Chongmin Huan

Effect of myriocin on plasma sphingolipid metabolism and atherosclerosis in apoE-deficient mice.

Sphingolipids play a very important role in cell membrane formation, signal transduction, and plasma lipoprotein metabolism, all of which may well have an impact on the development of atherosclerosis. To investigate the relationship between sphingolipid metabolism and atherosclerosis, we utilized myriocin to inhibit mouse serine palmitoyl-CoA transferase (SPT), the key enzyme for sphingolipid biosynthesis. We injected 8-week-old apoE-deficient mice with myriocin (0.3 mg/kg/every other day, intraperitoneal) for 60 days. On a chow diet, myriocin treatment caused a significant decrease (50%) in liver SPT activity (p < 0.001), significant decreases in plasma sphingomyelin, ceramide, and sphingosine-1-phosphate levels (54, 32, and 73%, respectively) (p < 0.0001), and a significant increase in plasma phosphatidylcholine levels (91%) (p < 0.0001). Plasma total cholesterol and triglyceride levels demonstrated no significant changes, but there was a significant decrease in atherosclerotic lesion area (42% in root and 36% in en face assays) (p < 0.01). On a high fat diet, myriocin treatment caused marked decreases in plasma sphingomyelin, ceramide, and sphingosine-1-phosphate levels (59, 66, and 81%, respectively) (p < 0.0001), and a marked increase in plasma phosphatidylcholine levels (100%) (p < 0.0001). Total cholesterol and triglyceride demonstrated no significant changes, but there was a significant decrease in atherosclerotic lesion area (39% in root and 37% in en face assays) (p < 0.01). These results indicate that, apart from cholesterol levels, sphingolipids have an effect on atherosclerotic development and that SPT has proatherogenic properties. Thus, inhibition of SPT activity could be an alternative treatment for atherosclerosis.

Macrophage Sphingomyelin Synthase 2 Deficiency Decreases Atherosclerosis in Mice

Rationale: Sphingomyelin synthase (SMS)2 contributes to de novo sphingomyelin (SM) biosynthesis and plasma membrane SM levels. SMS2 deficiency in macrophages diminishes nuclear factor &kgr;B and mitogen-activated protein kinase activation induced by inflammatory stimuli. Objective: The effects of SMS2 deficiency on the development of atherosclerosis are investigated. Methods and Results: We measured cholesterol efflux from macrophages of wild-type (WT) and SMS2 knockout (KO) mice. We transplanted SMS2 KO mouse bone marrow into low-density lipoprotein (LDL) receptor (LDLr) knockout mice (SMS2−/−→LDLr−/−), creating a mouse model of SMS2 deficiency in the macrophages. We found that SMS2 deficiency caused significant induction of cholesterol efflux in vitro and in vivo. Moreover, we found that SMS2 KO mice had less interleukin-6 and tumor necrosis factor α in the circulation before and after endotoxin stimulation, compared with controls. More importantly, after 3 months on a western-type diet, SMS2−/−→LDLr−/− mice showed decreased atherosclerotic lesions in the aortic arch, root (57%, P<0.001), and the entire aorta (42%, P<0.01), compared with WT→LDLr−/− mice. Analysis of plaque morphology revealed that SMS2−/−→LDLr−/− mice had significantly less necrotic core area (71%, P<0.001), less macrophage content (37%, P<0.01), and more collagen content (35%, P<0.05) in atherosclerotic lesions. We also found that SMS2−/−→LDLr−/− mice had significantly lower free cholesterol and cholesteryl ester levels in the brachiocephalic artery than WT→LDLr−/− mice (33 and 52%, P<0.01 and P<0.001, respectively). Conclusions: SMS2 deficiency in the macrophages reduces atherosclerosis in mice. Macrophage SMS2 is thus a potential therapeutic target for treatment of this disease.

Myeloid cell–specific serine palmitoyltransferase subunit 2 haploinsufficiency reduces murine atherosclerosis

Serine palmitoyltransferase (SPT) is the first and rate-limiting enzyme of the de novo biosynthetic pathway of sphingomyelin (SM). Both SPT and SM have been implicated in the pathogenesis of atherosclerosis, the development of which is driven by macrophages; however, the role of SPT in macrophage-mediated atherogenesis is unknown. To address this issue, we have analyzed macrophage inflammatory responses and reverse cholesterol transport, 2 key mediators of atherogenesis, in SPT subunit 2-haploinsufficient (Sptlc2(+/-)) macrophages. We found that Sptlc2(+/-) macrophages have significantly lower SM levels in plasma membrane and lipid rafts. This reduction not only impaired inflammatory responses triggered by TLR4 and its downstream NF-κB and MAPK pathways, but also enhanced reverse cholesterol transport mediated by ABC transporters. LDL receptor-deficient (Ldlr(-/-)) mice transplanted with Sptlc2(+/-) bone marrow cells exhibited significantly fewer atherosclerotic lesions after high-fat and high-cholesterol diet feeding. Additionally, Ldlr(-/-) mice with myeloid cell-specific Sptlc2 haploinsufficiency exhibited significantly less atherosclerosis than controls. These findings suggest that SPT could be a novel therapeutic target in atherosclerosis.

Mechanisms of interleukin-22's beneficial effects in acute pancreatitis.

Acute pancreatitis (AP) is a disorder characterized by parenchymal injury of the pancreas controlled by immune cell-mediated inflammation. AP remains a significant challenge in the clinic due to a lack of specific and effective treatment. Knowledge of the complex mechanisms that regulate the inflammatory response in AP is needed for the development of new approaches to treatment, since immune cell-derived inflammatory cytokines have been recognized to play critical roles in the pathogenesis of the disease. Recent studies have shown that interleukin (IL)-22, a cytokine secreted by leukocytes, when applied in the severe animal models of AP, protects against the inflammation-mediated acinar injury. In contrast, in a mild AP model, endogenous IL-22 has been found to be a predominantly anti-inflammatory mediator that inhibits inflammatory cell infiltration via the induction of Reg3 proteins in acinar cells, but does not protect against acinar injury in the early stage of AP. However, constitutively over-expressed IL-22 can prevent the initial acinar injury caused by excessive autophagy through the induction of the anti-autophagic proteins Bcl-2 and Bcl-XL. Thus IL-22 plays different roles in AP depending on the severity of the AP model. This review focuses on these recently reported findings for the purpose of better understanding IL-22s regulatory roles in AP which could help to develop a novel therapeutic strategy.

Liver serine palmitoyltransferase activity deficiency in early life impairs adherens junctions and promotes tumorigenesis

Serine palmitoyltransferase is the key enzyme in sphingolipid biosynthesis. Mice lacking serine palmitoyltransferase are embryonic lethal. We prepared liver‐specific mice deficient in the serine palmitoyltransferase long chain base subunit 2 gene using an albumin‐cyclization recombination approach and found that the deficient mice have severe jaundice. Moreover, the deficiency impairs hepatocyte polarity, attenuates liver regeneration after hepatectomy, and promotes tumorigenesis. Importantly, we show that the deficiency significantly reduces sphingomyelin but not other sphingolipids in hepatocyte plasma membrane; greatly reduces cadherin, the major protein in adherens junctions, on the membrane; and greatly induces cadherin phosphorylation, an indication of its degradation. The deficiency affects cellular distribution of β‐catenin, the central component of the canonical Wnt pathway. Furthermore, such a defect can be partially corrected by sphingomyelin supplementation in vivo and in vitro. Conclusion: The plasma membrane sphingomyelin level is one of the key factors in regulating hepatocyte polarity and tumorigenesis. (Hepatology 2016;64:2089‐2102).

Acinar cell injury induced by inadequate unfolded protein response in acute pancreatitis

Acute pancreatitis (AP) is an inflammatory disorder of pancreatic tissue initiated in injured acinar cells. Severe AP remains a significant challenge due to the lack of effective treatment. The widely-accepted autodigestion theory of AP is now facing challenges, since inhibiting protease activation has negligible effectiveness for AP treatment despite numerous efforts. Furthermore, accumulating evidence supports a new concept that malfunction of a self-protective mechanism, the unfolded protein response (UPR), is the driving force behind the pathogenesis of AP. The UPR is induced by endoplasmic reticulum (ER) stress, a disturbance frequently found in acinar cells, to prevent the aggravation of ER stress that can otherwise lead to cell injury. In addition, the UPR’s signaling pathways control NFκB activation and autophagy flux, and these dysregulations cause acinar cell inflammatory injury in AP, but with poorly understood mechanisms. We therefore summarize the protective role of the UPR in AP, propose mechanistic models of how inadequate UPR could promote NFκB’s pro-inflammatory activity and impair autophagy’s protective function in acinar cells, and discuss its relevance to current AP treatment. We hope that insight provided in this review will help facilitate the research and management of AP.

635 Acute Pancreatitis (AP) in Aging Animals-Loss of PAP Protection?

Background: Although acute inflammation is a critical protective response against injury and infection, persistent inflammation and the resulting oxidative stress drive the pathogenesis of numerous chronic degenerative diseases, including carcinogenesis. In human pancreatic ductal adenocarcinoma (PDA) and in animal models that recapitulate the disease progression, an intense fibroinflammatory reaction composed of stromal and immune cells accompanies the progression from normal histology to PDA. Angiotensin II (AngII), the principal hormone of the renin angiotensin system, is actively generated in the pancreas and has been proposed as a key mediator of inflammation. Monocyte chemoattractant protein(MCP)-1 is a chemokine that plays an important role in the recruitment of mononuclear cells into sites of inflammation. Objective: To investigate the potential proinflammatory role of AngII in PDA through studying its effect on MCP-1. Methods: PDA cells (AsPC-1, HS766T, MiaPaca) were cultured and treated with or without Ang II (10-8-10-6mol/L), in the presence or absence of AngII type 1 receptor blocker, losartan, or AngII type 2 receptor blocker, PD123319. MCP-1 mRNA was analyzed by real time PCR and its protein by ELISA. Luciferase-labeled promoter studies evaluated the effect of AngII on the transcription of MCP-1 and nuclear factor-κB (NF-κB). The effect of receptor blockers on the endogenous and AngII-induced activation and nuclear translocation of NF-kB was examined by luminescence assay and immunohistochemistry. Results: AngII significantly increased the expression ofMCP-1mRNA and protein in PDA cells, and induced its promoter activity. Constitutive and AngII-induced MCP-1 mRNA and promoter activity were significantly reduced in the presence of losartan but were unchanged by PD123319. AngII induced the activation and nuclear translocation of NF-kB, an effect that was inhibited by losartan, but not PD 1233319. Blocking NF-kB activation by pyrrolidine dithiocarbamate decreased the AngII-mediated increase in MCP1 mRNA. Conclusions: Our data provide a novel insight into an AngII-initiated signal transduction pathway that regulates MCP-1 as a possible inflammatory mechanism in PDA, and suggest that AngII blockade may regulate chemokine-induced signal transduction to prevent or reduce inflammation in PDA.