Ubiquinone deficiency drives reverse electron transport to disrupt hepatic metabolic homeostasis in obesity.

Mitochondrial reactive oxygen species (mROS) are central to physiology. While excess mROS production has been associated with several disease states, its precise sources, regulation, and mechanism of generation in vivo remain unknown, limiting translational efforts. Here we show that in obesity, hepatic ubiquinone (Q) synthesis is impaired, which raises the QH 2 /Q ratio, driving excessive mROS production via reverse electron transport (RET) from site I Q in complex I. Using multiple complementary genetic and pharmacological models in vivo we demonstrated that RET is critical for metabolic health. In patients with steatosis, the hepatic Q biosynthetic program is also suppressed, and the QH 2 /Q ratio positively correlates with disease severity. Our data identify a highly selective mechanism for pathological mROS production in obesity, which can be targeted to protect metabolic homeostasis.

Novel role of PKR in inflammasome activation and HMGB1 release.

The inflammasome regulates the release of caspase activation-dependent cytokines, including interleukin (IL)-1ß, IL-18 and high-mobility group box 1 (HMGB1). By studying HMGB1 release mechanisms, here we identify a role for double-stranded RNA-dependent protein kinase (PKR, also known as EIF2AK2) in inflammasome activation. Exposure of macrophages to inflammasome agonists induced PKR autophosphorylation. PKR inactivation by genetic deletion or pharmacological inhibition severely impaired inflammasome activation in response to double-stranded RNA, ATP, monosodium urate, adjuvant aluminium, rotenone, live Escherichia coli, anthrax lethal toxin, DNA transfection and Salmonella typhimurium infection. PKR deficiency significantly inhibited the secretion of IL-1ß, IL-18 and HMGB1 in E. coli-induced peritonitis. PKR physically interacts with several inflammasome components, including NOD-like receptor (NLR) family pyrin domain-containing 3 (NLRP3), NLRP1, NLR family CARD domain-containing protein 4 (NLRC4), absent in melanoma 2 (AIM2), and broadly regulates inflammasome activation. PKR autophosphorylation in a cell-free system with recombinant NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC, also known as PYCARD) and pro-caspase-1 reconstitutes inflammasome activity. These results show a crucial role for PKR in inflammasome activation, and indicate that it should be possible to pharmacologically target this molecule to treat inflammation.

Genetic deficiency and pharmacological stabilization of mast cells reduce diet-induced obesity and diabetes in mice.

Although mast cell functions have classically been related to allergic responses, recent studies indicate that these cells contribute to other common diseases such as multiple sclerosis, rheumatoid arthritis, atherosclerosis, aortic aneurysm and cancer. This study presents evidence that mast cells also contribute to diet-induced obesity and diabetes. For example, white adipose tissue (WAT) from obese humans and mice contain more mast cells than WAT from their lean counterparts. Furthermore, in the context of mice on a Western diet, genetically induced deficiency of mast cells, or their pharmacological stabilization, reduces body weight gain and levels of inflammatory cytokines, chemokines and proteases in serum and WAT, in concert with improved glucose homeostasis and energy expenditure. Mechanistic studies reveal that mast cells contribute to WAT and muscle angiogenesis and associated cell apoptosis and cathepsin activity. Adoptive transfer experiments of cytokine-deficient mast cells show that these cells, by producing interleukin-6 (IL-6) and interferon-gamma (IFN-gamma), contribute to mouse adipose tissue cysteine protease cathepsin expression, apoptosis and angiogenesis, thereby promoting diet-induced obesity and glucose intolerance. Our results showing reduced obesity and diabetes in mice treated with clinically available mast cell-stabilizing agents suggest the potential of developing new therapies for these common human metabolic disorders.

Stressing the brain, fattening the body.

Obesity is characterized by chronic activation of inflammatory pathways in peripheral tissues. In this issue, Zhang et al. (2008) demonstrate that inflammation also occurs in the central nervous system where it disrupts activity of the hypothalamus leading to resistance to leptin that is mediated by activation of IKK and the endoplasmic reticulum stress response.

Habitual dietary intake of n-3 and n-6 fatty acids in relation to inflammatory markers among US men and women.

BACKGROUND: Polyunsaturated fatty acid intake favorably affects chronic inflammatory-related diseases such as cardiovascular disease; however, high intake of n-6 fatty acids may attenuate the known beneficial effects of n-3 fatty acids. METHODS AND RESULTS: We investigated habitual dietary n-3 fatty acid intake and its interaction with n-6 fatty acids in relation to the plasma inflammatory markers C-reactive protein, interleukin 6, and soluble tumor necrosis factor receptors 1 and 2 (sTNF-R1 and R2) among 405 healthy men and 454 healthy women. After adjustment for other predictors of inflammation, intake of the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was inversely associated with plasma levels of sTNF-R1 and sTNF-R2 (P=0.03 and P<0.001, respectively) and somewhat less so for C-reactive protein (P=0.08). n-3 alpha-linolenic acid and n-6 cis-linoleic acid were not significantly related to the inflammatory markers. We found little if any association between n-3 fatty acid (EPA+DHA) intake and tumor necrosis factor receptors among participants with low intake of n-6 but a strong inverse association among those with high n-6 intake (P=0.04 and 0.002 for interaction of n-3 with n-6 on sTNF-R1 and sTNF-R2, respectively). CONCLUSIONS: These results suggest that n-6 fatty acids do not inhibit the antiinflammatory effects of n-3 fatty acids and that the combination of both types of fatty acids is associated with the lowest levels of inflammation. The inhibition of inflammatory cytokines may be one possible mechanism for the observed beneficial effects of these fatty acids on chronic inflammatory-related diseases.