Microvascular Dysfunction in Skeletal Muscle Precedes Myocardial Vascular Changes in Diabetic Cardiomyopathy: Sex-Dependent Differences

Sadi Loai; Xuetao Sun; Mansoor Husain; Michael A Laflamme; Herman Yeger; Sara S Nunes; Hai-Ling Margaret Cheng

doi:10.3389/fcvm.2022.886687

Microvascular Dysfunction in Skeletal Muscle Precedes Myocardial Vascular Changes in Diabetic Cardiomyopathy: Sex-Dependent Differences

Front Cardiovasc Med. 2022 May 18:9:886687. doi: 10.3389/fcvm.2022.886687. eCollection 2022.

Authors

Sadi Loai^{1

2}, Xuetao Sun³, Mansoor Husain^{3

4

5}, Michael A Laflamme^{4

6

7}, Herman Yeger^{7

8}, Sara S Nunes^{1

3

7}, Hai-Ling Margaret Cheng^{1

2

9}

Affiliations

¹ Institute of Biomedical Engineering, University of Toronto, Toronto, ON, Canada.
² Translational Biology and Engineering Program, Ted Rogers Centre for Heart Research, Toronto, ON, Canada.
³ Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada.
⁴ Peter Munk Cardiac Centre, University Health Network, Toronto, ON, Canada.
⁵ Ted Rogers Centre for Heart Research, Toronto, ON, Canada.
⁶ McEwen Stem Cell Institute, University Health Network, Toronto, ON, Canada.
⁷ Laboratory of Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada.
⁸ Program in Developmental and Stem Cell Biology, The Hospital for Sick Children, Toronto, ON, Canada.
⁹ The Edward S. Rogers Sr. Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON, Canada.

Abstract

Aim: To uncover sex-related microvascular abnormalities that underlie the early presentation of reduced perfusion in leg skeletal muscle in a type II rat model of diabetic cardiomyopathy.

Methods and results: Diabetes was induced using a non-obese, diet-based, low-dose streptozotocin model in adult female (18 diabetic, 9 control) and male rats (29 diabetic, 11 control). Time-course monitoring over 12 months following diabetes induction was performed using echocardiography, treadmill exercise, photoacoustic imaging, flow-mediated dilation (FMD), histopathology, and immunohistochemistry. Diabetic rats maintained normal weights. Hypertension appeared late in both diabetic males (7 months) and females (10 months), while only diabetic males had elevated cholesterol (7 months). On echocardiography, all diabetic animals maintained normal ejection fraction and exhibited diastolic dysfunction, mild systolic dysfunction, and a slightly enlarged left ventricle. Exercise tolerance declined progressively and early in males (4 months), later in females (8 months); FMD showed lower baseline femoral arterial flow but unchanged reactivity in both sexes (5 months); and photoacoustic imaging showed lower tissue oxygen saturation in the legs of diabetic males (4 months) and diabetic females (10 months). Myocardial perfusion was normal in both sexes. Histopathology at the final timepoint of Month 10 (males) and Month 12 (females) revealed that myocardial microvasculature was normal in both vessel density and structure, thus explaining normal perfusion on imaging. However, leg muscle microvasculature exhibited perivascular smooth muscle thickening around small arterioles in diabetic females and around large arterioles in diabetic males, explaining the depressed readings on photoacoustic and FMD. Histology also confirmed the absence of commonly reported HFpEF markers, including microvessel rarefaction, myocardial fibrosis, and left ventricular hypertrophy.

Conclusion: Exercise intolerance manifesting early in the progression of diabetic cardiomyopathy can be attributed to decreased perfusion to the leg skeletal muscle due to perivascular smooth muscle thickening around small arterioles in females and large arterioles in males. This microvascular abnormality was absent in the myocardium, where perfusion levels remained normal throughout the study. We conclude that although skeletal muscle microvascular dysfunction of the vasculature presents at different levels depending on sex, it consistently presents early in both sexes prior to overt cardiac changes such as rarefaction, fibrosis, or hypertrophy.

Keywords: heart failure; histopathology; microvascular dysfunction; preserved ejection fraction (HFpEF); sex differences; skeletal muscle; type II diabetes.