A latitudinal gradient in biodiversity has existed since before the time of the dinosaurs, yet how and why this gradient arose remains unresolved. Here we review two major hypotheses for the origin of the latitudinal diversity gradient. The time and area hypothesis holds that tropical climates are older and historically larger, allowing more opportunity for diversification. This hypothesis is supported by observations that temperate taxa are often younger than, and nested within, tropical taxa, and that diversity is positively correlated with the age and area of geographical regions. The diversification rate hypothesis holds that tropical regions diversify faster due to higher rates of speciation (caused by increased opportunities for the evolution of reproductive isolation, or faster molecular evolution, or the increased importance of biotic interactions), or due to lower extinction rates. There is phylogenetic evidence for higher rates of diversification in tropical clades, and palaeontological data demonstrate higher rates of origination for tropical taxa, but mixed evidence for latitudinal differences in extinction rates. Studies of latitudinal variation in incipient speciation also suggest faster speciation in the tropics. Distinguishing the roles of history, speciation and extinction in the origin of the latitudinal gradient represents a major challenge to future research.

SUMMARY Normal platelet function is critical to blood hemostasis and maintenance of a closed circulatory system. Heightened platelet reactivity, however, is associated with cardiometabolic diseases and enhanced potential for thrombotic events. We now show gut microbes, through generation of trimethylamine N-oxide (TMAO), directly contribute to platelet hyperreactivity and enhanced thrombosis potential. Plasma TMAO levels in subjects (N>4000) independently predicted incident (3 yr) thrombosis (heart attack, stroke) risk. Direct exposure of platelets to TMAO enhanced submaximal stimulus-dependent platelet activation from multiple agonists through augmented Ca2+ release from intracellular stores. Animal model studies employing dietary choline or TMAO, germ-free mice, and microbial transplantation, collectively confirm a role for gut microbiota and TMAO in modulating platelet hyperresponsiveness and thrombosis potential, and identify microbial taxa associated with plasma TMAO and thrombosis potential. Collectively, the present results reveal a previously unrecognized mechanistic link between specific dietary nutrients, gut microbes, platelet function, and thrombosis risk.

Macrophage-specific Abca1 knock-out (Abca1؊M/؊M ) mice were generated to determine the role of macrophage ABCA1 expression in plasma lipoprotein concentrations and the innate immune response of macrophages. Plasma lipid and lipoprotein concentrations in chow-fed Abca1 ؊M/؊M and wild-type (WT) mice were indistinguishable. Compared with WT macrophages, Abca1 ؊M/؊M macrophages had a >95% reduction in ABCA1 protein, failed to efflux lipid to apoA-I, and had a significant increase in free cholesterol (FC) and membrane lipid rafts without induction of endoplasmic reticulum stress. Lipopolysaccharide (LPS)-treated Abca1 ABCA1 (ATP-binding cassette transporter A1) is a plasma membrane protein that is widely expressed throughout the body (1, 2) and functions as a primary gatekeeper for eliminating excess free cholesterol (FC) 2 from tissues by effluxing cellular FC and phospholipid (PL) to lipid-free apoA-I, resulting in the formation of nascent high density lipoprotein (HDL) particles (3, 4). The nascent discoid-shaped HDL then undergoes a maturation process that involves additional lipid acquisition and conversion of FC to cholesteryl ester (CE) by lecithin:cholesterol acyltransferase to become mature spherical plasma HDL. Mutations that inactivate the human ABCA1 gene result in Tangier disease, which is characterized by extremely low HDL cholesterol concentrations, mildly elevated plasma trigelyceride levels, and accumulation of cholesterol in macrophages (5-10). Targeted deletion of Abca1 in mice and a natural mutation of Abca1 in the Wisconsin hypoalpha mutant chicken recapitulate the Tangier plasma lipid phenotype, supporting the essential role of ABCA1 in HDL formation (11-15). Although ABCA1 is expressed in many cells in the body, recent studies in hepatocyte-and intestinal epithelium-specific Abca1 knock-out mice suggest that the liver contributes 70 -80% of the plasma HDL pool, whereas the intestine contributes 20 -30% (16, 17). Although mobilization of excess FC from macrophages is dependent on ABCA1 and results in the formation of nascent HDL particles, transplantation of bone marrow from Abca1 knock-out (KO) mice into wild-type (WT) mice or transplantation of WT marrow into Abca1 KO recipients has little effect on plasma HDL concentrations, suggesting that macrophage ABCA1 expression has minimal impact on plasma HDL concentrations (18,19).Macrophages are a primary cell type involved in innate immunity. Although macrophage ABCA1 has a minimal impact on plasma lipid levels, there is evidence that its activity modulates the inflammatory response of macrophages to pathogen-associated molecules such as lipopolysaccharide

Trimethylamine-N-oxide (TMAO), a microbiota-dependent metabolite derived from trimethylamine (TMA)-containing nutrients that are abundant in a Western diet, enhances both platelet responsiveness and in vivo thrombosis potential in animal models and predicts incident atherothrombotic event risks in clinical studies. Here, utilizing a mechanism-based inhibitor approach targeting a major microbial TMA-generating enzyme (CutC/D), we developed potent, time-dependent and irreversible inhibitors that do not affect commensal viability. In animal models, a single oral dose of a CutC/D inhibitor significantly reduced plasma TMAO levels for up to 3 days and rescued diet-induced enhanced platelet responsiveness and thrombus formation, without observable toxicity or increased bleeding risk. The inhibitor selectively accumulated within intestinal microbes to millimolar levels, a concentration over a million-fold higher than needed for a therapeutic effect. These studies reveal that mechanism-based inhibition of gut microbial TMA/TMAO production reduces thrombosis potential, a critical adverse complication in heart disease. They also offer a generalizable approach for the selective non-lethal targeting of gut microbial enzymes linked to host disease, while limiting systemic exposure of the inhibitor in the host.

The human gastrointestinal tract is home to trillions of bacteria, which vastly outnumber host cells in the body. Although generally overlooked in the field of endocrinology, gut microbial symbionts organize to form a key endocrine organ that convert nutritional cues from the environment into hormone-like signals that impact both normal physiology and chronic disease in the human host. Recent evidence suggests that several gut microbial-derived products are sensed by dedicated host receptor systems to alter cardiovascular disease (CVD) progression. In fact, gut microbial metabolism of dietary components results in the production of proatherogenic circulating factors that act through a meta-organismal endocrine axis to impact CVD risk. Whether pharmacological interventions at the level of the gut microbial endocrine organ will reduce CVD risk is a key new question in the field of cardiovascular medicine. Here we discuss the opportunities and challenges that lie ahead in targeting meta-organismal endocrinology for CVD prevention.

Although diet has long been known to contribute to the pathogenesis of cardiovascular disease (CVD), research over the past decade has revealed an unexpected interplay between nutrient intake, gut microbial metabolism and the host to modify the risk of developing CVD. Microbial-associated molecular patterns are sensed by host pattern recognition receptors and have been suggested to drive CVD pathogenesis. In addition, the host microbiota produces various metabolites, such as trimethylamine-N-oxide, short chain fatty acids and secondary bile acids, that affect CVD pathogenesis. These recent advances support the notion that targeting the interactions between the host and microorganisms may hold promise for the prevention or treatment of CVD. In this Review, we summarize our current knowledge of the gut microbial mechanisms that drive CVD, with special emphasis on therapeutic interventions, and we highlight the need to establish causal links between microbial pathways and CVD pathogenesis

Animal taxa show remarkable variability in species richness across phylogenetic groups. Most explanations for this disparity postulate that taxa with more species have phenotypes or ecologies that cause higher diversification rates (i.e., higher speciation rates or lower extinction rates). Here we show that clade longevity, and not diversification rate, has primarily shaped patterns of species richness across major animal clades: more diverse taxa are older and thus have had more time to accumulate species. Diversification rates calculated from 163 species-level molecular phylogenies were highly consistent within and among three major animal phyla (Arthropoda, Chordata, Mollusca) and did not correlate with species richness. Clades with higher estimated diversification rates were younger, but species numbers increased with increasing clade age. A fossil-based data set also revealed a strong, positive relationship between total extant species richness and crown group age across the orders of insects and vertebrates. These findings do not negate the importance of ecology or phenotype in influencing diversification rates, but they do show that clade longevity is the dominant signal in major animal biodiversity patterns. Thus, some key innovations may have acted through fostering clade longevity and not by heightening diversification rate.

Trans-10,cis-12 conjugated linoleic acid (CLA) has previously been shown to be the CLA isomer responsible for CLA-induced reductions in body fat in animal models, and we have shown that this isomer, but not the cis-9,trans-11 CLA isomer, specifically decreased triglyceride (TG) accumulation in primary human adiopcytes in vitro. Here we investigated the mechanism behind the isomerspecific, CLA-mediated reduction in TG accumulation in differentiating human preadipocytes. Trans-10,cis-12 CLA decreased insulin-stimulated glucose uptake and oxidation, and reduced insulin-dependent glucose transporter 4 gene expression. Furthermore, trans-10,cis-12 CLA reduced oleic acid uptake and oxidation when compared with all other treatments. In parallel to CLA's effects on metabolism, trans-10,cis-12 CLA decreased, whereas cis-9,trans-11 CLA increased, the expression of peroxisome proliferator-activated receptor γ (PPARγ) and several of its downstream target genes when compared with vehicle controls. Transient transfections demonstrated that both CLA isomers antagonized ligand-dependent activation of PPARγ. Collectively, trans-10,cis-12, but not cis-9, trans-11, CLA decreased glucose and lipid uptake and oxidation and preadipocyte differentiation by altering preadipocyte gene transcription in a manner that appeared to be due, in part, to decreased PPARγ expression. Supplementary key wordsconjugated linoleic acid; fatty acids; lipid metabolism; glucose metabolism; triglycerides; peroxisome proliferator-activated receptor gamma Abbreviations ACBP, acyl-CoA binding protein; ACC, acetyl-CoA carboxylase; aP2/FABP, adipocyte fatty acid binding protein; BCA, bicinchoninic acid; BMI, body mass index; BSA, bovine serum albumin; CD-36, fatty acid translocase; C/EBPα, CAAT/enhancer binding protein α; CLA, conjugated linoleic acid; GC, gas chromatography; GLUT4, insulin-dependent glucose transporter 4; GPDH, glycerol-3-phosphate dehydrogenase; HSL, hormone-sensitive lipase; IBMX, isobutylmethylxanthine; LA, linoleic acid; LPL, lipoprotein lipase; MUFA, monounsaturated fatty acid; ORO, oil red O; PPAR, 1 To whom correspondence should be addressed. e-mail:mkmcinto@uncg.edu. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript peroxisome proliferator-activated receptor; PPRE, peroxisome proliferator response element; SCD-1, stearoyl-CoA desaturase-1; SFA, saturated fatty acid; SV, stromal vascular; TG, triglyceride Conjugated linoleic acid (CLA) refers to a group of geometric and positional dienoic isomers of linoleic acid (LA) [18:2(n-6)]. The two predominant isomers of CLA found in food and commercial preparations are cis-9,trans-11 CLA and trans-10,cis-12 CLA. CLA is found in ruminant meats, pasteurized cheeses, and dairy products, and therefore is a natural part of the diet. CLA has been extensively studied due to its potentially beneficial effects on carcinogenesis (1-3), diabetes (4,5), atherosclerosis (6,7), immune function (8-10), and body composition (11)(12)(13)(14)(15)(16).Collectivel...