GLUT4 protein expression in obese and lean 12-month-old rats: insights from different types of data analysis

GLUT4 protein expression in white adipose tissue (WAT) and skeletal muscle (SM) was investigated in 2-month-old, 12-month-old spontaneously obese or 1 2-month-old calorie-restricted lean Wistar rats, by considering different p arameters of analysis, such as tissue and body weight, and total protein yi eld of the tissue. In WAT, a similar to 70% decrease was observed in plasma membrane and microsomal GLUT4 protein, expressed as pg protein or g tissue , in both 12-month-old obese and 12-month-old lean rats compared to 2-month -old rats. However, when plasma membrane and microsomal GLUT4 tissue conten ts were expressed as g body weight, they were the same. In SM, GLUT4 protei n content, expressed as pg protein, was similar in 2-month-old and 12-month -old obese rats, whereas it was reduced in 12-month-old obese rats, when ex pressed as g tissue or g body weight, which may play an important role in i nsulin resistance. Weight loss did not change the SM GLUT4 content. These r esults show that altered insulin sensitivity is accompanied by modulation o f GLUT4 protein expression. However, the true role of WAT and SM GLUT4 cont ents in whole-body or tissue insulin sensitivity should be determined consi dering not only GLUT4 protein expression, but also the strong morphostructu ral changes in these tissues, which require different types of data analysi s.