Glucose homeostasis is maintained by the orchestration of peripheral glucose utilization and hepatic glucose production, mainly by insulin. In this study, we found by utilizing a combined parallel chromatography mass profiling approach that lysophosphatidylcholine (LPC) regulates glucose levels. LPC was found to stimulate glucose uptake in 3T3-L1 adipocytes dose-and time-dependently, and this activity was found to be sensitive to variations in acyl chain lengths and to polar head group types in LPC. Treatment with LPC resulted in a significant increase in the level of GLUT4 at the plasma membranes of 3T3-L1 adipocytes. Moreover, LPC did not affect IRS-1 and AKT2 phosphorylations, and LPC-induced glucose uptake was not influenced by pretreatment with the PI 3-kinase inhibitor LY294002. However, glucose uptake stimulation by LPC was abrogated both by rottlerin (a protein kinase C␦ inhibitor) and by the adenoviral expression of dominant negative protein kinase C␦. In line with its determined cellular functions, LPC was found to lower blood glucose levels in normal mice. Furthermore, LPC improved blood glucose levels in mouse models of type 1 and 2 diabetes. These results suggest that an understanding of the mode of action of LPC may provide a new perspective of glucose homeostasis.

Impaired revascularization of transplanted islets is a critical problem that leads to progressive islet loss. Since endothelial progenitor cells (EPCs) are known to aid neovascularization, we aimed to enhance islet engraftment by cotransplanting EPCs with islets. Porcine islets, with (islet-EPC group) or without (islet-only group) human cord blood–derived EPCs, were transplanted into diabetic nude mice. The islet-EPC group reached euglycemia by ∼11 days posttransplantation, whereas the islet-only group did not. Also, the islet-EPC group had a higher serum porcine insulin level than the islet-only group. Islets from the islet-EPC group were more rapidly revascularized at the early period of transplantation without increment of final capillary density at the fully revascularized graft. Enhanced revascularization rate in the islet-EPC group was mainly attributed to stimulating vascular endothelial growth factor-A production from the graft. The rapid revascularization by EPC cotransplantation led to better graft perfusion and recovery from hypoxia. EPC cotransplantation was also associated with greater β-cell proliferation, probably by more basement membrane production and hepatocyte growth factor secretion. In conclusion, cotransplantation of EPCs and islets induces better islet engraftment by enhancing the rate of graft revascularization. These findings might provide a directly applicable tool to enhance the efficacy of islet transplantation in clinical practice.

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Here, we demonstrate that SENP2, a desumoylating enzyme, plays a critical role in the control of adipogenesis. SENP2 expression was markedly increased upon the induction of adipocyte differentiation, and this increase was dependent on protein kinase A activation. Remarkably, knockdown of SENP2 led to a dramatic attenuation of adipogenesis with a marked decrease in PPAR␥ and C/EBP␣ mRNA levels. Knockdown of SENP2 also caused a marked reduction in the level of C/EBP␤ protein but not in that of C/EBP␤ mRNA. Interestingly, sumoylation of C/EBP␤ dramatically increased its ubiquitination and destabilization, and this increase could be reversed by SENP2. In addition, overexpression of C/EBP␤ could overcome the inhibitory effect of SENP2 knockdown on adipogenesis. Furthermore, SENP2 was absolutely required for adipogenesis of preadipocytes implanted into mice. These results establish a critical role for SENP2 in the regulation of adipogenesis by desumoylation and stabilization of C/EBP␤ and in turn by promoting the expression of its downstream effectors, such as PPAR␥ and C/EBP␣.A large number of transcription factors are modified by the small ubiquitin (Ub)-related modifier (SUMO), and this covalent modification regulates their transcriptional activities (12,16,17). Unlike ubiquitination, SUMO modification is not a signal for protein degradation. SUMO modification regulates the target proteins through various mechanisms such as affecting cellular localization, protein-protein interaction, or stability of the target proteins. SUMO modification (sumoylation) is a reversible process that is catalyzed by SUMO-specific proteases (SENPs) (27). Six SENPs (SENP1, -2, -3, -5, -6, and -7) have been identified in humans, and they have different cellular localization and substrate specificities (42). Although the biochemical properties of SENPs have been well documented, their specific targets and physiological roles are known in a limited number of cases. SENP1 plays a key role in the hypoxic response by regulating HIF1␣ stability (6). SUSP4, a newly identified mouse SENP, inhibits cell growth by positively regulating p53 by promoting the self-ubiquitination of Mdm2 (21). In addition, overexpression of SENP2 is involved in the downregulation of ␤-catenin, whereas the direct target of SENP2 in this process is unknown (19). It has also been reported that SENP5 regulates cell division and mitochondrial morphology; however, the targets of SENP5 have not been identified (9, 46).The adipose tissues function as a reservoir of excessive energy. They also secrete adipokines that regulate physiological and pathological events involving energy metabolism, insulin sensitivity, atherogenesis, and inflammatory responses. Adipocyte differentiation from preadipocytes occurs by serial inductions of transcription factors, and this process is tightly regulated. Expression of C/EBP␤ and C/EBP␦ is induced immediately after stimulation, followed by the induction of PPAR␥ and C/EBP␣ (5, 43). PPAR␥ induces several adipocyte-specific genes, including aP2...

Objective-There is still debate as to whether antiatherosclerotic effect of PPAR␥ ligands is dependant on PPAR␥ gene itself or some other pathway. Methods and Results-To investigate the effect of PPAR␥ gene modulation on neointima formation after balloon injury, we delivered adenoviral vectors expressing the wild-type (WT) dominant negative (DN) PPAR␥, or a control gene (␤-galactosidase [BG]) into carotid artery after balloon injury in rosiglitazone (a PPAR␥ ligand)-treated (Rϩ) (3 mg/kg/d) and nontreated (RϪ) rats. Two weeks after gene delivery, in both Rϩ and RϪ animals, the PPAR␥-WT gene transfer showed a significantly lower intima-media ratio (IMR) than control group. Moreover, the delivery of a PPAR␥-DN form showed the highest IMR (in RϩWT, 0.51Ϯ0.15; RϩBG, 0.89Ϯ0.14; RϩDN, 1.20Ϯ0.18, PϽ0.05 and in RϪWT, 0.91Ϯ0.21; RϪBG, 1.44Ϯ0.23; RϪDN, 1.74Ϯ0.29, PϽ0.05). Proliferation and migration showed same result pattern as IMR. In addition, apoptotic indices were significantly higher in the PPAR␥-WT gene transferred group than in the PPAR␥-DN group. Conclusions-In vivo transfer of the PPAR␥-WT gene was found to inhibit smooth muscle proliferation, sustain apoptosis, and reduce neointima formation after balloon injury irrespective of rosiglitazone treatment. These results indicate that PPAR␥ overexpression itself has a protective role against restenosis after balloon injury. Key Words: PPAR␥ Ⅲ vascular smooth muscle Ⅲ neointima Ⅲ proliferation Ⅲ apoptosis P eroxisome proliferator activated receptor gamma (PPAR␥) is a crucial factor in many cellular signaling pathways and is known to regulate several transcription factors. Researches have provided many insights into the pleiotropic role that PPAR␥ plays in cell proliferation, migration, and differentiation and adipocyte differentiation. In fact, PPAR␥ activation inhibits vascular smooth muscle cell (VSMC) proliferation, 1,2 for which several mechanisms have been suggested; blocking the reentry of quiescent VSMCs into the cell cycle, 3 inhibiting VSMC migration by controlling the mitogen-activated protein kinase (MAPK) pathway and the production of matrix metalloproteinase (MMP), 4,5 and reducing inflammation by attenuating cytokine production and nuclear factor-B transcription activity. 6,7 In the field of endocrinology and metabolism, PPAR␥ has been identified as an insulin sensitizer and as an important regulator of glucose metabolism. In fact, the diabetic milieu is associated with endothelial dysfunction and several therapeutic interventions have been tested in this context. 8 Moreover, PPAR␥ is a good target for the treatment of restenosis because its expression is found in all cells composing blood vessels (ie, monocytes, macrophages, and endothelial and VSMCs).It has recently been reported that the in vitro rosiglitazone treatment (a PPAR␥ ligand) results in a significant reduction in restenosis after coronary stent insertion. 9 Because PPAR␥ is located at a nodal point where multiple cell signals merge to control the proliferation and migration of VSMCs, it ma...