Aldose Reductase Regulates Hepatic Peroxisome Proliferator-activated Receptor α Phosphorylation and Activity to Impact Lipid Homeostasis

Abstract

Aldose reductase (AR) is implicated in the development of a number of diabetic complications, but the underlying mechanisms remain to be fully elucidated. We performed this study to determine whether and how AR might influence hepatic peroxisome proliferator-activated receptor ␣ (PPAR␣) activity and lipid metabolism. Our results in mouse hepatocyte AML12 cells show that AR overexpression caused strong suppression of PPAR␣/␦ activity (74%, p < 0.001) together with significant down-regulation of mRNA expression for acetyl-CoA oxidase and carnitine palmitoyltransferase-1. These suppressive effects were attenuated by the selective AR inhibitor zopolrestat. Furthermore, AR overexpression greatly increased the levels of phosphorylated PPAR␣ and ERK1/2. Moreover, AR-induced suppression of PPAR␣ activity was attenuated by treatment with an inhibitor for ERK1/2 but not that for phosphoinositide 3-kinase, p38, or JNK. Importantly, similar effects were observed for cells exposed to 25 mM glucose. In streptozotocindiabetic mice, AR inhibitor treatment or genetic deficiency of AR resulted in significant dephosphorylation of both PPAR␣ and ERK1/2. With the dephosphorylation of PPAR␣, hepatic acetyl-CoA oxidase and apolipoprotein C-III mRNA expression was greatly affected and that was associated with substantial reductions in blood triglyceride and nonesterified fatty acid levels. These data indicate that AR plays an important role in the regulation of hepatic PPAR␣ phosphorylation and activity and lipid homeostasis. A significant portion of the AR-induced modulation is achieved through ERK1/2 signaling.

Cyclin D1 represses peroxisome proliferator-activated receptor alpha and inhibits fatty acid oxidation

“…To examine the potential regulation of PPARα by endogenous cyclin D1, we first utilized the well-differentiated AML12 mouse hepatocyte cell line [29, 30]. Small interfering (si) RNA-mediated knockdown of cyclin D1 efficiently depleted the expression of this protein and inhibited serum-stimulated proliferation of these cells (Figure 2A–2B) [18].…”

Aldose Reductase Is Involved in the Development of Murine Diet-Induced Nonalcoholic Steatohepatitis

“…AML12 cells were plated on 6-well plates at the cell density of approximately 1.0×10 6 /well. On the next day, cells were transfected with pFLAG-mAR, a plasmid constructed as described previously [15] or pFLAG-CMV2 (Sigma) using Lipofectamine 2000 reagent (Invitrogen) according to the manufacturer’s protocol. 36 hours later, cells were collected for mRNA expression analyses.…”

Inhibition of Aldose Reductase Activates Hepatic Peroxisome Proliferator-Activated Receptor-αand Ameliorates Hepatosteatosis in Diabetic db/db Mice

“…RT-PCR was performed to determine the levels of acetyl CoA oxidase ( Aco ), carnitine palmitoyl transferase-1 ( Cpt1 ), apolipoprotein C-III ( ApoC3 ), and apolipoprotein A-V ( ApoA5 ) mRNAs as previously described [17]. The primers used were 5′-CCGCCACCTTCAATCCAGAGTTA-3′ and 5′-TCACAGTTGGGCTGTTGAGAATG-3′ ( Aco ), 5′-GGACGAATCGGAACAGGGATA-3′ and 5′-CCTTGTAATGTGCGAGCTGCA-3′ ( Cpt1 ), 5′-CCTCTTGGCTCTCCTGGCATCT-3′ and 5′-TGCTCCAGTAGCCTTTCAGGG-3′ ( ApoC3 ), 5′-GTGGGAGAAGACAC-CAAG-GCTC-3′ and 5′-GGTCAATGGCCTGAGTAAA-TGC-3′ ( ApoA5 ), 5′-CGAGACCCCACTAA-CATCAAA-3′ and 5′-AGTCTTCTGGGTGGCA-GTGAT-3′ (GAPDH).…”

“…It is known that diabetes, type II diabetes mellitus (T2DM) in particular, is often associated with hepatic accumulation of triglycerides in both rodents and humans, which might eventually lead to the development of hepatic steatosis or nonalcoholic fatty liver disease (NAFLD) [14–16]. Recently, we demonstrated that deficiency or inhibition of AR caused significant dephosphorylation of hepatic PPAR α , leading to the activation of this transcriptional factor as well significant reduction in serum TG levels in streptozotocin-(STZ-) diabetic mice, an experimental model for type I diabetes mellitus (T1DM) [17]. Because T2DM is clinically much predominant than T1DM, in this current study, we wanted to determine whether AR also affects PPAR α in the liver of T2DM db/db mouse models.…”