Identification of three novel pathogenic mutations in cystathionine beta-synthase gene of Pakistani intellectually disabled patients

BACKGROUND

Classical homocystinuria (HCU) is an autosomal recessive inborn error of metabolism, which is caused by the cystathionine-β-synthase (CBS: encoded by CBS) deficiency. Symptoms of untreated classical HCU patients include intellectual disability (ID), ectopia lentis and long limbs, along with elevated plasma methionine, and homocysteine.

METHODS

A total of 429 ID patients (age range: 1.6-23 years) were sampled from Northern areas of Punjab, Pakistan. Biochemical and genetic analyses were performed to find classical HCU disease in ID patients.

RESULTS

Biochemically, nine patients from seven unrelated families were identified with high levels of plasma methionine and homocysteine. Targeted exonic analysis of CBS confirmed seven causative homozygous mutations; of which three were novel missense mutations (c.451G>T; p.Gly151Trp, c.975G>C; p.Lys325Asn and c.1039 + 1G>T splicing), and four were recurrent variants (c.451 + 1G>A; IVS4 + 1 splicing, c.770C>T; p.Thr257Met, c.808_810del GAG; p.Glu270del and c.752T>C; p.Leu251Pro). Treatment of patients was initiated without further delay with pyridoxine, folic acid, cobalamin, and betaine as well as dietary protein restriction. The immediate impact was noticed in behavioral improvement, decreased irritability, improved black hair color, and socialization. Overall, health outcomes in this disorder depend on the age and symptomatology at the time of treatment initiation.

CONCLUSIONS

With personalized treatment and care, such patients can reach their full potential of living as healthy a life as possible. This screening study is one of the pioneering initiatives in Pakistan which would help to minimize the burden of such treatable inborn errors of metabolism in the intellectually disabled patients.

Central role of c-Src in NOX5- mediated redox signalling in vascular smooth muscle cells in human hypertension

AIMS

NOX-derived reactive oxygen species (ROS) are mediators of signalling pathways implicated in vascular smooth muscle cell (VSMC) dysfunction in hypertension. Among the numerous redox-sensitive kinases important in VSMC regulation is c-Src. However, mechanisms linking NOX/ROS to c-Src are unclear, especially in the context of oxidative stress in hypertension. Here, we investigated the role of NOX-induced oxidative stress in VSMCs in human hypertension focusing on NOX5, and explored c-Src, as a putative intermediate connecting NOX5-ROS to downstream effector targets underlying VSMC dysfunction.

METHODS AND RESULTS

VSMC from arteries from normotensive (NT) and hypertensive (HT) subjects were studied. NOX1,2,4,5 expression, ROS generation, oxidation/phosphorylation of signalling molecules, and actin polymerization and migration were assessed in the absence and presence of NOX5 (melittin) and Src (PP2) inhibitors. NOX5 and p22phox-dependent NOXs (NOX1-4) were down-regulated using NOX5 siRNA and p22phox-siRNA approaches. As proof of concept in intact vessels, vascular function was assessed by myography in transgenic mice expressing human NOX5 in a VSMC-specific manner. In HT VSMCs, NOX5 was up-regulated, with associated oxidative stress, hyperoxidation (c-Src, peroxiredoxin, DJ-1), and hyperphosphorylation (c-Src, PKC, ERK1/2, MLC20) of signalling molecules. NOX5 siRNA reduced ROS generation in NT and HT subjects. NOX5 siRNA, but not p22phox-siRNA, blunted c-Src phosphorylation in HT VSMCs. NOX5 siRNA reduced phosphorylation of MLC20 and FAK in NT and HT. In p22phox- silenced HT VSMCs, Ang II-induced phosphorylation of MLC20 was increased, effects blocked by melittin and PP2. NOX5 and c-Src inhibition attenuated actin polymerization and migration in HT VSMCs. In NOX5 transgenic mice, vascular hypercontractilty was decreased by melittin and PP2.

CONCLUSION

We define NOX5/ROS/c-Src as a novel feedforward signalling network in human VSMCs. Amplification of this system in hypertension contributes to VSMC dysfunction. Dampening the NOX5/ROS/c-Src pathway may ameliorate hypertension-associated vascular injury.

Abstract 068: Interplay Between Nox5 and Endoplasmic Reticulum Stress Regulates Vascular Signalling in Human Hypertension

Nox5, a major ROS-generating oxidase in human vessels, regulates vascular contraction. We demonstrated an ER-perinuclear Nox5 localization and questioned the role of ER stress in Nox5 regulation. Vascular smooth muscle cells (VSMC) were isolated from small arteries from subcutaneous fat from normotensive (NT) and hypertensive (HT) subjects. Nox5 compartmentalization (cell fractionation); ROS generation (chemiluminescence); peroxiredoxin/DJ-1 oxidation, activation of ER stress and contractile signalling (IRE1α, Src, PKC, MLC phosphorylation; immunoblotting) and actin cytoskeleton organization (phalloidin staining) were assessed. In hypertension, ROS levels (139±27% vs NT, p<0.05), oxidation of peroxiredoxin (870.4±188.7% vs NT, p<0.05) and DJ-1 (125±34% vs NT, p<0.05) were increased. IRE1α phosphorylation was increased in the HT group (58±21% vs NT, p<0.05). ER stress inhibition (4-PBA, 1mM) reduced ROS levels in HT subjects (20±6% vs NT, p<0.05), suggesting association between ER and oxidative stress. Nox5 expression was increased in the HT group (103±23% vs NT, p<0.05) in a compartment specific manner: Nox5 levels were reduced in plasma membrane (45±7% vs NT, p<0.05), but increased in the ER/nuclear fraction (46±13% vs NT, p<0.05). IRE1 inhibition (STF083010, 60μM) decreased Nox5 expression in the HT group (65±5% vs Ctl, p<0.05), while induction of ER stress (tunicamycin, 5μg/ml, 24h) increased Nox5 expression in cells from both groups (p<0.05). To investigate the role of Nox5 on contractile signalling, cells were treated with mellitin (100nM), a Nox5 inhibitor. ROS generation and phosphorylation of c-Src, PKC and MLC 20 induced by Ang II were reduced by mellitin in both groups (p<0.05 vs Ctl). In contrast, silencing of p22phox increased ROS and activation of c-Src, PKC and MLC 20 in both groups, an effect blocked by mellitin (p<0.05 vs Ctl). VSMC from hypertensive subjects had increased number of stress fibres, an effect attenuated by mellitin. Our findings demonstrate that Nox5 is upregulated in a compartment specific manner and is regulated by ER stress in hypertension. Nox5 upregulation influences pro-contractile signalling and cytoskeleton reorganization in VSMC, processes that contribute to vascular dysfunction in hypertension.

Imbalance between neutrophil elastase and its inhibitor α1-antitrypsin in obesity alters insulin sensitivity, inflammation, and energy expenditure

The molecular mechanisms involved in the development of obesity and related complications remain unclear. Here, we report that obese mice and human subjects have increased activity of neutrophil elastase (NE) and decreased serum levels of the NE inhibitor α1-antitrypsin (A1AT, SerpinA1). NE null (Ela2(-/-)) mice and A1AT transgenic mice were resistant to high-fat diet (HFD)-induced body weight gain, insulin resistance, inflammation, and fatty liver. NE inhibitor GW311616A reversed insulin resistance and body weight gain in HFD-fed mice. Ela2(-/-) mice also augmented circulating high molecular weight (HMW) adiponectin levels, phosphorylation of AMP-activated protein kinase (AMPK), and fatty acid oxidation (FAO) in the liver and brown adipose tissue (BAT) and uncoupling protein (UCP1) levels in the BAT. These data suggest that the A1AT-NE system regulates AMPK signaling, FAO, and energy expenditure. The imbalance between A1AT and NE contributes to the development of obesity and related inflammation, insulin resistance, and liver steatosis.

Identification of hepatitis B virus core mutants by PCR-RFLP in chronic hepatitis B patients from Punjab, Pakistan

Chronic hepatitis B virus (HBV) infection remains a major health issue worldwide. Several factors including core gene variation are responsible for the development of chronicity of HBV infection. The present study was designed to identify the variations in the core region of the HBV genome in a local population of chronic hepatitis B patients (n = 57) using a PCR-based restriction fragment length polymorphism (PCR-RFLP) method. Fifty subjects were found to be positive for the presence of HBV DNA. For the core region genotyping, the Ava II and Msp I restriction enzymes were used. Mutations at nucleotide (nt) 2147 and nt 2362 in the HBV genome in the core region for Ava II (A4 type, 74%) and nt 2331 for Msp I (M1 type, 66%) were observed as the most common pattern. These results are different from those of previously reported studies on other populations and thus appear to be unique to the Pakistani population. This type of characterization of core mutants may be useful for the design of vaccines based on viral epitopes that are effective for the Pakistani population. Moreover, these unique genotypic patterns for the HBV core gene might be some of the main factors responsible for understanding the underlying mechanism by which HBV chronicity is developed in the Pakistani population.

MRS reveals additional hexose N-acetyl resonances in the brain of a mouse model for Sandhoff disease

Sandhoff disease, one of several related lysosomal storage disorders, results from the build up of N-acetyl-containing glycosphingolipids in the brain and is caused by mutations in the genes encoding the hexosaminidase beta-subunit. Affected individuals undergo progressive neurodegeneration in response to the glycosphingolipid storage. (1)H magnetic resonance spectra of perchloric acid extracts of Sandhoff mouse brain exhibited several resonances ca 2.07 ppm that were not present in the corresponding spectra from extracts of wild-type mouse brain. High-performance liquid chromatography and mass spectrometry of the Sandhoff extracts post-MRS identified the presence of N-acetylhexosamine-containing oligosaccharides, which are the likely cause of the additional MRS resonances. MRS of intact brain tissue with magic angle spinning also showed additional resonances at ca 2.07 ppm in the Sandhoff case. These resonances appeared to increase with disease progression and probably arise, for the most part, from the stored glycosphingolipids, which are absent in the aqueous extracts. Hence in vivo MRS may be a useful tool for detecting early-stage Sandhoff disease and response to treatment.