Effect of aging on the expression of peroxisome proliferator-activated receptor gamma and the possible relation to insulin resistance

Abstract

Background: The morbidity of insulin resistance tends to increase with aging. However, studies on molecular mechanisms underlying insulin resistance in aging process is still in paucity.

Objective: The effect of aging on peroxisome proliferator-activated receptor gamma (PPARgamma) expression, and in addition, the possible association of PPARgamma expression with insulin resistance in aging process were investigated.

Methods: The minimal model technique (MMT) based on frequently sampled intravenous glucose tolerance test was adopted and SI and glucose effectiveness of young and aged rats were compared. RT-PCR and Western blot were used to determine the expression of PPARgamma at mRNA and protein level in adipose tissue and skeletal muscle, as well as in human colic omentum, respectively.

Results: MMT result implied existence of various degrees of insulin resistance in aged rats. The expression of PPARgamma at both mRNA and protein levels in adipose tissue of aged rats dramatically decreased; consequently, the expression of its target gene lipoprotein lipases mRNA also markedly decreased compared with those in young rats. Furthermore, the level of PPARgamma mRNA and glucose transporter-4 mRNA in skeletal muscle of aged rats attenuated significantly. The expression of PPARgamma mRNA in omental adipose tissue of old men was significantly decreased, accompanied by a tendency of higher insulin resistance index, compared with those of the young.

Conclusion: Aging may be associated with diminished PPARgamma expression affecting insulin resistance in the aged individuals.