Igor Bykov

Defective insulin receptor activation and altered lipid rafts in Niemann–Pick type C disease hepatocytes

Niemann-Pick type C (NPC) disease is a neuro-visceral cholesterol storage disorder caused by mutations in the NPC-1 or NPC-2 gene. In the present paper, we studied IR (insulin receptor) activation and the plasma-membrane lipid assembly in primary hepatocytes from control and NPC1-/- mice. We have previously reported that, in hepatocytes, IR activation is dependent on cholesterol-sphingolipid rafts [Vainio, Heino, Mansson, Fredman, Kuismanen, Vaarala and Ikonen (2002) EMBO Rep. 3, 95-100]. We found that, in NPC hepatocytes, IR levels were up-regulated and the receptor activation was compromised. Defective IR activation was reproduced in isolated NPC plasma-membrane preparations, which displayed an increased cholesterol content and saturation of major phospholipids. The NPC plasma membranes were less fluid than control membranes as indicated by increased DPH (1,6-diphenyl-1,3,5-hexatriene) fluorescence anisotropy values. Both in NPC hepatocytes and plasma-membrane fractions, the association of IR with low-density DRMs (detergent-resistant membranes) was increased. Moreover, the detergent resistance of both cholesterol and phosphatidylcholine were increased in NPC membranes. Finally, cholesterol removal inhibited IR activation in control membranes but restored IR activation in NPC membranes. Taken together, the results reveal a lipid imbalance in the NPC hepatocyte, which increases lipid ordering in the plasma membrane, alters the properties of lipid rafts and interferes with the function of a raft-associated plasma-membrane receptor. Such a mechanism may participate in the pathogenesis of NPC disease and contribute to insulin resistance in other disorders of lipid metabolism.

Complement C3 contributes to ethanol-induced liver steatosis in mice.

Background. It is becoming increasingly clear that liver steatosis, a typical early consequence of alcohol exposure, sensitizes the liver to more severe inflammatory and fibrotic changes. On the other hand, activation of the key complement component C3, a central player in causing inflammation and tissue damage, is also known to be involved in the regulation of lipid metabolism. This prompted us to study the development of alcoholic liver steatosis in mice lacking C3 (C3−/−). Results. Both C3−/− and normal C3+/+ mice were fed a steatosis‐promoting high‐fat diet with or without ethanol for 6 weeks. The diet without ethanol caused moderate liver steatosis in C3−/− but not in C3+/+ mice. As expected, ethanol‐containing diet caused marked macrovesicular steatosis and increased the liver triglyceride content in C3+/+ mice. In contrast, ethanol diet tended to reduce steatosis and had no further effect on liver triglycerides in C3−/− mice. Furthermore, while in normal mice ethanol significantly increased the liver/body weight ratio, liver malondialdehyde level and serum alanine aminotransferase (ALT) activity, these effects were absent or small in C3−/− mice. A separate experiment with mice on chow diet confirmed the aberrant steatotic effect of ethanol in C3−/−mice: 4 hours after acute dosing of ethanol the liver triglyceride level had increased by 138% in C3+/+ mice (P<0.001), but only by 64% in C3−/− mice (n.s.). Conclusion. In C3−/− mice alcohol‐induced liver steatosis is absent or strongly reduced after chronic or acute alcohol exposure. This suggests that the complement system and its component C3 contribute to the development of alcohol‐induced fatty liver and its consequences.

Chlamydial and Periodontal Pathogens Induce Hepatic Inflammation and Fatty Acid Imbalance in Apolipoprotein E-Deficient Mice

ABSTRACT Periodontitis and Chlamydia pneumoniae infection are independent risk factors for cardiovascular diseases. The aim of this study was to investigate the effect of C. pneumoniae and Aggregatibacter actinomycetemcomitans infection on hepatic inflammation and lipid homeostasis of apolipoprotein E-deficient mice. Mice were infected with viable C. pneumoniae intranasally three times for chronic infection or once for acute infection. Viable A. actinomycetemcomitans was administered 10 times intravenously alone or in concert with C. pneumoniae. Hepatic alterations were assessed by histochemistry, lipid quantification, and fatty acid profile analysis. The RNA expression levels and the presence of pathogens in the livers and lungs were detected by quantitative real-time PCR. Both pathogens were detected in the livers of the infected animals. Chronic C. pneumoniae infection induced marked changes in hepatic lipid homeostasis. A. actinomycetemcomitans infection resulted in inflammatory cell infiltration into the liver, accompanied by elevated hepatic RNA expression levels of inflammation-related genes and higher serum amyloid A and lipopolysaccharide concentrations. Our results indicate that proatherogenic pathogens infect the liver, causing proinflammatory alterations and lipid disturbances. This infection may maintain chronic systemic inflammation attributable to atherogenesis.

Functional Differences between Periportal and Perivenous Kupffer Cells Isolated by Digitonin-Collagenase Perfusion

Liver injury commonly appears in a zonated fashion within the liver acinus. Thus many hepatotoxins primarily damage the perivenous (centrilobular, PV) region [1]. It is now well established that Kupffer cells (KCs) play a crucial role as initiators and mediators of the inflammatory process in the liver through the release of inflammatory and immunomodulatory mediators. However, the role of KCs in initiating regional damage is not established. Several studies based on immunohistochemistry have shown that the KCs in the periportal (PP) area are larger and cell size separation based on elutriation suggest that they are more active in phagocytosis [2-5]. The evidence suggesting that the smaller KCs in the centrilobular region would be more active in cytokine production is not clear-cut [3,4]. The aim of this study was to isolate KCs from different parts of the liver acinus and compare their capacity for phagocytosis and for secretion of key molecules mediating cytotoxicity.