Insulin-induced changes in skeletal muscle microvascular perfusion are dependent upon perivascular adipose tissue in women

Abstract

Aims/hypothesis: Obesity increases the risk of cardiovascular disease and type 2 diabetes, partly through reduced insulin-induced microvascular vasodilation, which causes impairment of glucose delivery and uptake. We studied whether perivascular adipose tissue (PVAT) controls insulin-induced vasodilation in human muscle, and whether altered properties of PVAT relate to reduced insulin-induced vasodilation in obesity.

Methods: Insulin-induced microvascular recruitment was measured using contrast enhanced ultrasound (CEU), before and during a hyperinsulinaemic-euglycaemic clamp in 15 lean and 18 obese healthy women (18-55 years). Surgical skeletal muscle biopsies were taken on a separate day to study perivascular adipocyte size in histological slices, as well as to study ex vivo insulin-induced vasoreactivity in microvessels in the absence and presence of PVAT in the pressure myograph. Statistical mediation of the relation between BMI and microvascular recruitment by PVAT was studied in a mediation model.

Results: Obese women showed impaired insulin-induced microvascular recruitment and lower metabolic insulin sensitivity compared with lean women. Microvascular recruitment was a mediator in the association between obesity and insulin sensitivity. Perivascular adipocyte size, determined in skeletal muscle biopsies, was larger in obese than in lean women, and statistically explained the difference in microvascular recruitment between obese and lean women. PVAT from lean women enhanced insulin-induced vasodilation in isolated skeletal muscle resistance arteries, while PVAT from obese women revealed insulin-induced vasoconstriction.

Conclusions/interpretation: PVAT from lean women enhances insulin-induced vasodilation and microvascular recruitment whereas PVAT from obese women does not. PVAT adipocyte size partly explains the difference in insulin-induced microvascular recruitment between lean and obese women.

Fig. 1

Outline of the hyperinsulinaemic–euglycaemic clamp and microvascular recruitment study day

Fig. 2

The difference in insulin-induced microvascular recruitment between lean and obese women, and the contribution thereof to metabolic insulin sensitivity. (a) Changes in MBV in lean and obese women. Lean women show insulin-induced microvascular recruitment (27% [−19 to +99], *p < 0.05). In the obese women, insulin did not significantly recruit additional MBV (9% [−37 to +32], p = 0.97). When these data were log-transformed and tested parametrically (unpaired t test), the difference in microvascular recruitment was significantly different between lean and obese women, *p < 0.05. (b) Indirect effects of microvascular recruitment on metabolic insulin sensitivity (M value). BMI group was related with M value with a β coefficient of −0.39, p < 0.05, corrected for age (horizontal path, between brackets). The β coefficient for the BMI group to microvascular recruitment was −0.40, p < 0.05 (upsloping path), and the β coefficient for microvascular recruitment to M value 0.50, p < 0.01 (downsloping path). Mediation analysis confirmed the mediating role of microvascular recruitment in the relation between the BMI group and M value (β = −0.37, CI [−1.09, −0.08]). Indeed, the β coefficient from the BMI group to M value was attenuated to −0.21, p = 0.23 (horizontal path, number outside brackets). *p < 0.05, **p < 0.01. See ESM Table 1 for CIs of the unadjusted and adjusted β coefficients from the BMI group to M value

Fig. 3

Perivascular adipocyte size partly explains the difference in microvascular recruitment between lean and obese women. (a) Typical example of a haematoxylin and eosin staining with an arteriole and microvascular muscle PVAT. Black arrow, resistance artery; yellow arrow, PVAT; red arrow, skeletal muscle. Scale bar ≈ 100 μm. (b) In lean women, the size of individual adipocytes in PVAT was smaller than in obese women (530 [407–832] vs 1,637 [679–2,518], p < 0.01 [Mann–Whitney U test]). (c) Indirect effects of perivascular adipocyte size on insulin-induced microvascular recruitment. The BMI group was related to insulin-induced microvascular recruitment with a β coefficient of −0.40, p < 0.05, corrected for age (horizontal path, between brackets). The β coefficient for the BMI group to PVAT adipocyte size was 1.08, p < 0.05 (upsloping path) and the β coefficient for PVAT adipocyte size to insulin-induced microvascular recruitment −0.40, p = 0.065 (downsloping path). Mediation analysis confirmed the mediating role of PVAT adipocyte size in the relation between the BMI group and insulin-induced microvascular recruitment (β = −0.29, CI [−0.96 to −0.01]). Indeed, the β coefficient from the BMI group to microvascular recruitment was attenuated to 0.01, and no longer significant (horizontal path, number outside brackets), showing that perivascular adipocyte size is a significant mediator in the relationship between the BMI group and microvascular recruitment. **p < 0.01. See ESM Table 2 for CIs of the unadjusted and adjusted β coefficients from BMI group to microvascular recruitment

Fig. 4

PVAT regulates insulin-induced vasoreactivity ex vivo. (a) Example of a cannulated microvessel free from PVAT. Scale bar ≈ 100 μm. (b) Without PVAT, microvessels from both lean (triangles, n = 6) and obese women (squares, n = 8) do not exhibit changes in vascular diameter to increasing doses of insulin in the pressure myograph; but PVAT from lean women (circles, n = 8) potentiates insulin-induced vasodilation at the highest concentration, whereas PVAT from obese women (diamonds, n = 8) enhances insulin-induced vasoconstriction. *p < 0.05 obese microvessel, no PVAT vs obese microvessel + PVAT; ^† p < 0.05 obese microvessel + PVAT vs lean microvessel + PVAT; ^††† p < 0.001 obese microvessel + PVAT vs lean microvessel + PVAT; ^‡ p < 0.05 lean microvessel, no PVAT vs lean microvessel + PVAT