Abstract
BACKGROUND: Type 2 diabetes is commonly characterized by insulin deficiency and decreased sensitivity of insulin receptors, leading to a chronic state of hyperglycemia in individuals. Disease progression induces changes in the immune profile that engenders a chronic inflammatory condition. Thiazolidinedione (TDZ) drugs, such as Pioglitazone (Pio), aid in controlling disease symptoms. While the mechanisms by which Pio controls hyperglycemia are beginning to be understood, relatively little is known about the effects of Pio on suppression of the systemic immune phenotype, attributed to visceral adipose tissue and macrophages. METHODS: Here, we utilize the recently developed BBDZR/Wor type 2 diabetes rat model to test our hypothesis that a selective in vivo growth of CD3(+)T cells in the spleen contributes to the increase in T lymphocytes, including Tregs, independent of visceral adipose tissue. We investigated the systemic effects of Pio on multifactorial aspects of the disease-induced immune phenotype both in vivo and in vitro in normal, non-diabetic animals and in disease. RESULTS: Our work revealed that Pio reversed the lymphopenic status of diabetic rats, in part by an increase in CD3(+) T lymphocytes and related subsets. Moreover, we found evidence that Pio caused a selective growth of newly differentiated T lymphocytes, based on the presence of recent thymic emigrants in vivo. To investigate effects of Pio on the inflammatory milieu, we examined the production of the signature cytokines TNF-α and IL-1β and found they were reduced by Pio-treatment, while the levels of IL-4, an anti-inflammatory mediator, were significantly increased in a Pio-dependent manner. The increase in IL-4 production, although historically attributed to macrophages from visceral adipose tissue under other conditions, came also from CD3(+) T lymphocytes from the spleen, suggesting splenocytes contribute to the Pio-induced shift towards an anti-inflammatory phenotype. CONCLUSIONS: We show for the first time that Pio treatment significantly suppresses the systemic inflammatory status in the BBDZR/Wor type 2 diabetes rat model by the selective growth of newly differentiated CD3(+) T cells and by increasing CD3(+)IL-4 production in immigrant spleen lymphocytes.