Adipocyte Turnover: Relevance to Human Adipose Tissue Morphology

TLDR

Adipose tissue can exhibit either few large adipocytes (hypertrophy) or many small adipocytes (hyperplasia). The study aimed to identify factors that influence adipose tissue morphology. Researchers compared subcutaneous adipocyte size and total fat mass in 764 adults (BMI 18–60 kg/m²), defined a morphology value as the deviation of measured adipocyte volume from the expected volume for a given body fat mass and related it to insulin measures, and measured in vivo adipocyte turnover in 35 subjects using atmospheric ¹⁴C incorporation into DNA. Morphology was independent of sex and weight but positively associated with fasting insulin and insulin sensitivity; total adipocyte number was inversely related to morphology, with hypertrophy showing a 70 % lower annual adipocyte generation rate than hyperplasia, while adipocyte death rates and mean ages were similar across morphologies.

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/m2. 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 14C 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 (β-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 (∼10% per year) or mean age of adipocytes (∼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.