Roles of 12-Lipoxygenase and Its Interaction with Angiotensin II on p21 and p27 Expression in Diabetic Nephropathy

Abstract

Background: 12-Lipoxygenase (12-LO) and angiotensin II (Ang II) are involved in the development of diabetic renal hypertrophy, in which cyclin-kinase inhibitors, p21 and p27 play pivotal roles. Here, we study the effects of 12-LO and its interaction with Ang II on glomerular p21 and p27 expression in diabetic conditions. Methods: Models used in the current study include glomerular mesangial cells (MCs); and glomeruli from (1) type 2 diabetic db/db mice; (2) type 2 diabetic rats induced by high-fat diet feeding followed by streptozotocin injection; (3) 12-LO knockout (12-LOKO) mice; and (4) normal rats infused with Ang II or 12(S)-hydroxyeicosatetraenoic acid (12[S]-HETE, arachidonic acid metabolite of 12-LO). Results: The protein expression levels of p21 and p27 were increased in high glucose-stimulated MCs and in glomeruli isolated from db/db mice. In type 2 diabetic rats, cinnamyl-3,4-dihydroxy-α-cynanocinnamate (inhibitor of 12-LO) attenuated the increases in glomerular p21 and p27 protein expression, while in normal rats, 12(S)-HETE injection increased glomerular p21 and p27 expression. 12(S)-HETE and Ang II were mutually stimulated in glomeruli. Glomerular p21 and p27 expression were decreased in 12-LOKO mice compared to levels in control mice, and Ang II stimulation increased the protein expression of p27 in control but not 12-LOKO mice. Ang II stimulation had no effect on p21 protein expression in 12-LOKO mice. Conclusion: 12-LO is involved in diabetic renal hypertrophy via the induction of p21 and p27 protein expression and interacts with Ang II to induce p27 upregulation in diabetes. The current results suggest a potential amplifying loop in the pathogenesis of diabetic nephropathy.