Phong Nguyen

Liver-specific Knockdown of JNK1 Up-regulates Proliferator-activated Receptor γ Coactivator 1β and Increases Plasma Triglyceride despite Reduced Glucose and Insulin Levels in Diet-induced Obese Mice

The c-Jun N-terminal kinases (JNKs) have been implicated in the development of insulin resistance, diabetes, and obesity. Genetic disruption of JNK1, but not JNK2, improves insulin sensitivity in diet-induced obese (DIO) mice. We applied RNA interference to investigate the specific role of hepatic JNK1 in contributing to insulin resistance in DIO mice. Adenovirus-mediated delivery of JNK1 short-hairpin RNA (Ad-shJNK1) resulted in almost complete knockdown of hepatic JNK1 protein without affecting JNK1 protein in other tissues. Liver-specific knockdown of JNK1 resulted in significant reductions in circulating insulin and glucose levels, by 57 and 16%, respectively. At the molecular level, JNK1 knockdown mice had sustained and significant increase of hepatic Akt phosphorylation. Furthermore, knockdown of JNK1 enhanced insulin signaling in vitro. Unexpectedly, plasma triglyceride levels were robustly elevated upon hepatic JNK1 knockdown. Concomitantly, expression of proliferator-activated receptor γ coactivator 1β, glucokinase, and microsomal triacylglycerol transfer protein was increased. Further gene expression analysis demonstrated that knockdown of JNK1 up-regulates the hepatic expression of clusters of genes in glycolysis and several genes in triglyceride synthesis pathways. Our results demonstrate that liver-specific knockdown of JNK1 lowers circulating glucose and insulin levels but increases triglyceride levels in DIO mice.

A new spin on an old model : In vivo evaluation of disease progression by magnetic resonance imaging with respect to standard inflammatory parameters and histopathology in the adjuvant arthritic rat

OBJECTIVE To noninvasively examine the pathogenesis of rat adjuvant-induced arthritis (AIA) by magnetic resonance imaging (MRI), and to correlate MRI indices of disease progression with classic inflammatory parameters and histologic evaluation. METHODS AIA was established in male Lewis rats following subcutaneous injection in the right hindpaw with 0.5 mg of heat-killed Mycobacterium butyricum suspended in light mineral oil. In vivo MRI evaluations of soft tissue and bony changes in AIA rats with matched histopathology were correlated with changes in left hindpaw volumes, circulating leukocytes, acute-phase reactants, and urinary collagen crosslinks throughout the disease process. RESULTS MRI of arthritic tibiotarsal joints of the uninjected left hindpaws from AIA rats demonstrated 2 distinct phases of disease activity. The first phase, apparent between days 10 and 18, was characterized by periarticular inflammation with marked synovitis, synovial fibroplasia, and distension of the joint capsule into the surrounding tissue. The secondary phase, occurring between days 18 and 30, was marked by continued soft tissue inflammation, periostitis with osteolysis, and periosteal new bone formation progressing to a state of near complete ankylosis by day 30. These 2 phases of disease activity observed by MRI paralleled biochemical, cellular, and histologic markers of disease progression. CONCLUSION MRI can be used to noninvasively detect, monitor, and quantify the chronic synovitis and progressive destruction of soft tissue and bone in live AIA rats, thereby improving the ability to evaluate disease progression in this preclinical animal model of rheumatoid arthritis.

Pharmacology of 2-[4-(4-Chloro-2-fluorophenoxy)phenyl]-pyrimidine-4-carboxamide: A Potent, Broad-Spectrum State-Dependent Sodium Channel Blocker for Treating Pain States

Voltage-gated Na+ channels may play important roles in establishing pathological neuronal hyperexcitability associated with chronic pain in humans. Na+ channel blockers, such as carbamazepine (CBZ) and lamotrigine (LTG), are efficacious in treating neuropathic pain; however, their therapeutic utility is compromised by central nervous system side effects. We reasoned that it may be possible to gain superior control over pain states and, in particular, a better therapeutic index, by designing broad-spectrum Na+ channel blockers with higher potency, faster onset kinetics, and greater levels of state dependence than existing drugs. 2-[4-(4-Chloro-2-fluorophenoxy)phenyl]-pyrimidine-4-carboxamide (PPPA) is a novel structural analog of the state-dependent Na+ channel blocker V102862 [4-(4-fluorophenoxy)benzaldehyde semicarbazone]. Tested on recombinant rat Nav1.2 channels and native Na+ currents in cultured rat dorsal root ganglion neurons, PPPA was approximately 1000 times more potent, had 2000-fold faster binding kinetics, and ≥10-fold higher levels of state dependence than CBZ and LTG. Tested in rat pain models against mechanical endpoints, PPPA had minimal effective doses of 1 to 3 mg/kg p.o. in partial sciatic nerve ligation, Freunds complete adjuvant, and postincisional pain. In all cases, efficacy was similar to clinically relevant comparators. Importantly, PPPA did not produce motor deficits in the accelerating Rotarod assay of ataxia at doses up to 30 mg/kg p.o., indicating a therapeutic index >10, which was superior to CBZ and LTG. Our experiments suggest that high-potency, broad-spectrum, state-dependent Na+ channel blockers will have clinical utility for treating neuropathic, inflammatory, and postsurgical pain. Optimizing the biophysical parameters of broad-spectrum voltage-gated Na+ channel blockers may lead to improved pain therapeutics.

Hepatic knockdown of stearoyl-COA desaturase 1 via RNA interference in obese mice decreases lipid content and changes fatty acid composition

Stearoyl-CoA desaturases (SCDs) catalyze the biosynthesis of monounsaturated fatty acids from saturated fatty acids. Four scd genes have been identified in mice and three in human (including one pseudogene). Among the four mouse SCD isoforms, SCD1 is predominantly expressed in liver and adipose tissue. Mice null for the scd1 gene have reduced adiposity, increased energy expenditure and altered lipid profiles. To further evaluate the specific role of hepatic SCD1 and the potential to achieve similar desirable phenotypic changes in adult obese mice, adenovirus-mediated short hairpin interfering RNA (shRNA) was used to acutely knock down hepatic scd1 expression in ob/ob mice. Robust reductions in hepatic SCD1 mRNA and SCD1 enzymatic activity were achieved, sustained up to 2 weeks. Reduced hepatic content of neutral lipids and robust lowering of lipid desaturation indexes, but increased content of liver phosphotidylcholine were observed with SCD1 knockdown. Increased total plasma cholesterol levels were also observed. No significant changes in body weight were observed. Expression levels of several lipogenic and lipid oxidation genes were not significantly altered by short term SCD1 reduction, but UCP2 expression was increased. Our results demonstrate that significant changes to both hepatic and systemic lipid profiles can be achieved through specific knockdown of liver-expressed SCD1 in the ob/ob mouse model. However, hepatic SCD1 knockdown does not result in significant changes in body weight in the short term.