Collagen and reticular fibers in left ventricular muscle in diabetic rats: Physical exercise prevents its changes?

Dynamic evolution and mechanism of myocardial glucose metabolism in different functional phenotypes of diabetic cardiomyopathy - a study based on 18 F-FDG microPET myocardial metabolic imaging

PURPOSE

To use ¹⁸ F-FDG microPET dynamic imaging to preliminarily identify the changes of myocardial glucose metabolism corresponding to different functional phenotypes of diabetic cardiomyopathy (DCM) in mice and elucidate their relationships.

METHODS

Left ventricular function was measured by echocardiography in C57BL/KsJ-db/db (db/db) mice and their controls at 8, 12, 16, and 20 weeks of age to divide DCM stages and functional phenotypes. Myocardial histopathology was used to verify the staging accuracy and list-mode microPET dynamic imaging was conducted. The myocardial metabolic rate of glucose (MRglu) and the glucose uptake rate constant (Ki) were derived via Patlak graphical analysis, and the differences in myocardial glucose metabolism levels in different DCM stages were compared. The key proteins involved in myocardial glucose metabolism signaling pathway were analyzed by Western blotting to elucidate the underlying mechanism of abnormal glucose metabolism in DCM.

RESULTS

Compared with the controls, the ratio of early diastolic transmitral flow velocity to early diastolic mitral annular tissue velocity (E/e') of db/db mice was significantly increased from the age of 12 weeks, while the left ventricular ejection fraction (LVEF) was significantly decreased from the age of 16 weeks (all P < 0.05). Based on the staging criteria, 8 and 12 weeks (8/12w) db/db mice were in DCM stage 1 (diastolic dysfunction with normal LVEF), and 16 and 20 weeks (16/20w) db/db mice were in DCM stage 2/3 (diastolic and systolic dysfunction). The degree of myocardial fibrosis, glycogen deposition and ultrastructural damage in 16/20w db/db mice were more obvious than those in 8/12w group. The myocardial MRglu, Ki of db/db mice in 8/12w group or 16/20w group were significantly lower than those in the control group (all P < 0.05), while the myocardial standard uptake value (SUV) was not significantly reduced in the 8/12w group compared with the control group (P > 0.05). MRglu and SUV were moderately negatively correlated with the E/e' ratio (r=-0.539 and - 0.512, P = 0.007 and 0.011), which were not significantly correlated with LVEF (P > 0.05). Meanwhile, Ki was not significantly correlated with LVEF or E/e' ratio. The decreased expression of glucose transporter (GLUT) -4 in db/db mice preceded GLUT-1 and was accompanied by decreased phosphorylated AMP-activated protein kinase (p-AMPK) expression. Myocardial MRglu, Ki and SUV were significantly positively correlated with the expression of GLUT-4 (MRglu: r = 0.537; Ki: r = 0.818; SUV: r = 0.491; P = 0.000 ~ 0.046), but there was no significant correlation with GLUT-1 expression (P = 0.238 ~ 0.780).

CONCLUSIONS

During the progression of DCM, with the changes of left ventricular functional phenotype, abnormal and dynamic changes of myocardial glucose metabolism can occur in the early stage.

Independent and combined effects of liraglutide and aerobic interval training on glycemic control and cardiac protection in diabetic cardiomyopathy rats

OBJECTIVE

This study intended to explore the hypoglycemic and cardioprotective effects of 8-week aerobic interval training combined with liraglutide and elucidate the underlying mechanisms.

METHOD

Male Wistar rats were randomly divided into 5 groups - normal control group (CON), diabetic cardiomyopathy group (DCM), high-dose liraglutide group (DH), low-dose liraglutide group (DL), and aerobic interval training combined with liraglutide group (DLE). High-fat diet and streptozotocin (STZ) were used to induce the DCM model, and both the liraglutide administration group and combination therapy group allocated to 8 weeks of either liraglutide or liraglutide and exercise intervention. Cardiac functions were analyzed by electrocardiography. Blood biochemical parameters were measured to judge glycemic control conditions. Hematoxylin and eosin (HE) staining and Sirus red staining was used to identify cardiac morphology and collagen accumulation, respectively. Advanced glycation end products (AGEs) were determined by enzymatic methods. The mRNA expression of myocardial remodeling genes (BNP, GSK3β, α-MHC, β-MHC and PPARα) and the protein expression of GLP-1, GLP-1R were analyzed.

RESULTS

DCM rats developed hyperglycemia, impaired cardiac function with accumulation of AGEs and collagen (P < 0.05). The development of hyperglycemia and cardiac dysfunction was significantly attenuated with all interventions, as reduced cardiac fibrosis and improved cardiac function (P < 0.05). Cardiac remodeling genes were normalized after all interventions, these positive modifications were due to increased GLP-1 and GLP-1R expression in DCM heart (P < 0.05). Liraglutide combined with AIT significantly increased the diameters of cardiomyocytes, increased the α-MHC expressionx, reduced PPARαexpression and reduced the fluctuation of blood glucose level, which showed the safety and effective of medicine combined with exercise.

CONCLUSION

Liraglutide combined with AIT intervention normalized blood glucose alleviates myocardial fibrosis and improves cardiac contractile function in DCM rats, supporting the efficacy and safety of the combination therapy.

The effects of exercise training on cardiac matrix metalloproteinases activity and cardiac function in mice with diabetic cardiomyopathy

AIM

To evaluate the effects of exercise training (ET) on cardiac extracellular matrix (ECM) proteins homeostasis and cardiac dysfunction in mice with diabetic cardiomyopathy.

METHODS

Thirty-six male C57BL/6 mice were randomized into 3 groups for 8 weeks (12mice/group): Diabetic control-DC: Diabetes was induced by single streptozotocin injection (200 mg/kg i.p.); Diabetic exercise-DE: Diabetic mice underwent ET program on motorized-treadmill (6-times/week, 60min/session); Non-diabetic control-NDC: Vehicle-treated, sedentary, non-diabetic mice served as controls. Before euthanasia, all groups underwent transthoracic echocardiography (TTE). Post-mortem, left-ventricle (LV) samples were histologically analysed for ECM proteins (collagen, elastin), matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs).

RESULTS

DC group showed significantly higher cardiac contents of collagen and MMP-9 and lower elastic concentration than NDC (p < 0.001). The implementation of ET completely outweighed those diabetes-induced changes (DE vs NDC, p > 0.05). TIMP-1 levels significantly increased across all groups (DC: 18.98 ± 3.47%, DE: 24.24 ± 2.36%, NDC: 46.36 ± 5.91%; p < 0.05), while MMP-9/TIMP-1 ratio followed a reverse pattern. ET tended to increase MMP-2 concentrations versus DC (p = 0.055), but did not achieve non-diabetic levels (p < 0.05). TIMP-2 cardiac concentrations remained unaltered throughout the study (p > 0.05). Importantly, ET ameliorated both LV end-systolic internal diameter (LVESD) (p < 0.001) and the percentage of LV fractional shortening (FS%) (p = 0.006) compared to DC. Despite that favorable effect, the cardiac function level of DE group remained worse than NDC group (%FS: p = 0.002; LVESD: p < 0.001).

CONCLUSION

Systemic ET may favorably change ECM proteins, MMP-9 and TIMP-1 cardiac concentrations in mice with diabetic cardiomyopathy. Those results were associated with partial improvement of echocardiography-assessed cardiac function, indicating a therapeutic effect of ET in diabetic cardiomyopathy.

Cardiac hypertrophy associated with myeloproliferative neoplasms in JAK2V617F transgenic mice

BACKGROUND

Myeloproliferative neoplasms (MPNs) are blood malignancies manifested in increased production of red blood cells, white blood cells, and/or platelets. A major molecular lesion associated with the diseases is JAK2V617F, an activation mutation form of tyrosine kinase JAK2. Cardiovascular events represent the leading cause of morbidity and mortality associated MPNs, but the underlying mechanism is not well understood.

METHODS

Previously, we generated JAK2V617F transgenic mice which displayed MPN-like phenotypes. In the present study, we further characterized these mice by analyzing the time course of MPN phenotype development and associated cardiac abnormalities. We performed detailed histochemical staining of cardiac sections.

RESULTS

JAK2V617F transgenic mice developed cardiomegaly as a subsequent event of increased blood cell production during the course of MPN phenotype development. The cardiomegaly is manifested in increased ventricular wall thickness and enlarged cardiomyocytes. Trichrome and reticulin staining revealed extensive collagen fibrosis in the heart of JAK2V617F transgenic mice. Thrombosis in the coronary artery and inflammatory cell infiltration into cardiac muscle were also observed in JAK2V617F transgenic mice, and the latter event was accompanied by fibrosis.

CONCLUSION

JAK2V617F-induced blood disorders have a major impact on heart function and lead to cardiac hypertrophy. JAK2V617F transgenic mice represent an excellent model system to study both hematological malignancies and cardiovascular diseases.