Lower mevalonate pyrophosphate decarboxylase activity is caused by the reduced amount of enzyme in stroke-prone spontaneously hypertensive rat

Stroke-prone spontaneously hypertensive rats have reduced hydroxysteroid 17-β dehydrogenase 7 levels for low cholesterol biosynthesis

Reduced serum cholesterol content was recently reported to be one of the factors responsible for cerebral haemorrhage. Stroke-prone spontaneously hypertensive rats (SHRSP) are known to have lower serum cholesterol content than normotensive Wistar-Kyoto rats (WKY). We previously reported that lower levels of mevalonate pyrophosphate decarboxylase (MPD) and squalene epoxidase (SQE), which are associated with cholesterol biosynthesis in the liver, are involved in the low serum cholesterol content in SHRSP. Here, we investigate the levels of sterol 14-demethylase (CYP51), methylsterol monooxygenase (SC4MOL), and hydroxysteroid 17-β dehydrogenase 7 (HSD17B7), which contribute to the cholesterol synthesis pathway in the conversion of lanosterol to zymosterol, in SHRSP and WKY. The HSD17B7 mRNA levels in the liver of SHRSP were markedly lower than those in WKY, whereas no significant differences were observed in CYP51 and SC4MOL levels in the two types of rats. The relative levels of protein, heteronuclear RNA, and mRNA of HSD17B7 were also significantly lower in SHRSP than in WKY. The degradation rates of HSD17B7 were the same in SHRSP and WKY. The protein levels of HSD17B7 were not significantly reduced in tissues other than the liver, including the brain, lung, heart, spleen, kidney, and testis, in SHRSP. Moreover, HSD17B7 activity was significantly lower in SHRSP than in WKY. Thus, our results indicated that low protein levels and activity of HSD17B7 are responsible for the reduced cholesterol content in SHRSP, indicating that HSD17B7, along with MPD and SQE, is involved in the decreased cholesterol synthesis in the liver of SHRSP.

Mevalonate Diphosphate Decarboxylase MVD/Erg19 Is Required for Ergosterol Biosynthesis, Growth, Sporulation and Stress Tolerance in Aspergillus oryzae

Mevalonate diphosphate decarboxylase (MVD; EC 4.1.1.33) is a key enzyme of the mevalonic acid (MVA) pathway. In fungi, the MVA pathway functions as upstream of ergosterol biosynthesis, and MVD is also known as Erg19. Previously, we have identified Aoerg19 in Aspergillus oryzae using bioinformatic analysis. In this study, we showed that AoErg19 function is conserved using phylogenetic analysis and yeast complementation assay. Quantitative reverse transcription-PCR (qRT-PCR) indicated that Aoerg19 expression changed in different growth stages and under different forms of abiotic stress. Subcellular localization analysis showed that AoErg19 was located in the vacuole. Overexpression of Aoerg19 decreased the ergosterol content in A. oryzae, which may due to the feedback-mediated downregulation of Aoerg8. Consistent with the decrease in ergosterol content, both Aoerg19 overexpression and RNAi strains of A. oryzae are sensitive to abiotic stressors, including ergosterol biosynthesis inhibitor, temperature, salt and ethanol. Thus, we have identified the function of AoErg19 in A. oryzae, which may assist in genetic modification of MVA and the ergosterol biosynthesis pathway.

Functional and conformational transitions of mevalonate diphosphate decarboxylase from Bacopa monniera

Functional and conformational transitions of mevalonate diphosphate decarboxylase (MDD), a key enzyme of mevalonate pathway in isoprenoid biosynthesis, from Bacopa monniera (BmMDD), cloned and overexpressed in Escherichia coli were studied under thermal, chemical and pH-mediated denaturation conditions using fluorescence and Circular dichroism spectroscopy. Native BmMDD is a helix dominant structure with 45% helix and 11% sheets and possesses seven tryptophan residues with two residues exposed on surface, three residues partially exposed and two situated in the interior of the protein. Thermal denaturation of BmMDD causes rapid structural transitions at and above 40°C and transient exposure of hydrophobic residues at 50°C, leading to aggregation of the protein. An acid induced molten globule like structure was observed at pH 4, exhibiting altered but compact secondary structure, distorted tertiary structure and exposed hydrophobic residues. The molten globule displayed different response at higher temperature and similar response to chemical denaturation as compared to the native protein. The surface tryptophans have predominantly positively charged amino acids around them, as indicated by higher KSV for KI as compared to that for CsCl. The native enzyme displayed two different lifetimes, τ1 (1.203±0.036 ns) and τ2 (3.473±0.12 ns) indicating two populations of tryptophan.

Involvement of microRNA214 and transcriptional regulation in reductions in mevalonate pyrophosphate decarboxylase mRNA levels in stroke-prone spontaneously hypertensive rat livers

Hypocholesterolemia has been epidemiologically identified as one of the causes of stroke (cerebral hemorrhage). We previously reported that lower protein levels of mevalonate pyrophosphate decarboxylase (MPD), which is responsible for reducing serum cholesterol levels in stroke-prone spontaneously hypertensive rats (SHRSP), in the liver were caused by a reduction in mRNA levels. However, the mechanism responsible for reducing MPD expression levels in the SHRSP liver remains unclear. Thus, we compared microRNA (miR)-214 combined with the 3'-untranslated region of MPD mRNA and heterogeneous nuclear RNA (hnRNA) between SHRSP and normotensive Wistar Kyoto rats (WKY). miR-214 levels in the liver were markedly higher in SHRSP than in WKY, whereas hnRNA levels were significantly lower. These results indicate that the upregulation of miR-214 and downregulation of MPD transcription in the liver both play a role in the development of hypocholesterolemia in SHRSP.

Tissue-specific effects of atorvastatin on 3-hydroxy-3-methylglutarylcoenzyme A reductase expression and activity in spontaneously hypertensive rats

AIM

Cardiovascular remodeling is closely associated with cholesterol and is attenuated by statins. The spontaneously hypertensive rat (SHR) has a low serum cholesterol level and evident cardiovascular remodeling. The aims of the present study were to characterize the effects of atorvastatin on tissue cholesterol content and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase expression and activity in four tissues from SHR: liver, heart, aorta and kidney.

METHODS

SHR and normotensive Wistar-Kyoto rats (WKY) were treated daily with atorvastatin (50 mg/kg) for 8 weeks. Cholesterol levels of serum and tissues (liver, heart, aorta and kidney) were determined by commercial enzymatic methods. Western blot analysis and high performance liquid chromatogram (HPLC) were used to assay the expression and activity of enzyme respectively.

RESULTS

Treatment with atorvastatin decreased cholesterol content and HMGCoA reductase expression and activity in all four tissues of SHR. However, in WKY, atorvastatin only altered HMG-CoA reductase in liver, where the protein expression was upregulated but the enzyme activity was decreased.

CONCLUSION

The present study demonstrates that the effects of atorvastatin on tissue cholesterol content and HMG-CoA reductase are strain- and tissue-specific.

Comparison of Biochemical Properties and Protein Level of Mevalonate Pyrophosphate Decarboxylase between Stroke-prone Spontaneously Hypertensive Rats and Wistar-Kyoto Rats

The spontaneously hypertensive rat (stroke-prone) (SHRSP) experiences severe hypertension and cerebral hemorrhage. The serum cholesterol level in this rat is lower than that in the normotensive Wistar-Kyoto rat. Epidemiologic studies have indicated a negative association between serum cholesterol level and the incidence of cerebral hemorrhage in humans. Therefore the low level of serum cholesterol in SHRSP may cause cerebral strokes. The following investigation demonstrated that the activity for the biosynthesis of cholesterol is decreased in SHRSP due to the reduced activity of mevalonate pyrophosphate decarboxylase (MPD). However, the mechanism underlying the reduced activity of this enzyme remains unclear. In this review, we indicate that the level of MPD in the brain and liver of SHRSP is reduced from the age of 2 weeks.

Change in the protein level of mevalonate pyrophosphate decarboxylase in tissues of mouse by pravastatin

We previously reported that treatment of rats with a diet containing 0.1% pravastatin and 5% cholestyramine markedly increased mevalonate pyrophosphate decarboxylase (MPD) activity in liver crude extracts compared with nontreated rats. In this study, we examined the change in the protein level of MPD in the tissues of mice administered pravastatin. When MPD content in the tissues of nontreated mice was analyzed by quantitative immunoblotting, a single protein band with an apparent molecular weight of 46 kDa was detected in all tissues and the specific protein content of MPD in liver and kidney was markedly higher than that in other tissues. When MPD content in the tissues of pravastatin-treated mice was analyzed by immunoblotting, MPD was markedly increased (9-fold) only in the liver compared with nontreated mice. Next, when MPD activity was measured in the liver between nontreated and pravastatin-treated mice, MPD activity as well as protein levels were markedly increased (11-fold) in the liver of pravastatin-treated mice compared with nontreated mice. These data suggest that a marked induction of MPD in the liver by pravastatin is responsible for the tissue-specific effect of pravastatin.

Mortalin-MPD (mevalonate pyrophosphate decarboxylase) interactions and their role in control of cellular proliferation

Mortalin (mot-2/GRP75/PBP74/mthsp70) is a member of the hsp70 family of proteins and is differentially distributed in normal and immortal cells. It was shown to be involved in pathways to cell senescence and immortalization. To elucidate its functional aspects, a yeast interactive screen for mortalin (mot-2) binding proteins was performed. Mevalonate pyrophosphate decarboxylase (MPD) was identified as one of the mortalin binding partners. The interactions were confirmed in mammalian cells by two-hybrid assay and in vivo coimmunoprecipitation. MPD is known to furnish prenyl groups required for prenylation, protein modification that is essential for the activity of many proteins including p21(Ras) (Ras). We have examined the effect of MPD-mot-2 interactions on the level and activity of p21(Ras) and its downstream effectors, p44 and p42 MAP kinases (ERK1/ERK2), in Ras-Raf pathway. An overexpression of mot-2 resulted in reduced level of Ras and phosphorylated ERK2. These were rescued by co-expression of MPD from an exogenous promoter demonstrating a functional link between mot-2, MPD, and Ras. Ras and its oncogenic forms act as key players in controlling proliferation of normal and cancerous cells. Assigning mot-2 upstream of p21(Ras) offers an important mechanism for influence over cell proliferation.

Mevalonate pyrophosphate decarboxylase in stroke-prone spontaneously hypertensive rat is reduced from the age of two weeks

We carried out a comparison of tissue distribution of mevalonate pyrophosphate decarboxylase (MPD) between normotensive Wistar Kyoto rat (WKY) and stroke-prone spontaneously hypertensive rat (SHRSP) using Western blotting. However, there was no difference in tissue distribution of MPD between WKY and SHRSP, expect in brain and liver. We then compared the MPD between WKY and SHRSP liver at several weeks of age. We found that MPD in the liver as well as brain of SHRSP was significantly reduced from two weeks of age. This data is useful to identify or understand the mechanism underlying the reduced amount of MPD in SHRSP.