Olivier Molendi-Coste

Kupffer cell activation is a causal factor for hepatic insulin resistance.

Recruited adipose tissue macrophages contribute to chronic and low-grade inflammation causing insulin resistance in obesity. Similarly, we hypothesized here that Kupffer cells, the hepatic resident macrophages, play a pathogenic role in hepatic insulin resistance induced by a high-fat diet. Mice were fed a normal diet or high-fat diet for 3 days. Kupffer cell activation was evaluated by immunohistochemistry and quantitative RT-PCR. Insulin sensitivity was assessed in vivo by hyperinsulinemic-euglycemic clamp and insulin-activated signaling was investigated by Western blot. Liposome-encapsulated clodronate was injected intravenously to deplete macrophages prior to a short-term exposure to high-fat diet. Here, we characterized a short-term high-fat diet model in mice and demonstrated early hepatic insulin resistance and steatosis concurrent with Kupffer cell activation. We demonstrated that selective Kupffer cell depletion obtained by intravenous clodronate, without affecting adipose tissue macrophages, was sufficient to enhance insulin-dependent insulin signaling and significantly improve hepatic insulin sensitivity in vivo in this short-term high-fat diet model. Our study clearly shows that hepatic macrophage response participates to the onset of high-fat diet-induced hepatic insulin resistance and may therefore represent an attractive target for prevention and treatment of diet- and obesity-induced insulin resistance.

Why and How Meet n-3 PUFA Dietary Recommendations?

Obesity and the metabolic syndrome are systemic inflammatory diseases reaching epidemic proportions. Contemporary changes in human nutrition occurred characterized by increased consumption of fat and of vegetable oils rich in n-6 polyunsaturated fatty acids (PUFAs) together with decrease in n-3 PUFA-rich foods, resulting in an n-6/n-3 ratio of 10–20/1 in Western diet for a ratio around 1/1 in the diet of our ancestors. The literature provides compelling evidence for the health benefit of n-3 PUFA consumption on inflammation and metabolic syndrome prevention and treatment. Such evidence led to the establishment of comprehensive recommendations. However, we show here that, both in collective catering proposed to children and in hospital diet, it is not straightforward to meet such recommendations. Willingness of governments to institute changes, with accountable decisions on catering, nutritional education, and food processing, is required to face our neglected responsibility in promoting balanced diet and consumption of foods rich in essential nutrients in the general population.

Kupffer cell depletion prevents but has no therapeutic effect on metabolic and inflammatory changes induced by a high-fat diet

We aimed to evaluate activation of macrophages in insulin‐sensitive tissues (liver, adipose tissue, and muscles) under high‐fat diet (HFD) and elucidate the role of Kupffer cells (KC) in HFD‐induced insulin resistance. Tissue macrophage populations, insulin signaling, and sensitivity were evaluated in mice fed a HFD for 4 or 16 wk. Selective KC depletion was obtained by intravenous injections of liposome‐encapsulated clodronate. Mice fed a HFD for 4 to 16 wk have hepatic and peripheral insulin resistance together with macrophage recruitment in the adipose tissue but not in the liver. Depletion of KC for the last 10 d of the 16 wk experiment fails to improve insulin sensitivity compared to PBS‐treated animals. In contrast, preventive KC depletion prior to and during the 4 wk HFD attenuates the development of obesity, adiposity, adipose tissue inflammation (P<0.01 vs. PBS group), and insulin resistance (P<0.01). Interestingly, in mice fed a normal diet, prolonged KC depletion ameliorates insulin sensitivity and decreases adiposity without altering physiological body weight gain or food intake. Preventive and prolonged KC depletion ameliorates insulin sensitivity and prevents adipose tissue inflammation, suggesting a communication between the liver and the adipose tissue in the development of HFD‐induced metabolic alterations.—Lanthier, N., Molendi‐Coste, O., Cani, P. D., van Rooijen, N., Horsmans, Y., Leclercq, I. A. Kupffer cell depletion prevents but has no therapeutic effect on metabolic and inflammatory changes induced by a high‐fat diet. FASEB J. 25, 4301–4311 (2011). www.fasebj.org

Hepatic n-3 polyunsaturated fatty acid depletion promotes steatosis and insulin resistance in mice : genomic analysis of cellular targets.

Patients with non-alcoholic fatty liver disease are characterised by a decreased n-3/n-6 polyunsaturated fatty acid (PUFA) ratio in hepatic phospholipids. The metabolic consequences of n-3 PUFA depletion in the liver are poorly understood. We have reproduced a drastic drop in n-3 PUFA among hepatic phospholipids by feeding C57Bl/6J mice for 3 months with an n-3 PUFA depleted diet (DEF) versus a control diet (CT), which only differed in the PUFA content. DEF mice exhibited hepatic insulin resistance (assessed by euglycemic-hyperinsulinemic clamp) and steatosis that was associated with a decrease in fatty acid oxidation and occurred despite a higher capacity for triglyceride secretion. Microarray and qPCR analysis of the liver tissue revealed higher expression of all the enzymes involved in lipogenesis in DEF mice compared to CT mice, as well as increased expression and activation of sterol regulatory element binding protein-1c (SREBP-1c). Our data suggest that the activation of the liver X receptor pathway is involved in the overexpression of SREBP-1c, and this phenomenon cannot be attributed to insulin or to endoplasmic reticulum stress responses. In conclusion, n-3 PUFA depletion in liver phospholipids leads to activation of SREBP-1c and lipogenesis, which contributes to hepatic steatosis.

Impact of PPAR-α induction on glucose homoeostasis in alcohol-fed mice.

Alcohol consumption is a major cause of liver disease. It also associates with increased cardiovascular risk and Type 2 diabetes. ALD (alcoholic liver disease) and NAFLD (non-alcoholic fatty liver disease) share pathological features, pathogenic mechanisms and pattern of disease progression. In NAFLD, steatosis, lipotoxicity and liver inflammation participate to hepatic insulin resistance. The aim of the present study was to verify the effect of alcohol on hepatic insulin sensitivity and to evaluate the role of alcohol-induced steatosis and inflammation on glucose homoeostasis. C57BL/6J mice were fed for 20 days a modified Lieber-DeCarli diet in which the alcohol concentration was gradually increased up to 35% of daily caloric intake. OH (alcohol liquid diet)-fed mice had liver steatosis and inflammatory infiltration. In addition, these mice developed insulin resistance in the liver, but not in muscles, as demonstrated by euglycaemic-hyperinsulinaemic clamp and analysis of the insulin signalling cascade. Treatment with the PPAR-α (peroxisome-proliferator-activated receptor-α) agonist Wy14,643 protected against OH-induced steatosis and KC (Kupffer cell) activation and almost abolished OH-induced insulin resistance. As KC activation may modulate insulin sensitivity, we repeated the clamp studies in mice depleted in KC to decipher the role of macrophages. Depletion of KC using liposomes-encapsuled clodronate in OH-fed mice failed both to improve hepatic steatosis and to restore insulin sensitivity as assessed by clamp. Our study shows that chronic alcohol consumption induces steatosis, KC activation and hepatic insulin resistance in mice. PPAR-α agonist treatment that prevents steatosis and dampens hepatic inflammation also prevents alcohol-induced hepatic insulin resistance. However, KC depletion has little impact on OH-induced metabolic disturbances.

P0950 : Impact of kupffer cells on high fat induced insulin resistance and liver fetuin-A expression

Backgroun and aims: Hepatokines (liver secreted proteins with possible distant action) are emerging potential players in insulin resistance in type 2 diabetic patients. Here, we explore the effect of a high fat diet on the expression of fetuin-A, one of those candidate liver proteins, and its relation with liver macrophage (Kupffer cell) activation. Methods: Male mice of 5 weeks of age were fed a normal diet (ND) or a high fat diet (HFD) for 3 days, known to initiate steatosis and insulin resistance. A preventive Kupffer cell (KC) depletion was obtained by intravenous injection of clodronate loaded liposomes and compared with PBS liposomes. The mRNA and protein expression of fetuin-A was evaluated by RT-PCR, Western-blot and immunofluorescence (IF) on different insulin-sensitive tissues (liver, adipose tissue and muscle). Results: Short term HFD induced steatosis, KC activation and insulin resistance together with a significant increased expression of liver fetuin-A mRNA (1.5 fold, p<0.01). However, liver fetuin-A protein expression remained unchanged under short term HFD. This increase in fetuin-A under high fat diet was not evidenced in the peripheral insulin sensitive tissues (skeletal muscle and adipose tissue) whether at the mRNA or at the protein level. Kupffer cell depletion in this setting did not reduce hepatic steatosis but significantly ameliorated insulin sensitivity proved by clamp studies. This amelioration in insulin sensitivity in KC-depleted mice was associated with a significant decrease in fetuin-A mRNA expression (0.7 fold, p<0.01) compared to animals with KC. On immunofluorescence, fetuin-A was mostly expressed in centrilobular hepatocytes. Interestingly, while selectively depleting liver macrophages without affecting adipose tissue macrophage infiltration, intravenous clodronate injection was associated with a significant reduction in epididymal adipose tissue expansion compared to PBS injection (1.1% of body weight versus 1.6% of body weight, p<0.001). Conclusion: This study demonstrates liver fetuin-A overexpression at the initiation of HFD feeding, concurrent with hepatic steatosis and insulin resistance. Targeting KC in this setting improved insulin sensitivity and was associated with a decreased adiposity and a reduced liver fetuin-A expression suggesting that fetuin-A acts as an hepatokine with pro-adiposity and pro-insulin resistance effects.