Adipocyte turnover: relevance to human adipose tissue morphology

Abstract

Objective: Adipose tissue may contain few large adipocytes (hypertrophy) or many small adipocytes (hyperplasia). We investigated factors of putative importance for adipose tissue morphology.

Research design and methods: Subcutaneous adipocyte size and total fat mass were compared in 764 subjects with BMI 18-60 kg/m(2). A morphology value was defined as the difference between the measured adipocyte volume and the expected volume given by a curved-line fit for a given body fat mass and was related to insulin values. In 35 subjects, in vivo adipocyte turnover was measured by exploiting incorporation of atmospheric (14)C into DNA.

Results: Occurrence of hyperplasia (negative morphology value) or hypertrophy (positive morphology value) was independent of sex and body weight but correlated with fasting plasma insulin levels and insulin sensitivity, independent of adipocyte volume (beta-coefficient = 0.3, P < 0.0001). Total adipocyte number and morphology were negatively related (r = -0.66); i.e., the total adipocyte number was greatest in pronounced hyperplasia and smallest in pronounced hypertrophy. The absolute number of new adipocytes generated each year was 70% lower (P < 0.001) in hypertrophy than in hyperplasia, and individual values for adipocyte generation and morphology were strongly related (r = 0.7, P < 0.001). The relative death rate (approximately 10% per year) or mean age of adipocytes (approximately 10 years) was not correlated with morphology.

Conclusions: Adipose tissue morphology correlates with insulin measures and is linked to the total adipocyte number independently of sex and body fat level. Low generation rates of adipocytes associate with adipose tissue hypertrophy, whereas high generation rates associate with adipose hyperplasia.

FIG. 1.

Adipose morphology. A: Curve-linear relationship between fat cell volume and fat mass in all 764 subjects. B: Comparison of curves obtained from fat mass measured with a formula and by bioimpedance in a subset of 555 subjects. C: Distribution of adipose tissue morphology values. D: Frequency of different forms of morphology in male (n = 207), female (n = 557), nonobese (n = 300), and obese (n = 404) subjects. The morphology value is defined in the results section.

FIG. 2.

Relationship between total fat cell number and adipose morphology values (A) or fat cell size (B) in all 764 subjects. The morphology value is defined in the results section.

FIG. 3.

Role of adipocyte turnover for adipose tissue morphology in hypertrophy (n = 12) or hyperplasia (n = 23) subjects. Production rate of new fat cells is shown by groups (A) and in individual subjects (B). The statistical calculation used log-transformed values. Age (C) and death rates (D) of fat cells. The morphology value is defined in the results section.