FC028: Characterization of Adipocyte Size and Glucose Uptake in Adipose Tissue with Focus on Different Perirenal Fat Depots

Abstract

Abstract BACKGROUND AND AIMS Previous studies have suggested that the anatomical location of adipose tissue, and the characteristics of the adipocytes regulating adipose tissue function may be of importance for normal renal function and disease. However, in humans, the adipocyte size and metabolism of the fat depots surrounding the kidney have not been thoroughly characterized. The aim of this study was therefore to characterize adipocyte size and glucose uptake in human perirenal, renal sinus and paranephric adipose tissue. SUBJECTS AND METHODS A total of 25 healthy kidney donors [13 (50%) men, age 48 ± 11 years and BMI 25.7 ± 3.1 kg/m2] were included. Perirenal, renal sinus, paranephric, omental and subcutaneous adipose tissue were collected during laparoscopic unilateral nephrectomy. Adipocyte diameter, basal glucose uptake (no insulin) and insulin-stimulated glucose uptake (25 and 1000 µU/mL) were measured in isolated adipocytes from the different tissues. RESULTS The mean adipocyte cell diameters in the renal fat depots (perirenal, renal sinus and paranephric) were smaller than those in omental and subcutaneous tissue (mean ± sd; 69.3 ± 15.5, 65.5 ± 13.5 and 75.9 ± 16.5 versus 80.3 ± 20.5 and 85.5 ± 16.7 µm, respectively) with adipocytes from the renal sinus fat depot having the smallest cell diameter. Detailed data are displayed in Fig. 1. There were no significant gender differences in cell size and adipocyte size from the different depots did not correlate with body mass index (BMI). Insulin resistance index (HOMA-IR) correlated positively and significantly to adipocyte size in the omental (r = 0.607; P = 0.008), perirenal (r = 0.443; P = 0.027) and paranephric (r = 0.479; P = 0.015) depots. Insulin (both with 25 and 1000 µU/mL) significantly up-regulated glucose uptake in subcutaneous (1.6 and 1.9-fold; P < 0.05), perirenal (1.7 and 2.0-fold; P < 0.01) and paranephric (1.5 and 1.6-folds; P < 0.01) adipocytes, compared with basal (no insulin) as shown in Fig. 2. Interestingly, glucose uptake per cell surface was higher in renal sinus than omental adipocytes (basal (no insulin) 1.2-fold; P < 0.001, physiological (25 µU/mL) and supraphysiological (1000 µU/mL) both 1.3-fold higher; P < 0.001) than omental adipocytes (comparison not shown). CONCLUSION This study in healthy kidney donors indicate differences in different fat depots surrounding the kidney that may be of importance for renal function and disease. The fat depot in the renal sinus, with the smallest adipocytes and potentially a higher glucose uptake, is of specific interest. Detailed metabolic characterization of these fat depots is ongoing. Comparison of adipocyte diameter between the different adipose tissue depots: subcutaneous (n = 24), omental (n = 18), perirenal (n = 25), renal sinus (n = 21) and paranephric adipose tissue (n = 25); Values are mean with SEM as data were normally distributed. **P < 0.01 and ***P < 0.001. Physiological and supraphysiological effect of insulin (25 and 1000 µU/mL) on glucose uptake compared with basal (no insulin) by cell surface in adipocytes isolated from subcutaneous (n = 6), omental (n = 3), perirenal (n = 21), renal sinus (n = 4) and paranephric (n = 18) adipose tissue depots, respectively. Values are median and interquartile range as data were not normally distributed. *P < 0.05, **P < 0.01.