Galectin-3 ablation protects mice from diet-induced NASH: a major scavenging role for galectin-3 in liver.

BACKGROUND & AIMS: Excess fatty acid oxidation and generation of reactive carbonyls with formation of advanced lipoxidation endproducts (ALEs) is involved in nonalcoholic steatohepatitis (NASH) by triggering inflammation, hepatocyte injury, and fibrosis. This study aimed at verifying the hypothesis that ablation of the ALE-receptor galectin-3 prevents experimental NASH by reducing receptor-mediated ALE clearance and downstream events. METHODS: Galectin-3-deficient (Lgals3(-/-)) and wild type (Lgals3(+/+)) mice received an atherogenic diet or standard chow for 8 months. Liver tissue was analyzed for morphology, inflammation, cell and matrix turnover, lipid metabolism, ALEs, and ALE-receptors. RESULTS: Steatosis was significantly less pronounced in Lgals3(-/-) than Lgals3(+/+) animals on atherogenic diet. NASH, invariably detected in Lgals3(+/+) mice, was observed, to a lower extent, only in 3/8 Lgals3(-/-) mice, showing less inflammatory, degenerative, and fibrotic phenomena than Lgals3(+/+) mice. This was associated with higher circulating ALE levels and lower tissue ALE accumulation and expression of other ALE-receptors. Up-regulation of hepatic fatty acid synthesis and oxidation, inflammatory cell infiltration, pro-inflammatory cytokines, endoplasmic reticulum stress, hepatocyte apoptosis, myofibroblast transdifferentiation, and impaired Akt phosphorylation were also significantly attenuated in Lgals3(-/-) animals. Galectin-3 silencing in liver endothelial cells resulted in reduced N(ε)-carboxymethyllysine-modified albumin uptake and ALE-receptor expression. CONCLUSIONS: Galectin-3 ablation protects from diet-induced NASH by decreasing hepatic ALE accumulation, with attenuation of inflammation, hepatocyte injury, and fibrosis. It also reduced up-regulation of lipid synthesis and oxidation causing less fat deposition, oxidative stress, and possibly insulin resistance. These data suggest that galectin-3 is a major receptor involved in ALE uptake by the liver.

Advanced lipoxidation end-products mediate lipid-induced glomerular injury: role of receptor-mediated mechanisms.

Atherosclerosis and renal disease are related conditions, sharing several risk factors. This includes hyperlipidaemia, which may result in enhanced lipoprotein accumulation and chemical modification, particularly oxidation, with formation of advanced lipoxidation endproducts (ALEs). We investigated whether increased lipid peroxidation plays a major role in the pathogenesis of lipid-induced renal disease, via receptor-mediated mechanisms involving the scavenger and advanced glycation endproduct (AGE) receptors. Mice knocked out for galectin-3 (Gal3(-/-)), an AGE receptor previously shown to protect from AGE-induced renal injury, and the corresponding wild-type (Gal3(+/+)) animals, were fed an atherogenic high-fat diet (HFD; 15% fat, 1.25% cholesterol and 0.5% sodium cholate); mice fed a normal-fat diet (NFD; 4% fat) served as controls. Gal3(+/+) mice fed a HFD developed glomerular disease, as indicated by proteinuria, mesangial expansion and glomerular hypertrophy and sclerosis. Glomerular injury was associated with increased glomerular matrix protein expression, ALE and oxidized LDL content, oxidative stress, AGE and scavenger receptor expression and macrophage infiltration, with only modest renal/glomerular fat accumulation and changes in lipid metabolism. Fibrotic and inflammatory changes, together with accumulation of ALEs, such as 4-hydroxy-2-nonenal adducts and N(epsilon)-carboxymethyllysine, oxidative stress and expression of the receptor of AGEs (RAGE), were significantly more marked in Gal3(-/-) animals, whereas fat deposition and abnormalities in lipid metabolism remained modest. Thus, lipid-induced renal damage is mainly dependent on lipid peroxidation with formation of carbonyl reactive species and ALEs, which accumulate within the kidney tissue, thus triggering receptor-mediated pro-inflammatory signalling pathways, as in atherogenesis. Moreover, galectin-3 exerts a significant role in the uptake and effective removal of modified lipoproteins, with diversion of these products from RAGE-dependent pro-inflammatory pathways associated with downregulation of RAGE expression.

Accelerated lipid-induced atherogenesis in galectin-3-deficient mice: role of lipoxidation via receptor-mediated mechanisms.

OBJECTIVE: Modified lipoproteins, particularly oxidized LDLs, are believed to evoke an inflammatory response which participates in all stages of atherosclerosis. Disposal of these particles is mediated through receptors which may trigger proinflammatory signaling pathways leading to vascular injury. This study was aimed at assessing the role in atherogenesis of one of these receptors, galectin-3. METHODS AND RESULTS: Galectin-3-deficient and wild-type mice were fed an atherogenic diet or standard chow for 8 months. Lesion area and length were higher in galectin-3-deficient versus wild-type mice. At the level of the aortic sinus, wild-type animals showed only fatty streaks, whereas galectin-3-deficient mice developed complex lesions, associated with extensive inflammatory changes. This was indicated by the presence of T lymphocytes with activated Th1-phenotype and by more marked monocyte-macrophage infiltration, inflammatory mediator expression, vascular cell apoptosis, and proinflammatory transcription factor activation. Increased accumulation of oxidixed LDLs and lipoxidation products and upregulation of other receptors for these compounds, including the proinflammatory RAGE, were detected in galectin-3-deficient versus wild-type mice. CONCLUSIONS: These data suggest a unique protective role for galectin-3 in the uptake and effective removal of modified lipoproteins, with concurrent downregulation of proinflammatory pathways responsible for atherosclerosis initiation and progression.

Oxidative stress in diabetes-induced endothelial dysfunction involvement of nitric oxide and protein kinase C.

Reactive oxygen species (ROS) formation plays a major role in diabetes-induced endothelial dysfunction, though the molecular mechanism(s) involved and the contribution of nitric oxide (NO) are still unclear. This study using bovine retinal endothelial cells was aimed at assessing (i) the role of oxygen-dependent vs. NO-dependent oxidative stress in the endothelial cell permeability alterations induced by the diabetic milieu and (ii) whether protein kinase C (PKC) activation ultimately mediates these changes. Superoxide, lipid peroxide, and PKC activity were higher under high glucose (HG) vs. normal glucose throughout the 30 d period. Nitrite/nitrate and endothelial NO synthase levels increased at 1 d and decreased thereafter. Changes in monolayer permeability to 125I-BSA induced by 1 or 30 d incubation in HG or exposure to advanced glycosylation endproduct were reduced by treatment with antioxidants or PKC inhibitors, whereas NO blockade prevented only the effect of 1 d HG. HG-induced changes were mimicked by a PKC activator, a superoxide generating system, an NO and superoxide donor, or peroxynitrite (attenuated by PKC inhibition), but not a NO donor. The short-term effect of HG depends on a combined oxidative and nitrosative stress with peroxynitrite formation, whereas the long-term effect is related to ROS generation; in both cases, PKC ultimately mediates permeability changes.