CBS-deficient Mice Research Articles

Abnormal Amino Acid Profiles of Blood and Cerebrospinal Fluid from Cystathionine β-Synthase-Deficient Mice, an Animal Model of Homocystinuria.

Mental retardation is the most common feature among inborn errors of amino acid metabolism. Patients with homocystinuria/homocysteinemia caused by cystathionine β-synthase (CBS) deficiency suffer from thromboembolism and mental retardation from early ages; therefore, detection by newborn screening is performed. Furthermore, elevated levels of serum homocysteine during pregnancy are associated with the occurrence of neural tube defects (NTDs) in newborns. However, the causes of such central nervous system (CNS) defects are unknown. We found previously impaired learning abilities in Cbs-deficient (Cbs-/-) mice (but not NTD births). Here, we investigated the amino acid profiles of serum and cerebrospinal fluid (CSF) from Cbs-/- mice. Mice deficient in cystathionine γ-lyase (Cth), a downstream enzyme of CBS in transsulfuration, as well as wild-type mice, were analyzed as controls. Cbs-/- and Cth-/- mice were smaller than wild-type mice, and CSF yields in Cbs-/- mice were lower than the others. CSF amino acid levels were generally lower than those in serum, and compared with the dramatic amino acid level alterations in Cbs-/- mouse serum, alterations in CSF were less apparent. However, marked upregulation (versus wild-type) of aspartic acid/asparagine (Asp/Asn), glutamine (Gln), serine (Ser), threonine (Thr), phenylalanine (Phe), tyrosine (Tyr), methionine (Met), total homocysteine, and citrulline, and downregulation of lysine (Lys) were found in Cbs-/- mouse CSF. Because similar regulation of total homocysteine/citrulline/Lys was observed in the CSF of Cth-/- mice, which are free of CNS dysfunction, the reduced CSF volumes and the level changes of other amino acids could be relevant to Cbs-/--specific CNS defects.

Hydrogen Sulfide Promotes Bone Homeostasis by Balancing Inflammatory Cytokine Signaling in CBS-Deficient Mice through an Epigenetic Mechanism

Previously, we have shown hyperhomocysteinemia (HHcy) to have a detrimental effect on bone remodeling, which is associated with osteoporosis. During transsulfuration, Hcy is metabolized into hydrogen sulfide (H2S), a gasotransmitter molecule known to regulate bone formation. Therefore, in the present study, we examined whether H2S ameliorates HHcy induced epigenetic and molecular alterations leading to osteoporotic bone loss. To test this mechanism, we employed cystathionine-beta-synthase heterozygote knockout mice, fed with a methionine rich diet (CBS+/− +Met), supplemented with H2S-donor NaHS for 8 weeks. Treatment with NaHS, normalizes plasma H2S, and completely prevents trabecular bone loss in CBS+/− mice. Our data showed that HHcy caused inhibition of HDAC3 activity and subsequent inflammation by imbalancing redox homeostasis. The mechanistic study revealed that inflammatory cytokines (IL-6, TNF-α) are transcriptionally activated by an acetylated lysine residue in histone (H3K27ac) of chromatin by binding to its promoter and subsequently regulating gene expression. A blockade of HDAC3 inhibition in CBS+/− mice by HDAC activator ITSA-1, led to the remodeling of histone landscapes in the genome and thereby attenuated histone acetylation-dependent inflammatory signaling. We also confirmed that RUNX2 was sulfhydrated by administration of NaHS. Collectively, restoration of H2S may provide a novel treatment for CBS-deficiency induced metabolic osteoporosis.

Circular RNAs profiling in the cystathionine-β-synthase mutant mouse reveals novel gene targets for hyperhomocysteinemia induced ocular disorders

Cystathionine-β-synthase (CBS) gene encodes L-serine hydrolyase which catalyzes β-reaction to condense serine with homocysteine (Hcy) by pyridoxal-5′-phosphate helps to form cystathionine which in turn is converted to cysteine. CBS resides at the intersection of transmethylation, transsulfuration, and remethylation pathways, thus lack of CBS fundamentally blocks Hcy degradation; an essential step in glutathione synthesis. Redox homeostasis, free-radical detoxification and one-carbon metabolism (Methionine-Hcy-Folate cycle) require CBS and its deficiency leads to hyperhomocysteinemia (HHcy) causing retinovascular thromboembolism and eye-lens dislocation along with vascular cognitive impairment and dementia. HHcy results in retinovascular, coronary, cerebral and peripheral vessels' dysfunction and how it causes metabolic dysregulation predisposing patients to serious eye conditions remains unknown. HHcy orchestrates inflammation and redox imbalance via epigenetic remodeling leading to neurovascular pathologies. Although circular RNAs (circRNAs) are dominant players regulating their parental genes' expression dynamics, their importance in ocular biology has not been appreciated. Progress in gene-centered analytics via improved microarray and bioinformatics are enabling dissection of genomic pathways however there is an acute under-representation of circular RNAs in ocular disorders. This study undertook circRNAs' analysis in the eyes of CBS deficient mice identifying a pool of 12532 circRNAs, 74 exhibited differential expression profile, ∼27% were down-regulated while most were up-regulated (∼73%). Findings also revealed several microRNAs that are specific to each circRNA suggesting their roles in HHcy induced ocular disorders. Further analysis of circRNAs helped identify novel parental genes that seem to influence certain eye disease phenotypes.

Hydrogen Sulfide As a Potential Target in Preventing Spermatogenic Failure and Testicular Dysfunction.

Testis and sperm are particularly susceptible to inflammation and oxidative stress. Although hydrogen sulfide (H2S) has been considered an important biological signaling molecule in inflammatory and oxidative stress processes, its role in the male reproductive system was poorly understood. The aim of this study was to investigate the role of H2S in the regulation of male reproductive system. We found that both subfertile and infertile patients, especially asthenospermic patients, exhibited decreased concentration of H2S in their seminal plasma and diminished expression of H2S-generating enzyme (cystathionine β-synthase [CBS]) in sperm. Supplying exogenous H2S to semen improved sperm motility of these asthenospermic patients. Furthermore, decreased sperm motility was observed in animal models with a defective in H2S generation such as lipopolysaccharide-treated mice, diabetic mice, and CBS-deficient mice. Our research showed that stress-induced reductions of endogenous H2S production and CBS expression are correlated with impaired spermatogenesis and a defective blood-testis barrier. Supplying exogenous H2S or overexpressing CBS could relieve the spermatogenic failure. This occurred primarily through the combination of anti-inflammatory and antioxidative effects. These results provide the first indication that H2S is important for maintaining male fertility and protecting testicular function. H2S plays an important role in spermatogenic failure and testicular dysfunction mainly by its anti-inflammatory and antioxidative effects. Antioxid. Redox Signal. 28, 1447-1462.

Mesenchymal Stem Cells Derived Exosomes Promotes Bone Regeneration through Cystathionine‐β‐synthase Enhanced Angiogenesis and Osteogenesis during Bone Development

It is critical that bone formation and angiogenesis are tightly coordinated during bone development and fracture healing, but the molecular regulator of such intercellular communication in bone microenvironment are not well studied. Cystathionine‐β‐synthase (CBS), an enzyme in homocysteine (Hcy) metabolic pathway play crucial role in osteoblast differentiation. Therefore, we hypothesize that CBS as a novel molecular regulator in osteoblasts, which regulates vascularization during bone development in osteoblast derived exosome. To test this hypothesis, we have used 7–10 weeks old male mice in our study; wild type mice (C57BL/6, WT) and CBS+/− mice. Blocking the CBS function was done by either inhibitor hydroxylamine (HA) or SiRNA prevented osteoblast differentiation and mineralization. This was supported by studies using osteoblasts cultured from bone marrow of CBS deficient (CBS+/−) mice. Exosomes of mesenchymal stem cell derived osteoblasts cultured stimulated endothelial migration and angiogenesis, which was prevented by blocking CBS in osteoblasts using HA or SiRNA. Mass spectrometry analysis and ELISA assay identified among others vascular endothelial growth factor (VEGF)‐A and VEGF homolog placental growth factor (PIGF) to be present in control osteoblasts culture medium and CBS(+/+) mice osteoblasts but not in osteoblasts treated with HA and CBS+/− osteoblasts. Immunostaining and metatarsal angiogenesis assay showed retarded vascularization in bone tissue of CBS+/− mice. However, osteopenia phenotype was confirmed in CBS+/− mice by microCT analysis. CBS+/− mice showed significantly reduced bone mineral density (BMD) and bone volume/tissue volume (BV/TV) and showed increased plasma Hcy levels compared to CBC+/+ mice (WT). However, CBS+/− mice exhibited a more significant increase in the number of TRAP‐positive osteoclasts and higher levels of RANKL than CBS+/+ mice. This suggests that Hcy levels may be associated with osteoclast activity. Furthermore, real‐time PCR and western blot analyses revealed significant decreases Alkaline phosphatase (ALP) and Runt‐related transcription factor 2 (RUNX2) expression in CBS‐deficient (CBS+/−) mouse bone marrow cells. In conclusion, we demonstrate that CBS in osteoblasts is at the crossroad of osteoblast differentiation/mineralization and angiogenesis. These findings uncover the previously undefined molecular understanding of CBS that promote angiogenesis and osteogenesis in bone development and fracture repair.Support or Funding InformationThis work is financial supported from National Institute of health grant AR‐067667 and HL‐107640‐NT are greatly acknowledged.

Lack of global epigenetic methylation defects in CBS deficient mice.

Cystathionine β-synthase (CBS) deficiency is a recessive inborn error of metabolism in which patients have extremely elevated plasma total homocysteine and have clinical manifestations in the vascular, visual, skeletal, and nervous systems. Homocysteine is an intermediary metabolite produced from the hydrolysis of S-adenosylhomocysteine (SAH), which is a by-product of methylation reactions involving the methyl-donor S-adenosylmethionine (SAM). Here, we have measured SAM, SAH, DNA and histone methylation status in an inducible mouse model of CBS deficiency to test the hypothesis that homocysteine-related phenotypes are caused by inhibition of methylation due to elevated SAH and reduced SAM/SAH ratio. We found that mice lacking CBS have elevated cellular SAH and reduced SAM/SAH ratios in both liver and kidney, but this was not associated with alterations in the level of 5-methylcytosine or various histone modifications. Using methylated DNA immunoprecipitation in combination with microarray, we found that of the 241 most differentially methylated promoter probes, 89% were actually hypermethylated in CBS deficient mice. In addition, we did not find that changes in DNA methylation correlated well with changes in RNA expression in the livers of induced and uninduced CBS mice. Our data indicates that reduction in the SAM/SAH ratio, due to loss of CBS activity, does not result in overall hypomethylation of either DNA or histones.

Abstract 4785: Deficiency of cystathionine beta synthase gene does not affect tumor formation and survival of Eμ-myc mice

Abstract Aberrant DNA methylation is a hallmark of many types of cancers. S-adenosylhomocysteine (AdoHcy) is a strong inhibitor of DNA methytransferases. Deficiency of cystathionine beta synthase gene (Cbs) causes elevation of AdoHcy in variety of tissues. Here we have generated an Eμ-myc mouse model which is either wild type, heterozygous or homozygous for a deletion allele of Cbs (Eμ myc+ Cbs+/+; Eμ myc+ Cbs+/−; Eμ myc+ Cbs−/−). Homozygous Cbs deficient mice in both Eμ myc+ and Eμ myc− background were born at Mendelian frequency indicating that there is no synthetic lethality between Cbs and Eμ myc. In aging, we observed no significant difference in survival of Eμ myc+ Cbs+/+, Eμ myc+ Cbs+/− and Eμ myc+ Cbs−/− mice (Median survival of 150, 149 and 117 days respectively). However, preliminary data shows that tumor tissue from Eμ myc+ Cbs−/− animals has greatly elevated levels of AdoHcy compared to other genotypes. Our studies suggest that elevated levels of AdoHcy has no effect on tumor formation in Eμ myc mice. Citation Format: Sapna Gupta, Warren D. Kruger. Deficiency of cystathionine beta synthase gene does not affect tumor formation and survival of Eμ-myc mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4785. doi:10.1158/1538-7445.AM2015-4785

High homocysteine induces betaine depletion.

Betaine is the substrate of the liver- and kidney-specific betaine-homocysteine (Hcy) methyltransferase (BHMT), an alternate pathway for Hcy remethylation. We hypothesized that BHMT is a major pathway for homocysteine removal in cases of hyperhomocysteinaemia (HHcy). Therefore, we measured betaine in plasma and tissues from patients and animal models of HHcy of genetic and acquired cause. Plasma was collected from patients presenting HHcy without any Hcy interfering treatment. Plasma and tissues were collected from rat models of HHcy induced by diet and from a mouse model of cystathionine β-synthase (CBS) deficiency. S-adenosyl-methionine (AdoMet), S-adenosyl-homocysteine (AdoHcy), methionine, betaine and dimethylglycine (DMG) were quantified by ESI-LC-MS/MS. mRNA expression was quantified using quantitative real-time (QRT)-PCR. For all patients with diverse causes of HHcy, plasma betaine concentrations were below the normal values of our laboratory. In the diet-induced HHcy rat model, betaine was decreased in all tissues analysed (liver, brain, heart). In the mouse CBS deficiency model, betaine was decreased in plasma, liver, heart and brain, but was conserved in kidney. Surprisingly, BHMT expression and activity was decreased in liver. However, in kidney, BHMT and SLC6A12 expression was increased in CBS-deficient mice. Chronic HHcy, irrespective of its cause, induces betaine depletion in plasma and tissues (liver, brain and heart), indicating a global decrease in the body betaine pool. In kidney, betaine concentrations were not affected, possibly due to overexpression of the betaine transporter SLC6A12 where betaine may be conserved because of its crucial role as an osmolyte.

Molecular rescue of DYRK1A overexpression in cystathionine beta synthase-deficient mouse brain by enriched environment combined with voluntary exercise.

Hyperhomocysteinemia resulting from cystathionine beta synthase (CBS) deficiency can produce cognitive dysfunction. We recently found that CBS-deficient mice exhibit increased expression of the serine/threonine kinase dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A (DYRK1A) in the brain. When dysregulated, DYRK1A contributes to the neurodegeneration, neuronal death, and loss of function observed in neurodegenerative diseases. However, brain plasticity can be improved by interventions like enriched environment combined with voluntary exercise (EE/VE). The present study sought to assess the effects of EE/VE on molecular mechanisms linked to DYRK1A overexpression in the brain of CBS-deficient mice. EE/VE was applied to 3-month-old female CBS-deficient mice for 1 month. Without intervention, CBS-deficient mice exhibited increased DYRK1A and decreased brain-derived neurotrophic factor (BDNF) levels in the cortex and hippocampus. However, EE/VE rescued these altered DYRK1A and BDNF levels in the hippocampus of CBS-deficient mice. We conclude that exercise combined with enriched environment can restore the altered molecular mechanisms in the brain of CBS-deficient mice.

Protein arginine hypomethylation in a mouse model of cystathionine β‐synthase deficiency

Accumulation of the homocysteine (Hcy) precursor S-adenosylhomocysteine (AdoHcy) may cause cellular hypomethylation in the setting of hyperhomocysteinemia because of cystathionine β-synthase (CBS) deficiency, an inborn error of metabolism. To test this hypothesis, DNA and protein arginine methylation status were assessed in liver, brain, heart, and kidney obtained from a previously described mouse model of CBS deficiency. Metabolite levels in tissues and serum were determined by high-performance liquid chromatography or liquid chromatography-electrospray ionization-tandem mass spectrometry. Global DNA and protein arginine methylation status were evaluated as the contents of 5-methyldeoxycytidine in DNA and of methylarginines in proteins, respectively. In addition, histone arginine methylation was assessed by Western blotting. CBS-deficient mice exhibited increased (>6-fold) Hcy and AdoHcy levels in all tissues examined compared with control levels. In addition, global DNA methylation status was not affected, but global protein arginine methylation status was decreased (10-35%) in liver and brain. Moreover, asymmetric dimethylation of arginine 3 on histone H4 (H4R3me2a) content was markedly decreased in liver, and no differences were observed for the other histone arginine methylation marks examined. Our results show that CBS-deficient mice present severe accumulation of tissue Hcy and AdoHcy, protein arginine hypomethylation in liver and brain, and decreased H4R3me2a content in liver. Therefore, protein arginine hypomethylation arises as a potential player in the pathophysiology of CBS deficiency.

Dyrk1A, a Serine/Threonine Kinase, is Involved in ERK and Akt Activation in the Brain of Hyperhomocysteinemic Mice

Hyperhomocysteinemia due to cystathionine beta synthase (CBS) deficiency is associated with diverse brain disease. Whereas the biological actions linking hyperhomocysteinemia to the cognitive dysfunction are not well understood, we tried to establish relationships between hyperhomocysteinemia and alterations of signaling pathways. In the brain of CBS-deficient mice, a murine model of hyperhomocysteinemia, we previously found an activation of extracellular signal-regulated kinase (ERK) pathway and an increase of Dyrk1A, a serine/threonine kinase involved in diverse functions ranging from development and growth to apoptosis. We then investigated the relationship between Dyrk1A and the signaling pathways initiated by receptor tyrosine kinases (RTK), the ERK and PI3K/Akt pathways. We found a significant increase of phospho-ERK, phospho-MEK, and phospho-Akt in the brain of CBS-deficient and Dyrk1a-overexpressing mice. This increase was abolished when CBS-deficient and Dyrk1A-transgenic mice were treated with harmine, an inhibitor of Dyrk1A kinase activity, which emphasizes the role of Dyrk1A activity on ERK and Akt activation. Sprouty 2 protein level, a negative feedback loop modulator that limits the intensity and duration of RTK activation, is decreased in the brain of CBS-deficient mice, but not in the brain of Dyrk1A transgenic mice. Furthermore, a reduced Dyrk1A and Grb2 binding on sprouty 2 and an increased interaction of Dyrk1A with Grb2 were found in the brain of Dyrk1A transgenic mice. The consequence of Dyrk1A overexpression on RTK activation seems to be a decreased interaction of sprouty 2/Grb2. These observations demonstrate ERK and Akt activation induced by Dyrk1A in the brain of hyperhomocysteinemic mice and open new perspectives to understand the basis of the cognitive defects in hyperhomocysteinemia.

Cysteinemia, rather than homocysteinemia, is associated with plasma apolipoprotein A-I levels in hyperhomocysteinemia: Lipid metabolism in cystathionine β-synthase deficiency

ObjectiveGenetic and dietary hyperhomocysteinemia has been found to decrease high density lipoproteins (HDL) and their apolipoprotein A1 (APOA1). To test the hypothesis that the presence of cysteine could normalize HDL levels in hyperhomocysteinemic cystathionine β-synthase (Cbs)-deficient mice and that the inclusion of glycine would block this effect. MethodsLipids and HDL cholesterol were studied in Cbs-deficient mice and wild-type animals fed a low-methionine diet supplemented with cysteine and glycine and in Cbs-deficient mice on the same diet supplemented only with cysteine. ResultsTriglyceride and homocysteine levels were significantly decreased and increased, respectively in Cbs-deficient mice irrespective of treatment. However, plasma cholesterol, glucose and APOA1 were significantly decreased in homozygous Cbs-deficient mice when they received the cysteine and glycine-enriched beverage. This group of mice also showed decreased mRNA levels and increased hepatic content of APOA1 protein, the latter increase was observed in endothelial cells. A significant, inverse relationship was observed between plasma and hepatic APOA1 concentrations while a positive one was found between plasma levels of cysteine and APOA1. ConclusionThese data suggest an altered hepatic management of APOA1 and that cysteine may be involved in the control of this apolipoprotein at this level. Overall these findings represent a new aspect of dietary regulation of HDL at the hepatic transendothelial transport.

Calpain activation is required for homocysteine-mediated hepatic degradation of inhibitor Ikappa B alpha

Hepatic steatosis is a clinical feature observed in severe hyperhomocysteinemic patients. In mice, cystathionine beta synthase (CBS) deficiency, the most common cause of severe hyperhomocysteinemia, is also associated with steatosis, fibrosis and inflammation. Proinflammatory cytokines usually induce apoptosis. However, hyperhomocysteinemia does not increase apoptosis in liver of CBS-deficient mice compared to wild type mice. The aim of the study was to analyze the activation state of the NF-κB pathway in liver of CBS-deficient mice and to investigate its possible involvement in anti-apoptotic signals. We analyzed the level of IκBα in liver of CBS-deficient mice. A co-culture of primary hepatocytes and Kupffer cells was also used in order to investigate how IκBα degradation occurs in response to homocysteine. We found lower IκBα level not only in liver of CBS-deficient mice but also in hepatocyte/Kupffer cell co-culture. The homocysteine-mediated IκBα enhanced proteolysis occurred via calcium-dependent calpains, which was supported by an increased level of calpain activity and a reduced expression of calpastatin in liver of CBS-deficient mice. Intraperitoneal administration of the inhibitor PDTC normalized the expression of two genes induced by NF-κB activation, heme oxygenase-1 and cellular inhibitor of apoptosis 2. Moreover, PDTC administration induced an increase of caspase-3 activity in liver of CBS-deficient mice. Our results suggest that hyperhomocysteinemia induces calpain-mediated IκBα degradation which is responsible for anti-apoptotic signals in liver.

Genetic or nutritional disorders in homocysteine or folate metabolism increase proteinN‐homocysteinylation in mice

Genetic disorders of homocysteine (Hcy) or folate metabolism or high-methionine diets elevate plasma Hcy and its atherogenic metabolite Hcy-thiolactone. In humans, severe hyperhomocysteinemia due to genetic alterations in cystathionine beta-synthase (Cbs) or methylenetetrahydrofolate reductase (Mthfr) results in neurological abnormalities and premature death from vascular complications. In mouse models, dietary or genetic hyperhomocysteinemia results in liver or brain pathological changes and accelerates atherosclerosis. Hcy-thiolactone has the ability to form isopeptide bonds with protein lysine residues, which generates modified proteins (N-Hcy-protein) with autoimmunogenic and prothrombotic properties. Our aim was to determine how N-Hcy-protein levels are affected by genetic or nutritional disorders in Hcy or folate metabolism in mice. We found that plasma N-Hcy-protein was elevated 10-fold in mice fed a high-methionine diet compared with the animals fed a normal commercial diet. We also found that inactivation of Cbs, Mthfr, or the proton-coupled folate transporter (Pcft) gene resulted in a 10- to 30-fold increase in plasma or serum N-Hcy-protein levels. Liver N-Hcy-protein was elevated 3.4-fold in severely and 11-fold in extremely hyperhomocysteinemic Cbs-deficient mice, 3.6-fold in severely hyperhomocysteinemic Pcft mice, but was not elevated in mildly hyperhomocysteinemic Mthfr-deficient animals, suggesting that mice have a capacity to prevent accumulation of N-Hcy-protein in their organs. These findings provide evidence that N-Hcy-protein is an important metabolite associated with Hcy pathophysiology in the mouse.

Effect of hyperhomocysteinemia on the protein kinase DYRK1A in liver of mice

Hyperhomocysteinemia due to cystathionine beta synthase (CBS)-deficiency confers diverse clinical manifestations, notably liver diseases. Even if hyperhomocysteinemia in liver of CBS-deficient mice, a murine model of hyperhomocysteinemia, promotes mitochondrial oxidative stress and pro-apoptotic signals, protective signals may counteract these pro-apoptotic signals, leading to chronic inflammation. As DYRK1A, a serine/threonine kinase, has been described as a candidate antiapoptotic factor, we have analyzed the expression of DYRK1A in liver of CBS-deficient mice. We found that DYRK1A protein level was reduced in liver of CBS-deficient mice, which was not observed at the gene expression level. Moreover, the use of primary hepatocytes/Kupffer cells co-culture showed that degradation of DYRK1A induced by hyperhomocysteinemia requires calpain activation. Our results demonstrate a deleterious effect of hyperhomocysteinemia on DYRK1A protein expression, and emphasize the role of hyperhomocysteinemia on calpain activation.

Endothelial Dysfunction and Paradoxical Resistance to Thrombosis in a Transgenic Mouse Model of Severe Hyperhomocysteinemia.

Hyperhomocysteinemia induced by low folate or high methionine diets produces endothelial dysfunction and accelerated thrombosis in mice, but it is not known if these vascular effects are influenced by homocysteine-independent effects of dietary perturbation. To determine the vascular phenotype of severe hyperhomocysteinemia in the absence of dietary intervention, we utilized a recently developed transgenic mouse model of cystathionine β-synthase (CBS) deficiency. In this model, the early lethality of homozygous Cbs-deficient mice (Cbs-/-) is rescued by a zinc-inducible human CBSI278T (hCBS-I278T) transgene under the control of a metallotheinein promoter. The I278T mutation is a common CBS mutation found in human patients with homocystinuria. We bred Cbs+/− male to Cbs+/− hCBS-I278T female mice. The mothers were given drinking water supplemented with 25 mmol/L zinc sulfate. Pups were weaned at 4–5 weeks of age and did not receive supplemental zinc after weaning. At 20 weeks of age, plasma total homocysteine was significantly higher in Cbs-/- hCBS-I278T mice (350±17 μmol/L) compared with Cbs+/+ hCBS-I278T (8.0±0.6 μmol/L) or wild-type Cbs+/+ (7.2±0.8 μmol/L) littermates (P<0.001). Maximal dilatation of pial arterioles to the endotheliumdependent dilator, acetylcholine, was decreased significantly in Cbs-/- CBS-I278T mice (10±2 %) compared with Cbs+/+ hCBS-I278T (25±2 %) mice (P<0.001). Dilatation responses to the endothelium-independent vasodilator, nitroprusside, were similar in both groups. Surprisingly, the time to stable occlusion after photochemical injury (rose bengal and green laser) of the carotid artery was significantly delayed in Cbs-/- hCBSI278T mice (71±10 minutes) compared with Cbs+/+ hCBS-I278T (30±10 minutes) or Cbs+/+ mice (33±8 minutes) (P<0.05). The tail bleeding time was comparable in all 3 groups. We conclude that severe hyperhomocysteinemia due to genetic deficiency of Cbs produces endothelial dysfunction but not accelerated thrombosis in the absence of dietary intervention in mice.

Resveratrol supplementation worsen the dysregulation of genes involved in hepatic lipid homeostasis observed in hyperhomocysteinemic mice

Hyperhomocysteinemia is characterized by an increase of plasma homocysteine, a thiol-containing amino acid produced during methionine metabolism. Hyperhomocysteinemia has often been associated with coronary artery disease, vascular thrombosis and the development of premature atherosclerosis. We have recently demonstrated that the supplementation of catechin, a polyphenol found in the red wine, significantly reduced plasma homocysteine level in cystathionine beta synthase (CBS) deficient mice, a murine model of hyperhomocysteinemia. In the present study, we have investigated the influence of another well-studied polyphenol found in red wine, resveratrol, on hyperhomocysteinemia. After two months on high methionine diet, heterozygous Cbs deficient mice were administrated the resveratrol in drinking water (0.001%) for one month. High methionine diet significantly increased serum homocysteine levels, and decreased the serum activity of HDL-associated enzyme paraoxonase-1. Chronic administration of resveratrol significantly increased plasma homocysteine level, which was associated with a decreased serum paraoxonase-1 activity, in hyperhomocysteinemic mice. Then we looked at gene expression of several proteins involved in HDL stability and found a down-regulation of lecithin:cholesterol acyltransferase. In conclusion, we found a deleterious effect of resveratrol onto homocysteine and HDL metabolism in a murine model of hyperhomocysteinemia.

Effects of red wine polyphenolic compounds on paraoxonase-1 and lectin-like oxidized low-density lipoprotein receptor-1 in hyperhomocysteinemic mice

Hyperhomocysteinemia, or abnormally high plasma homocysteine (Hcy) concentration, has often been associated with vascular thrombosis and the development of premature atherosclerosis. Many studies have shown that moderate wine consumption has potential beneficial effects related to the prevention of atherosclerosis, in part attributed to the biological properties of polyphenolic components, mainly flavonoids. The aim of the present study is to determine the effects of a red wine polyphenolic extract (PE) administration on hyperhomocysteinemia due to cystathionine β-synthase (CBS) deficiency and on the associated biochemical markers of hepatic and endothelial dysfunctions in mice. Red wine PE was added for 4 weeks to the drinking water of heterozygous CBS-deficient mice fed a high-methionine diet, a murine model of hyperhomocysteinemia. Red wine PE supplementation at low dose significantly reduced plasma Hcy levels and restored the hepatic and plasma-decreased paraoxonase-1 activity induced by chronic hyperhomocysteinemia. Moreover, aortic expression of proinflammatory cytokines and adhesion molecules and levels of soluble lectin-like oxidized low-density lipoprotein receptor-1 were reduced in hyperhomocysteinemic mice fed the red wine PE supplementation. These findings suggest that red wine PE administration in low quantities has beneficial effects on biochemical markers of endothelial dysfunction due to hyperhomocysteinemia.

Mice lacking cystathionine beta synthase have lung fibrosis and air space enlargement

Cystathionine beta synthase (CBS) is a crucial regulator of plasma concentrations of homocysteine. Severe hyperhomocysteinemia due to CBS deficiency confers diverse clinical manifestations, notably pulmonary thrombotic disease. However, the association between hyperhomocysteinemia and chronic obstructive pulmonary disease is not well understood. To investigate the role of hyperhomocysteinemia in lung injury and pulmonary fibrosis, we analyzed the lung of CBS-deficient mice, a murine model of severe hyperhomocysteinemia. The degree of lung injury was assessed by histologic examination. Analysis of profibrogenic factors was performed by real-time quantitative reverse transcription-polymerase chain reaction. CBS-deficient mice develop fibrosis and air space enlargement in the lung, concomitant with an enhanced expression of heme oxygenase-1, pro(alpha)1 collagen type I, transforming growth factor-β1 and α-smooth muscle actin. However, lung fibrosis was found in the absence of increased inflammatory cell infiltrates as determined by histology, without changes in gene expression of proinflammatory cytokines TNFα and interleukin 6. The increased expression of α-smooth muscle actin and transforming growth factor-β1 emphasizes the role of myofibroblasts differentiation in case of lung fibrosis due to CBS deficiency in mice.

Hyperhomocysteinemia due to cystathionine beta synthase deficiency induces dysregulation of genes involved in hepatic lipid homeostasis in mice

Cystathionine beta synthase (CBS) deficiency leads to severe hyperhomocysteinemia, which confers diverse clinical manifestations, notably fatty liver. Recently, abnormal lipid metabolism has been demonstrated in CBS-deficient mice, a murine model of severe hyperhomocysteinemia. To gain further insights into effects of CBS deficiency on hepatic cholesterol metabolism, the expression of hepatic genes involved in biosynthesis, uptake and efflux was determined in CBS-deficient mice. Gene expression analysis was performed on liver of CBS-deficient mice using quantitative real-time PCR. We found that CBS-deficiency in liver mice significantly increases expression of genes induced by endoplasmic reticulum stress and genes that regulate the expression of enzymes required for cholesterol and fatty acid biosynthesis and uptake, notably the scavenger receptor class B type I (SR-BI), concomitant with overexpression of SR-BI at the protein level. Moreover, we also found increased mRNA levels of ABCG5, ABCG8, ABCG1 and ABCA1, which play important roles in reverse cholesterol transport, associated with an upregulation of liver X receptors and a downregulation of the peroxisome proliferators-activated receptor alpha. We found that several ATP-binding cassette transporters and nuclear hormone receptors involved in liver lipid homeostasis are differentially expressed in liver of CBS-deficient mice.