The effect of acute exercise on GLUT4 levels in peripheral blood mononuclear cells of sled dogs

Fluorescence Microscopy-Based Quantitation of GLUT4 Translocation

Postprandial insulin-stimulated glucose uptake into target tissue is crucial for the maintenance of normal blood glucose homeostasis. This step is rate-limited by the number of facilitative glucose transporters type 4 (GLUT4) present in the plasma membrane. Since insulin resistance and impaired GLUT4 translocation are associated with the development of metabolic disorders such as type 2 diabetes, this transporter has become an important target of antidiabetic drug research. The application of screening approaches that are based on the analysis of GLUT4 translocation to the plasma membrane to identify substances with insulinomimetic properties has gained global research interest in recent years. Here, we review methods that have been implemented to quantitate the translocation of GLUT4 to the plasma membrane. These methods can be broadly divided into two sections: microscopy-based technologies (e.g., immunoelectron, confocal or total internal reflection fluorescence microscopy) and biochemical and spectrometric approaches (e.g., membrane fractionation, photoaffinity labeling or flow cytometry). In this review, we discuss the most relevant approaches applied to GLUT4 thus far, highlighting the advantages and disadvantages of these approaches, and we provide a critical discussion and outlook into new methodological opportunities.

Less is more? Ultra-low carbohydrate diet and working dogs' performance

New Zealand farm working dogs are supreme athletes that are crucial to agriculture in the region. The effects that low or high dietary carbohydrate (CHO) content might have on their interstitial glucose (IG) and activity during work are unknown. The goals of the study were to determine if the concentration of IG and delta-g (a measurement of activity) will be lower in dogs fed an ultra-low CHO high fat diet in comparison to dogs fed a high CHO low fat diet, and to determine if low concentrations of IG are followed by reduced physical activity. We hypothesized that feeding working farm dogs an ultra-low CHO diet would reduce their IG concentrations which in turn would reduce physical activity during work. We prospectively recruited 22 farm dogs from four farms. At each farm, dogs were randomized to one of two diets and had a month of dietary acclimation to their allocated diet. The macronutrient proportions as a percentage of metabolizable energy (%ME) for the high CHO low fat diet (Diet 1) were 23% protein, 25% fat, and 52% CHO, and for the ultra-low CHO high fat diet (Diet 2) 37% protein, 63% fat, and 1% CHO. Following the acclimation period, we continuously monitored IG concentrations with flash glucose monitoring devices, and delta-g using triaxial accelerometers for 96 h. Dogs fed Diet 2 had a lower area under the curve (±SE) for IG (AUC _{Diet 2} = 497 ± 4 mmol/L/96h, AUC _{Diet 1} = 590 ± 3 mmol/L/96h; P = 0.002) but a higher area under the curve (±SE) for delta-g (AUC _{Diet 2} = 104,122 ± 6,045 delta-g/96h, AUC _{Diet 1} = 80,904 ± 4,950 delta-g/96h; P< 0.001). Interstitial glucose concentrations increased as the activity level increased (P < 0.001) and were lower for Diet 2 within each activity level (P < 0.001). The overall incidence of low IG readings (< 3.5 mmol/L) was 119/3810 (3.12%), of which 110 (92.4%) readings occurred in the Diet 2 group (P = 0.001). In the Diet 2 group, 99/110 (90%) of the low IG events occurred during the resting period (19:00–06:00). We conclude that feeding Diet 2 (ultra-low CHO high fat diet) to working farm dogs was associated with increased delta-g despite decreased IG concentrations. Interstitial glucose concentrations were positively associated with dogs’ activity levels independent of diet. Lastly, events of low IG occurred at a low incidence and were predominantly seen between 19:00–06:00 in dogs fed the ultra-low CHO high fat diet.

Gene expression profile of peripheral blood mononuclear cells in mild to moderate obesity in dogs

Background

Molecular mechanisms and early diagnosis on the development of mild to moderate of canine obesity are not understood although recent dog obesity is a widespread problem. To understand the differences between normal weight and mild to moderate obesity, the purpose of this study is to investigate the gene expression profiles of peripheral blood mononuclear cells (PBMC) in dogs.

Methods

This study comprised a sample of 12 privately-owned Miniature Dachshund, which were divided into two groups (obese and control) based on body condition scores (BCS). Serum biochemical parameters and PBMC gene expression profiles were compared between groups.

Results

A statistically significant between group differences was recorded for body weight (BW), BCS, serum Insulin and triglyceride (TG) levels (p < 0.05). RNA-seq revealed the upregulated 154 genes and the downregulated 198 genes in obese dogs at more than 3.5-fold change compared with control animals. Hemoglobin subunits alpha- and beta-like were detected in the downregulated genes. RT-PCR analysis showed downregulation of FOLH1, ALAS2 and LOC100855540 genes, and upregulation of BCL2L15 gene, suggesting that the metabolic difference between normal and mild to moderate obesity was involved in the hemoglobin metabolism.

Conclusions

This study revealed significant differences in the gene expression of BCL2L15, FOLH1, ALAS2, and hemoglobin subunits such as LOC100855540 between normal weight and mild to moderate obese dogs, which indicate that these genes may prevent the obesity in dogs and be potentially useful for diagnosis of mild to moderate obesity.

Changes in physiological, haematological and biochemical parameters in police working dogs during a treadmill incremental exercise test

This study aimed to evaluate the physiological, haematological and biochemical changes during a treadmill incremental exercise test (IET). Animals were submitted to five stages of 6 min each, at 6, 7, 8, 9 and 10 mph, at an inclination of 5%. Blood samples were collected at rest (T0), immediately after exercise (T5) and after a 20 min rest period (T6), to determine complete blood count, urea, creatinine, creatine kinase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, total plasma protein, albumin, alkaline phosphatase (AP), cholesterol, triglycerides (Trig), Ca2+, Na+, K+ and Cl-. Blood lactate (BL), heart rate (HR), rectal temperature (RT) and glycaemia were measured at rest (T0), after each stage (T1-T5) and after the rest period (T6). Variations were recorded between T0 and T5 in red blood cells, haemoglobin, AP, Na+, K+ (P<0.01), Trig (P<0.05), Ca2+ and Cl- (P<0.02). Differences were observed in BL at T5 (P<0.02) and T6 (P<0.02), RT at T2-T6 (P<0.01), HR at T3-T5 (P<0.01) and glycaemia at T2-T4 (P<0.01) and T5 (P<0.05). This study is a novel description of the shifts of physical fit police working dogs during this IET protocol.

Exercise Increases Glucose Transporter-4 Levels on Peripheral Blood Mononuclear Cells

PURPOSE

Glucose transporter 4 (GLUT4) plays a key role in the pathophysiology of type 2 diabetes. Glucose transporter 4 is upregulated in response to exercise, enhancing cellular glucose transport in skeletal muscle tissue. This mechanism appears to remain intact in individuals with insulin resistance. Details of the mechanism are poorly understood and are challenging to study due to the invasive nature of muscle biopsy. Peripheral blood mononuclear cells (PBMC) have documented insulin-sensitive GLUT4 activity and may serve as a proxy tissue for studying skeletal muscle GLUT4. The purpose of this study was to investigate whether GLUT4 in PBMC is affected by conditioning.

METHODS

We recruited 16 student athletes from the cross-country running and skiing teams and fifteen sedentary students matched for age and sex from the University of Alaska Fairbanks. Peripheral blood mononuclear cells were collected with mononuclear cell separation tubes. The GLUT4 concentrations were measured using a commercially available enzyme linked immunosorbent assay. Additionally, correlations between PBMC GLUT4 and common indicators of insulin resistance were examined.

RESULTS

Results indicate significantly higher PBMC GLUT4 levels in conditioned athletes than in their sedentary counterparts, similar to what has been documented in myocytes. Females were observed to have higher PBMC GLUT4 levels than males. Correlations were not detected between PBMC GLUT4 and hemoglobin A1c, glucose, insulin, homeostatic model assessment of insulin resistance, body mass index, or body fat.

CONCLUSIONS

This study provides evidence to support exploration of PBMC as a proxy tissue for studying GLUT4 response to exercise or other noninsulin factors.

Physiological, haematological and biochemical shifts in police working dogs during a riot control exercise

The aim of this study was to evaluate the physiological, haematological and biochemical shifts that occur in police working dogs during a riot control exercise. The animals (n=17) used were dogs from the Guarda Nacional Republicana (Portuguese Gerndarmerie Unit). Heart rate (HR), respiratory rate (RR) and rectal temperature (RT) were measured and blood samples collected, both before (T0) and immediately after (T1) the exercise. Blood lactate (BL) and blood glucose concentration levels were immediately measured using handheld portable devices and from the blood samples the following parameters were determined: red blood cells, haematocrit, white blood cells, platelets, urea, creatinine, creatine phosphokinase, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, total protein, albumin, Ca2+, Na+, K+ and Cl-. Results were submitted to a paired T-test and Pearson correlation coefficient was used to compare different variables. Significant increases occurred in RT (P<0.01), RR (P<0.01), lymphocytes (P<0.05) and creatinine (P<0.05). Other measured parameters showed non-significant variations and no correlation was found between BL and HR and RT – the parameters that can be easily monitored during exercise. The present results consist, to the authors’ knowledge, the first description of the physiological, haematological and biochemical shifts in police working dogs during a riot control exercise. They provide valuable information for the monitoring and future evaluations of this type of work that many police working dogs undergo throughout the world and set a starting point for future studies.

Muscle pathology, limb strength, walking gait, respiratory function and neurological impairment establish disease progression in the p.N155K canine model of X-linked myotubular myopathy

BACKGROUND

Loss-of-function mutations in the myotubularin (MTM1) gene cause X-linked myotubular myopathy (XLMTM), a fatal, inherited pediatric disease that affects the entire skeletal musculature. Labrador retriever dogs carrying an MTM1 missense mutation exhibit strongly reduced synthesis of myotubularin, the founder member of a lipid phosphatase required for normal skeletal muscle function. The resulting canine phenotype resembles that of human patients with comparably severe mutations, and survival does not normally exceed 4 months.

METHODS

We studied MTM1 mutant dogs (n=7) and their age-matched control littermates (n=6) between the ages of 10 and 25 weeks. Investigators blinded to the animal identities sequentially measured limb muscle pathology, fore- and hind limb strength, walking gait, respiratory function and neurological impairment.

RESULTS

MTM1-mutant puppies display centrally-nucleated myofibers of reduced size and disrupted sarcotubular architecture progressing until the end of life, an average of 17 weeks. In-life measures of fore- and hind limb strength establish the rate at which XLMTM muscles weaken, and their corresponding decrease in gait velocity and stride length. Pulmonary function tests in affected dogs reveal a right-shifted relationship between peak inspiratory flow (PIF) and inspiratory time (TI); neurological assessments indicate that affected puppies as young as 10 weeks show early signs of neurological impairment (neurological severity score, NSS =8.6±0.9) with progressive decline (NSS =5.6±1.7 at 17 weeks-of-age).

CONCLUSIONS

Our findings document the rate of disease progression in a large animal model of XLMTM and lay a foundation for preclinical studies.