Cellularity and adipogenic profile of the abdominal subcutaneous adipose tissue from obese adolescents: association with insulin resistance and hepatic steatosis

Abstract

Objective: We explored whether the distribution of adipose cell size, the estimated total number of adipose cells, and the expression of adipogenic genes in subcutaneous adipose tissue are linked to the phenotype of high visceral and low subcutaneous fat depots in obese adolescents.

Research design and methods: A total of 38 adolescents with similar degrees of obesity agreed to have a subcutaneous periumbilical adipose tissue biopsy, in addition to metabolic (oral glucose tolerance test and hyperinsulinemic euglycemic clamp) and imaging studies (MRI, DEXA, (1)H-NMR). Subcutaneous periumbilical adipose cell-size distribution and the estimated total number of subcutaneous adipose cells were obtained from tissue biopsy samples fixed in osmium tetroxide and analyzed by Beckman Coulter Multisizer. The adipogenic capacity was measured by Affymetrix GeneChip and quantitative RT-PCR.

Results: Subjects were divided into two groups: high versus low ratio of visceral to visceral + subcutaneous fat (VAT/[VAT+SAT]). The cell-size distribution curves were significantly different between the high and low VAT/(VAT+SAT) groups, even after adjusting for age, sex, and ethnicity (MANOVA P = 0.035). Surprisingly, the fraction of large adipocytes was significantly lower (P < 0.01) in the group with high VAT/(VAT+SAT), along with the estimated total number of large adipose cells (P < 0.05), while the mean diameter was increased (P < 0.01). From the microarray analyses emerged a lower expression of lipogenesis/adipogenesis markers (sterol regulatory element binding protein-1, acetyl-CoA carboxylase, fatty acid synthase) in the group with high VAT/(VAT+SAT), which was confirmed by RT-PCR.

Conclusions: A reduced lipo-/adipogenic capacity, fraction, and estimated number of large subcutaneous adipocytes may contribute to the abnormal distribution of abdominal fat and hepatic steatosis, as well as to insulin resistance in obese adolescents.

FIG. 1.

Multisizer adipose cell profiles of 20 subjects with a low VAT/(VAT+SAT) ratio (A) and 18 subjects with a high VAT/(VAT+SAT) ratio (B), plotting cell diameter using linear bins against relative frequency in percent C: Cell-size profiles of the adipose cell size using the mean parameters from the curve-fitting formula for subjects with a low VAT/(VAT+SAT) ratio (dashed line) and subjects with a high VAT/(VAT+SAT) ratio (solid line) (P = 0.035 using MANCOVA).

FIG. 2.

Differences in cell-size parameters between the groups with the low (white bar) and the high (black bar) VAT/(VAT+SAT) ratio. (A) nadir, (B) peak diameter (cp), (C) fraction of large cells (fraclarge), (D) number of large cells (means ± SD).

FIG. 3.

Diagram of the insulin signaling pathway from PathVisio. Red colored boxes indicate significantly increased expression, whereas green colored boxes indicate a significantly decreased expression in the high versus low VAT/(VAT+SAT) group. Besides the gene boxes, the P value is given.

FIG. 4.

Box-plots for the expression of SREBF1, FASN, ACACA, LPIN1, ADIPOQ, PPARγ2, and LPL, normalized to the expression of 18S rRNA and based on the expression of a human control adipose tissue (2^ΔΔCt). The white boxes represent the means and SD for the group with the low VAT/(VAT+SAT) ratio, and the black boxes represent the means and SD for the group with the high VAT/(VAT+SAT) ratio. The Mann-Whitney test between the two groups was significant at the <0.05 level (*) or at the <0.005 level (**).

FIG. 5.

Schematic representation of the proposed interactions among size of the subcutaneous fat depot, adipogenesis/lipogenesis, and cell size in the subcutaneous adipose tissue, plasma lipid level, hepatic steatosis, and insulin resistance. (A high-quality digital representation of this figure is available in the online issue.)