Circulating Follistatin and Activin A and Their Regulation by Insulin in Obesity and Type 2 Diabetes

BACKGROUND

Circulating follistatin (Fst) binds activin A and thereby regulates biological functions such as muscle growth and β-cell survival. However, Fst and activin A's implication in metabolic regulation is unclear.

OBJECTIVE

To investigate circulating Fst and activin A in obesity and type 2 diabetes (T2D) and determine their association with metabolic parameters. Further, to examine regulation of Fst and activin A by insulin and the influence of obesity and T2D hereon.

METHODS

Plasma Fst and activin A levels were analyzed in obese T2D patients (N = 10) closely matched to glucose-tolerant lean (N = 12) and obese (N = 10) individuals in the fasted state and following a 4-h hyperinsulinemic-euglycemic clamp (40 mU·m-2·min-1) combined with indirect calorimetry.

RESULTS

Circulating Fst was ~30% higher in patients with T2D compared with both lean and obese nondiabetic individuals (P < .001), while plasma activin A was unaltered. In the total cohort, fasting plasma Fst correlated positively with fasting plasma glucose, serum insulin and C-peptide levels, homeostasis model assessment of insulin resistance, and hepatic and adipose tissue insulin resistance after adjusting for age, gender and group (all r > 0.47; P < .05). However, in the individual groups these correlations only achieved significance in patients with T2D (not plasma glucose). Acute hyperinsulinemia at euglycemia reduced circulating Fst by ~30% (P < .001) and this response was intact in patients with T2D. Insulin inhibited FST expression in human hepatocytes after 2 h and even further after 48 h.

CONCLUSIONS

Elevated circulating Fst, but not activin A, is strongly associated with measures of insulin resistance in patients with T2D. However, the ability of insulin to suppress circulating Fst is preserved in T2D.

The first Danish chairs of ophthalmology

In the last century German medical sciences made up the chief inspiration to the medical profession in Europe. The influence of German ophthalmology spread to Denmark, and accordingly the first Danish professor, Edmund Hansen Grut was trained in the Graefe clinic. His successor, Jannik Bjerrum grew up in southern Jutland, a district later on lost to the German Empire. The hitherto prevailing Danish sympathies with the neighbour in the south vanished after this. Bjerrum thus wrote all his papers in Danish and made no efforts to achieve an international reputation. In contrast, Marius Tscherning, received widespread recognition as a scientist. He spent many years in France. His scientific insights at last brought him to the Danish chair of ophthalmology. The history of the first three professors of ophthalmology, so different in their attitudes, has narrative value, but exemplifies as well the rapid development of the profession in the years 1886-1925.