First conceptualized as a mechanism for the mitochondrial transport of long-chain fatty acids in the early 1960s, the carnitine palmitoyltransferase (CPT) system has since come to be recognized as a pivotal component of fuel homeostasis. This is by virtue of the unique sensitivity of the outer membrane CPT I to the simple molecule, malonyl-CoA. In addition, both CPT I and the inner membrane enzyme, CPT 11, have proved to be loci of inherited defects, some with disastrous consequences. Early efforts using classical approaches to characterize the CPT proteins in terms of structure/function/regulatory relationships gave rise to confusion and protracted debate. By contrast, recent application of molecular biological tools has brought major enlightenment at an exponential pace. Here we review some key developments of the last 20 years that have led to our current understanding of the physiology of the CPT system, the structure of the CPT isofornis, the chromosomal localization of their respective genes, and the identification of mutations in the human population.

Recent studies have implicated inhibitor of B kinase (IKK) in mediating fatty acid (FA)-induced insulin resistance. How IKK causes these effects is unknown. The present study addressed the role of nuclear factor B (NFB), the distal target of IKK activity, in FA-induced insulin resistance in L6 myotubes, an in vitro skeletal muscle model. A 6-h exposure of myotubes to the saturated FA palmitate reduced insulin-stimulated glucose uptake by ϳ30%, phosphatidylinositol-3 kinase and protein kinase B phosphorylation by ϳ40%, and stimulated inhibitor of B␣ degradation and the nuclear translocation of NFB. On the other hand, the ⍀-3 polyunsaturated FA linolenate neither induced insulin resistance nor promoted nuclear localization of NFB. Supporting the hypothesis that IKK acts through NFB to cause insulin resistance, the IKK inhibitors acetylsalicylate and parthenolide prevented FA-induced reductions in insulin-stimulated glucose uptake and NFB nuclear translocation. Most importantly, NFB SN50, a cell-permeable peptide that inhibits NFB nuclear translocation downstream of IKK, was sufficient to prevent palmitate-induced reductions in insulin-stimulated glucose uptake. Acetylsalicylate, but not NFB SN50, prevented FA effects on phosphatidylinositol-3 kinase activity and protein kinase B phosphorylation. We conclude that FAs induce insulin resistance and activates NFB in L6 cells. Furthermore, inhibition of NFB activation, indirectly by preventing IKK activation or directly by inhibiting NFB nuclear translocation, prevents the detrimental effects of palmitate on the metabolic actions of insulin in L6 myotubes.Insulin resistance is a hallmark of obesity/type 2 diabetes. Although the pathogenesis of insulin resistance is poorly understood, dyslipidemia has been proposed as a candidate mechanism. Supporting this hypothesis are observations that plasma and tissue lipid levels are inversely correlated with insulin sensitivity (1, 2), that reduced availability of lipids improves insulin sensitivity (3-6), that a short-term lipid/ fatty acid infusion can induce insulin resistance (6 -11), and that lipid metabolites such as diacylglycerol and ceramide can inhibit insulin signaling (6,(12)(13)(14)(15). More recent in vivo and in vitro studies have implicated inhibitor of B kinase (IKK) 1 in mediating the detrimental effects of lipids on insulin action (11, 16 -18). Thus, inhibition of IKK activity by salicylates prevents the development of skeletal muscle insulin resistance caused by short-term lipid infusions in rats and mice (17) and improves insulin sensitivity in type 2 diabetes (16), and IKK heterozygote knockout mice are resistant to the development of insulin resistance induced by a high fat diet or a lipid infusion (18). However, the mechanism(s) by which increased IKK activity mediates lipid-induced insulin resistance are poorly understood.IKK is a serine kinase identified as a proximal element of the pro-inflammatory IKK/IB/NFB pathway (19,20). Activated IKK phosphorylates inhibitor of B (IB), a cytoplasmic protein that i...

Glioblastoma is the most common primary malignant brain tumour. Survival is poor and improved treatment options are urgently needed. Although immunotherapies have emerged as effective treatments for a number of cancers, translation of these through to brain tumours is a distinct challenge, particularly due to the blood–brain barrier and the unique immune tumour microenvironment afforded by CNS-specific cells. This review discusses the immune system within the CNS, mechanisms of immune escape employed by glioblastoma, and the immunological effects of conventional glioblastoma treatments. Novel therapies for glioblastoma that harness the immune system and their current clinical progress are outlined, including cancer vaccines, T-cell therapies and immune checkpoint modulators.

Stefanovic-Racic M, Perdomo G, Mantell BS, Sipula IJ, Brown NF, O'Doherty RM. A moderate increase in carnitine palmitoyltransferase 1a activity is sufficient to substantially reduce hepatic triglyceride levels. Am J Physiol Endocrinol Metab 294: E969-E977, 2008. First published March 18, 2008 doi:10.1152/ajpendo.00497.2007.-Nonalcoholic fatty liver disease (NAFLD), hypertriglyceridemia, and elevated free fatty acids are present in the majority of patients with metabolic syndrome and type 2 diabetes mellitus and are strongly associated with hepatic insulin resistance. In the current study, we tested the hypothesis that an increased rate of fatty acid oxidation in liver would prevent the potentially harmful effects of fatty acid elevation, including hepatic triglyceride (TG) accumulation and elevated TG secretion. Primary rat hepatocytes were transduced with adenovirus encoding carnitine palmitoyltransferase 1a (Adv-CPT-1a) or control adenoviruses encoding either ␤-galactosidase (Adv-␤-gal) or carnitine palmitoyltransferase 2 (Adv-CPT-2). Overexpression of CPT-1a increased the rate of ␤-oxidation and ketogenesis by ϳ70%, whereas esterification of exogenous fatty acids and de novo lipogenesis were unchanged. Importantly, CPT-1a overexpression was accompanied by a 35% reduction in TG accumulation and a 60% decrease in TG secretion by hepatocytes. There were no changes in secretion of apolipoprotein B (apoB), suggesting the synthesis of smaller, less atherogenic VLDL particles. To evaluate the effect of increasing hepatic CPT-1a activity in vivo, we injected lean or obese male rats with Adv-CPT-1a, Adv-␤-gal, or Adv-CPT-2. Hepatic CPT-1a activity was increased by ϳ46%, and the rate of fatty acid oxidation was increased by ϳ44% in lean and ϳ36% in obese CPT-1a-overexpressing animals compared with Adv-CPT-2-or Adv-␤-gal-treated rats. Similar to observations in vitro, liver TG content was reduced by ϳ37% (lean) and ϳ69% (obese) by this in vivo intervention. We conclude that a moderate stimulation of fatty acid oxidation achieved by an increase in CPT-1a activity is sufficient to substantially reduce hepatic TG accumulation both in vitro and in vivo. Therefore, interventions that increase CPT-1a activity could have potential benefits in the treatment of NAFLD. fatty liver NONALCOHOLIC FATTY LIVER DISEASE (NAFLD) represents a spectrum of liver abnormalities with an estimated prevalence between 14 and 24% in the general population (4). Furthermore, NAFLD is present in the majority of patients with metabolic syndrome and type 2 diabetes mellitus (DM) (29) and is strongly associated with insulin resistance (38) characterized by the inability of insulin to control hepatic gluconeogenesis (28). Although most patients with NAFLD have asymptomatic fatty liver, the condition predisposes toward the development of steatohepatitis, cirrhosis, and hepatocellular carcinoma. Furthermore, hepatic lipid accumulation is associated with a more atherogenic lipid profile (25), including hypertriglyceridemia, a higher plasma concentration of...

Skeletal muscle insulin resistance may be aggravated by intramyocellular accumulation of fatty acid-derived metabolites that inhibit insulin signaling. We tested the hypothesis that enhanced fatty acid oxidation in myocytes should protect against fatty acid-induced insulin resistance by limiting lipid accumulation. L6 myotubes were transduced with adenoviruses encoding carnitine palmitoyltransferase I (CPT I) isoforms or ␤-galactosidase (control). Two to 3-fold overexpression of L-CPT I, the endogenous isoform in L6 cells, proportionally increased oxidation of the long-chain fatty acids palmitate and oleate and increased insulin stimulation of [ Insulin resistance in skeletal muscle is frequently present in obesity and is an early characteristic of the development of type 2 diabetes mellitus. Consistent with the association between insulin resistance and obesity, multiple lines of inquiry suggest a close relationship between the development of disease and disordered lipid metabolism. In particular, in both rodent (1, 2) and human (3-6) studies, a correlation has been observed between the degree of insulin resistance in vivo and the triacylglycerol content of muscle cells, the primary target for insulin-stimulated glucose disposal. A possible causal relationship has been proposed in which the high plasma fatty acid levels frequently observed in the obese/insulin-resistant state drive muscle lipid accumulation that in turn causes a predisposition toward decreased insulin sensitivity and worsening of the disease, the so-called "lipotoxic" model of skeletal muscle insulin resistance. Evidence for this hypothesis comes from a series of in vivo model systems in which artificial elevations in plasma fatty acid levels over several hours induced lipid build-up and insulin resistance in muscle tissue (7-10). Parallel observations have been made in vitro in which incubation of model muscle cells in tissue culture with fatty acids has analogous consequences (11-13).Although the association between increased intramyocellular lipid and the development of insulin resistance is compelling, the mechanism of the effect is far from clear. For example, triacylglycerol accumulation in muscle cells is not invariably associated with insulin resistance. Notably the muscle of trained endurance athletes has been shown to be highly insulin-sensitive despite the presence of high levels of intramyocellular triacylglycerol (14), and shorter term (4-week) exercise training in humans appears to improve muscle insulin sensitivity in the absence of measurable changes in muscle triacylglycerol content (15). To account for this apparent discrepancy, it has been proposed that triglyceride accumulation within insulin-resistant muscle is merely a marker for some other harmful fatty acid-derived metabolite(s). In particular, diacylglycerol (16), ceramide (17), and long-chain acyl-CoA (18) are also elevated in certain insulin-resistant muscle models. Each of these has been implicated in mediating the negative effects of lipids on insulin signaling via ...

The expression pattern of mitochondrial carnitine palmitoyltransferase (CPT) enzymes was examined in the developing rat heart. Whereas the specific activity of CPT II increased approximately 3-fold during the first month of life, the profile for CPT I, which is composed of both liver (L) and muscle (M) isoforms, was more complex. Exposure of mitochondria to [3H]etomoxir (a covalent ligand for CPT I), followed by fluorographic analysis of the membrane proteins, established that while in the adult heart L-CPT I represents a very minor constituent, its contribution is much greater in the newborn animal. Use of the related inhibitor, 2-[6-(2,4-dinitrophenoxy)hexyl]oxirane-2-carboxylic acid (specific for L-CPT I), allowed the activities of the two CPT I variants to be quantified separately. The results showed that in the neonatal heart, L-CPT I contributes approximately 25% to total CPT I activity (in Vmax terms), the value falling during growth of the pups (with concomitant increasing expression of the M isoform) to its adult level of 2-3%. Because the myocardial carnitine content is very low at birth and rises dramatically over the next several weeks, it can be estimated that L-CPT I (Km for carnitine of only 30 microM compared with a value of 500 microM for M-CPT I) is responsible for some 60% of total cardiac fatty acid oxidation in the newborn rat; the value falls to approximately 4% in adult animals. Should these findings have a parallel in humans, they could have important implications for understanding the pathophysiological consequences of inherited L-CPT I deficiency syndromes.

We set out to determine if the cDNA encoding a carnitine palmitoyltransferase (CPT)-like protein recently isolated from rat brown adipose tissue (BAT) by Yamazaki et al. (Yamazaki, N., Shinohara, Y., Shima, A., and Terada, H. (1995) FEBS Lett. 363, 41-45) actually encodes the muscle isoform of mitochondrial CPT I (M-CPT I). To this end, a cDNA essentially identical to the original BAT clone was isolated from a rat heart library. When expressed in COS cells, the novel cDNA and our previously described cDNA for rat liver CPT I (L-CPT I) gave rise to products with the same kinetic characteristics (sensitivity to malonyl-CoA and Km for carnitine) as CPT I in skeletal muscle and liver mitochondria, respectively. When labeled with [3H]etomoxir, recombinant L-CPT I and putative M-CPT I, although having approximately the same predicated masses (88.2 kDa), migrated differently on SDS gels, as did CPT I from liver and muscle mitochondria. The same was true for the products of in vitro transcription and translation of the L-CPT I and putative M-CPT I cDNAs. We conclude that the BAT cDNA does in fact encode M-CPT I. Northern blots using L- and M-CPT I cDNA probes revealed the presence of L-CPT I mRNA in liver and heart and its absence from skeletal muscle and BAT. M-CPT I mRNA, which was absent from liver, was readily detected in skeletal muscle and was particularly strong in heart and BAT. Whereas the signal for L-CPT I was more abundant than that for M-CPT I in RNA isolated from whole epididymal fat pad, this was reversed in purified adipocytes from this source. These findings, coupled with the kinetic properties and migration profiles on SDS gels of CPT I in brown and white adipocytes, indicate that the muscle form of the enzyme is the dominant, if not exclusive, species in both cell types.

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