Involvement of Inducible 6-Phosphofructo-2-kinase in the Anti-diabetic Effect of Peroxisome Proliferator-activated Receptor γ Activation in Mice

Abstract

PFKFB3 is the gene that codes for the inducible isoform of 6-phosphofructo-2-kinase (iPFK2), a key regulatory enzyme of glycolysis. As one of the targets of peroxisome proliferatoractivated receptor ␥ (PPAR␥), PFKFB3/iPFK2 is up-regulated by thiazolidinediones. In the present study, using PFKFB3/iPFK2-disrupted mice, the role of PFKFB3/iPFK2 in the anti-diabetic effect of PPAR␥ activation was determined. In wild-type littermate mice, PPAR␥ activation (i.e. treatment with rosiglitazone) restored euglycemia and reversed high fat diet-induced insulin resistance and glucose intolerance. In contrast, PPAR␥ activation did not reduce high fat diet-induced hyperglycemia and failed to reverse insulin resistance and glucose intolerance in PFKFB3 ؉/؊ mice. The lack of anti-diabetic effect in PFKFB3 ؉/؊ mice was associated with the inability of PPAR␥ activation to suppress adipose tissue lipolysis and proinflammatory cytokine production, stimulate visceral fat accumulation, enhance adipose tissue insulin signaling, and appropriately regulate adipokine expression. Similarly, in cultured 3T3-L1 adipocytes, knockdown of PFKFB3/iPFK2 lessened the effect of PPAR␥ activation on stimulating lipid accumulation. Furthermore, PPAR␥ activation did not suppress inflammatory signaling in PFKFB3/iPFK2-knockdown adipocytes as it did in control adipocytes. Upon inhibition of excessive fatty acid oxidation in PFKFB3/iPFK2-knockdown adipocytes, PPAR␥ activation was able to significantly reverse inflammatory signaling and proinflammatory cytokine expression and restore insulin signaling. Together, these data demonstrate that PFKFB3/iPFK2 is critically involved in the anti-diabetic effect of PPAR␥ activation.

Targeted Overexpression of Inducible 6-Phosphofructo-2-kinase in Adipose Tissue Increases Fat Deposition but Protects against Diet-induced Insulin Resistance and Inflammatory Responses

“…All mice were maintained on a 12:12-h light/dark cycle (lights on at 06:00). At 5-6 weeks of age, male mice were fed an HFD (60% fat calories, 20% protein calories, and 20 carbohydrate calories) or a low fat diet (LFD) (10% fat calories, 20% protein calories, and 70 carbohydrate calories) for 12 weeks as described previously (20,21). After the feeding regimen, mice were fasted for 4 h before sacrifice for collection of blood and tissue samples (24 -26).…”

“…Histological and Immunohistochemical Analyses-The paraffin-embedded adipose tissue and liver blocks were cut into sections of 5 m thickness and stained with H&E. In addition, sections were stained for the expression of cell (macrophage) surface marker (F4/80) with rabbit anti-F4/80 (1:100) (AbD Serotec, Raleigh, NC) as described previously (20,21). The frac-tion of F4/80-expressing cells for each sample was calculated as the sum of the number of nuclei of F4/80-expressing cells divided by the total number of nuclei in sections of each sample.…”

“…For insulin tolerance tests, blood samples (5 l) were collected from the tail vein before and at 15,30,45, and 60 min after the bolus insulin injection. Similarly, for glucose tolerance tests, blood samples were collected from the tail vein before and at 30, 60, 90, and 120 min after the glucose bolus injection (20,21).…”

“…The amount of iPFK2 in white adipose tissue, liver, muscle, and bone marrow samples was determined using Western blot analyses (20,21).…”

“…Recent evidence demonstrates that global disruption of PFKFB3/iPFK2 blunts diet-induced adiposity but exacerbates adipose tissue inflammatory response and systemic insulin resistance (20). Additionally, PFKFB3/iPFK2 is involved in the anti-inflammatory and anti-diabetic effects of PPAR␥ activation likely by promoting fat synthesis in adipose tissue (21). At the cellular level, PFKFB3/iPFK2 increases adipocyte glycolysis and glycolysis-driven lipogenesis.…”