened prognostic factors were verified by the Cancer Genome Atlas (TCGA) database and single-sample gene set enrichment analysis (ssGSEA). As a result, twenty-eight upregulated and three downregulated genes were generated by the survival analysis. The enriched GO and KEGG pathways were mostly correlated with "regulation of cellular amino acid metabolic process," "proteasome complex," "endopeptidase activity," and "proteasome." Six of 19 (17 upregulated and 2 downregulated) immune-related prognostic factors were verified by the TCGA database. Four immune-related factors were obtained after ssGSEA, and three significant immune-related factors were selected after univariate and multivariate analyses. Based on the risk score receiver operating characteristic, the three immune-related prognosis factors could be potential biomarkers of BC metastasis. In conclusion, APPL1, RPS6KB2, and GALK1 may play a pivotal role as potential biomarkers for prediction of BC metastasis.

A Review of Rehabilitation Benefits of Exercise Training Combined with Nutrition Supplement for Improving Protein Synthesis and Skeletal Muscle Strength in Patients with Cerebral Stroke

Cerebral vascular accident (CVA) is one of the main causes of chronic disability, and it affects the function of daily life, so it is increasingly important to actively rehabilitate patients' physical functions. The research confirmed that the nutrition supplement strategy is helpful to improve the effect of sports rehabilitation adaptation and sports performance. The patients with chronic strokes (whose strokes occur for more than 6 months) have special nutritional needs while actively carrying out rehabilitation exercises, but there are still few studies to discuss at present. Therefore, this paper will take exercise rehabilitation to promote muscle strength and improve muscle protein synthesis as the main axis and, through integrating existing scientific evidence, discuss the special needs of chronic stroke patients in rehabilitation exercise intervention and nutrition supplement one by one. At the same time, we further evaluated the physiological mechanism of nutrition intervention to promote training adaptation and compared the effects of various nutrition supplement strategies on stroke rehabilitation. Literature review pointed out that immediately supplementing protein nutrition (such as whey protein or soybean protein) after resistance exercise or endurance exercise can promote the efficiency of muscle protein synthesis and produce additive benefits, thereby improving the quality of muscle tissue. Recent animal research results show that probiotics can prevent the risk factors of neural function degradation and promote the benefits of sports rehabilitation. At the same time, natural polyphenols (such as catechin or resveratrol) or vitamins can also reduce the oxidative stress injury caused by animal stroke and promote the proliferation of neural tissue. In view of the fact that animal research results still make up the majority of issues related to the role of nutrition supplements in promoting nerve repair and protection, and the true benefits still need to be confirmed by subsequent human studies. This paper suggests that the future research direction should be the supplement of natural antioxidants, probiotics, compound nutritional supplements, and integrated human clinical research.

Co-ingestion of cluster dextrin carbohydrate does not increase exogenous protein-derived amino acid release or myofibrillar protein synthesis following a whole-body resistance exercise in moderately trained younger males: a double-blinded randomized controlled crossover trial

Purpose

This study investigates if co-ingestion of cluster dextrin (CDX) augments the appearance of intrinsically labeled meat protein hydrolysate-derived amino acid (D₅-phenylalanine), Akt/mTORC1 signaling, and myofibrillar protein fractional synthetic rate (FSR).

Methods

Ten moderately trained healthy males (age: 21.5 ± 2.1 years, body mass: 75.7 ± 7.6 kg, body mass index (BMI): 22.9 ± 2.1 kg/m²) were included for a double-blinded randomized controlled crossover trial. Either 75 g of CDX or glucose (GLC) was given in conjunction with meat protein hydrolysate (0.6 g protein * FFM⁻¹) following a whole-body resistance exercise. A primed-continuous intravenous infusion of L-[¹⁵N]-phenylalanine with serial muscle biopsies and venous blood sampling was performed.

Results

A time × group interaction effect was found for serum D₅-phenylalanine enrichment (P < 0.01). Serum EAA and BCAA concentrations showed a main effect for group (P < 0.05). T_max serum BCAA was greater in CDX as compared to GLC (P < 0.05). However, iAUC of all serum parameters did not differ between CDX and GLC (P > 0.05). T_max serum EAA showed a trend towards a statistical significance favoring CDX over GLC. The phosphorylation of p70S6K^Thr389, rpS6^Ser240/244, ERK1/2^{Thr202/Tyr204} was greater in CDX compared to GLC (P < 0.05). However, postprandial myofibrillar FSR did not differ between CDX and GLC (P = 0.17).

Conclusion

In moderately trained younger males, co-ingestion of CDX with meat protein hydrolysate does not augment the postprandial amino acid availability or myofibrillar FSR as compared to co-ingestion of GLC during the recovery from a whole-body resistance exercise despite an increased intramuscular signaling.

Trial registration

ClinicalTrials.gov ID: NCT03303729 (registered on October 3, 2017).

ER-Mitochondria Contacts and Insulin Resistance Modulation through Exercise Intervention

The endoplasmic reticulum (ER) makes physical contacts with mitochondria at specific sites, and the hubs between the two organelles are called mitochondria-associated ER membranes (MAMs). MAMs are known to play key roles in biological processes, such as intracellular Ca²⁺ regulation, lipid trafficking, and metabolism, as well as cell death, etc. Studies demonstrated that dysregulation of MAMs significantly contributed to insulin resistance. Alterations of MAMs’ juxtaposition and integrity, impaired expressions of insulin signaling molecules, disruption of Ca²⁺ homeostasis, and compromised metabolic flexibility are all actively involved in the above processes. In addition, exercise training is considered as an effective stimulus to ameliorate insulin resistance. Although the underlying mechanisms for exercise-induced improvement in insulin resistance are not fully understood, MAMs may be critical for the beneficial effects of exercise.

The Role of Atypical Cannabinoid Ligands O-1602 and O-1918 on Skeletal Muscle Homeostasis with a Focus on Obesity

O-1602 and O-1918 are atypical cannabinoid ligands for GPR55 and GPR18, which may be novel pharmaceuticals for the treatment of obesity by targeting energy homeostasis regulation in skeletal muscle. This study aimed to determine the effect of O-1602 or O-1918 on markers of oxidative capacity and fatty acid metabolism in the skeletal muscle. Diet-induced obese (DIO) male Sprague Dawley rats were administered a daily intraperitoneal injection of O-1602, O-1918 or vehicle for 6 weeks. C₂C₁₂ myotubes were treated with O-1602 or O-1918 and human primary myotubes were treated with O-1918. GPR18 mRNA was expressed in the skeletal muscle of DIO rats and was up-regulated in red gastrocnemius when compared with white gastrocnemius. O-1602 had no effect on mRNA expression on selected markers for oxidative capacity, fatty acid metabolism or adiponectin signalling in gastrocnemius from DIO rats or in C₂C₁₂ myotubes, while APPL2 mRNA was up-regulated in white gastrocnemius in DIO rats treated with O-1918. In C₂C₁₂ myotubes treated with O-1918, PGC1α, NFATc1 and PDK4 mRNA were up-regulated. There were no effects of O-1918 on mRNA expression in human primary myotubes derived from obese and obese T2DM individuals. In conclusion, O-1602 does not alter mRNA expression of key pathways important for skeletal muscle energy homeostasis in obesity. In contrast, O-1918 appears to alter markers of oxidative capacity and fatty acid metabolism in C₂C₁₂ myotubes only. GPR18 is expressed in DIO rat skeletal muscle and future work could focus on selectively modulating GPR18 in a tissue-specific manner, which may be beneficial for obesity-targeted therapies.

Enhanced skeletal muscle insulin sensitivity after acute resistance-type exercise is upregulated by rapamycin-sensitive mTOR complex 1 inhibition

Acute aerobic exercise (AE) increases skeletal muscle insulin sensitivity for several hours, caused by acute activation of AMP-activated protein kinase (AMPK). Acute resistance exercise (RE) also activates AMPK, possibly improving insulin-stimulated glucose uptake. However, RE-induced rapamycin-sensitive mechanistic target of rapamycin complex 1 (mTORC1) activation is higher and has a longer duration than after AE. In molecular studies, mTORC1 was shown to be upstream of insulin receptor substrate 1 (IRS-1) Ser phosphorylation residue, inducing insulin resistance. Therefore, we hypothesised that although RE increases insulin sensitivity through AMPK activation, prolonged mTORC1 activation after RE reduces RE-induced insulin sensitising effect. In this study, we used an electrical stimulation-induced RE model in rats, with rapamycin as an inhibitor of mTORC1 activation. Our results showed that RE increased insulin-stimulated glucose uptake following AMPK signal activation. However, mTORC1 activation and IRS-1 Ser632/635 and Ser612 phosphorylation were elevated 6 h after RE, with concomitant impairment of insulin-stimulated Akt signal activation. By contrast, rapamycin inhibited these prior exercise responses. Furthermore, increases in insulin-stimulated skeletal muscle glucose uptake 6 h after RE were higher in rats with rapamycin treatment than with placebo treatment. Our data suggest that mTORC1/IRS-1 signaling inhibition enhances skeletal muscle insulin-sensitising effect of RE.

APPL1 knockdown blocks adipogenic differentiation and promotes adipocyte lipolysis

Adipocyte dysfunction is closely associated with the development of obesity, insulin resistance, and type 2 diabetes. In addition to having a positive effect on adiponectin pathway and insulin signaling through direct and/or indirect mechanisms, adapter protein APPL1 has also been reported to regulate body weight, brown fat tissues thermogenesis, and body fat distribution in diabetic individuals. However, there is dearth of data on the specific role of APPL1 on adipogenic differentiation and adipocyte lipolysis. In this study, APPL1's function in adipocyte differentiation and adipocyte lipolysis was evaluated, and the possible mechanisms were investigated. We found that APPL1 knockdown (KD) impeded differentiation of 3T3-L1 preadipocytes into mature 3T3-L1 adipocytes and enhanced basal and insulin-suppressed lipolysis in mature 3T3-L1 adipocytes. APPL1 KD cells presented a reduced autophagic activity in 3T3-L1 preadipocytes and mature 3T3-L1 adipocytes. In 3T3-L1 preadipocytes, APPL1 KD reduced PPARγ protein levels, which was prevented by administration with proteasome inhibitor MG132. Furthermore, APPL1 KD-reduced autophagic activity in mature 3T3-L1 adipocytes was markedly restored by inhibition of PKA, accompanied with prevention of APPL1-induced lipolysis. In addition, APPL1 KD caused insulin resistance in mature 3T3-L1 adipocytes. Unexpectedly, we found that APPL1 overexpression did not appear to play a role in adipogenic differentiation and adipocyte lipolysis. Our results confirmed that APPL1 KD inhibits adipogenic differentiation by suppressing autophagy and enhances adipocyte lipolysis through activating PKA respectively. These findings may deepen our understanding of APPL1 function, especially its regulation on adipocyte biology.

Type 2 diabetes causes skeletal muscle atrophy but does not impair resistance training-mediated myonuclear accretion and muscle mass gain in rats

New Findings

What is the central question of this study?

Type 2 diabetes mellitus (T2DM) causes skeletal muscle atrophy; does it affect resistance training (RT)‐mediated molecular adaptations and subsequent muscle hypertrophy?

What is the main finding and its importance?

Although skeletal muscle mass and regulation were not preserved under conditions of T2DM, the response of RT‐induced skeletal muscle hypertrophy was not impaired in T2DM rat skeletal muscle. These findings suggest that the capacity of RT‐mediated muscle mass gain is not diminished in the T2DM condition.

Abstract

Type 2 diabetes mellitus (T2DM) is known to cause skeletal muscle atrophy. However, it is not known whether T2DM affects resistance training (RT)‐mediated molecular adaptations and subsequent muscle hypertrophy. Therefore, we investigated the effect of T2DM on response of skeletal muscle hypertrophy to chronic RT using a rat resistance exercise mimetic model. T2DM and healthy control rats were subjected to 18 bouts (3 times per week) of chronic RT on unilateral lower legs. RT significantly increased gastrocnemius muscle mass and myonuclei in both T2DM and healthy control rats to the same extent, even though T2DM caused muscle atrophy in the resting condition. Further, T2DM significantly reduced mechanistic target of rapamycin complex 1 (mTORC1) activity (phosphorylation of p70S6K^Thr389 and 4E‐BP1^Thr37/46) to insulin stimulation and the number of myonuclei in the untrained basal condition, but RT‐mediated adaptations were not affected by T2DM. These findings suggested that although the skeletal muscle mass and regulation were not preserved under basal conditions of T2DM, the response of RT‐induced skeletal muscle hypertrophy was not impaired in T2DM rat skeletal muscle.

The effects of resistance training on bone mineral density and bone quality in type 2 diabetic rats

Resistance training (RT) has been known to be effective in maintaining and improving bone strength, which is based on bone mineral density (BMD) and bone quality. However, it is not clear whether RT is effective in improving bone strength in patients with type-2 diabetes mellitus (T2DM), who have a high risk of fracture. Therefore, we tested the effects of a 6-week RT regimen using percutaneous electrical stimulation in T2DM model rats, male Otsuka Long-Evans Tokushima Fatty (OLETF), and its control, Long-Evans Tokushima Otsuka (LETO). After 6 weeks of RT, tibial BMD in RT legs was significantly higher than that in control (CON) legs in both groups. In diaphyseal cortical bone, bone area/tissue area, and cortical thickness was significantly increased in RT legs compared with CON legs in both groups. Cortical porosity was highly observed in OLETF compared with LETO, but RT improved cortical porosity in both groups. Interestingly, trabecular number, trabecular thickness and trabecular space as well as BMD and bone volume/tissue volume in proximal tibial metaphyseal trabecular bone were significantly improved in RT legs compared with CON legs in both groups. In contrast, connectivity density and structural model index were not affected by RT. These results indicate that the 6-week RT regimen effectively increased BMD and improved bone quality in T2DM model rats as well as control rats. Therefore, RT may have the potential to improve bone strength and reduce fracture risk, even in patients with T2DM.