Age-dependent increase in desmosterol restores DRM formation and membrane-related functions in cholesterol-free DHCR24-/- mice

Virtual Screening of Novel 24-Dehydroxysterol Reductase (DHCR24) Inhibitors and the Biological Evaluation of Irbesartan in Cholesterol-Lowering Effect

Hyperlipidemia is a risk factor for the development of fatty liver and cardiovascular diseases such as atherosclerosis and coronary heart disease, and hence, cholesterol-lowering drugs are considered important and effective in preventing cardiovascular diseases. Thus, researchers in the field of new drug development are endeavoring to identify new types of cholesterol-lowering drugs. 3β-hydroxysterol-Δ(24)-reductase (DHCR24) catalyzes the conversion of desmosterol to cholesterol, which is the last step in the cholesterol biosynthesis pathway. We speculated that blocking the catalytic activity of DHCR24 could be a novel therapeutic strategy for treating hyperlipidemia. In the present study, by virtually screening the DrugBank database and performing molecular dynamics simulation analysis, we selected four potential DHCR24 inhibitor candidates: irbesartan, risperidone, tolvaptan, and conivaptan. All four candidates showed significant cholesterol-lowering activity in HepG2 cells. The experimental mouse model of hyperlipidemia demonstrated that all four candidates improved high blood lipid levels and fat vacuolation in the livers of mice fed with a high-fat diet. In addition, Western blot analysis results suggested that irbesartan reduced cholesterol levels by downregulating the expression of the low-density lipoprotein receptor. Finally, the immune complex activity assay confirmed the inhibitory effect of irbesartan on the enzymatic activity of DHCR24 with its half-maximal inhibitory concentration (IC50) value of 602 nM. Thus, to the best of our knowledge, this is the first study to report that blocking the enzymatic activity of DHCR24 via competitive inhibition is a potential strategy for developing new cholesterol-lowering drugs against hyperlipidemia or multiple cancers. Furthermore, considering that irbesartan is currently used to treat hypertension combined with type 2 diabetes, we believe that irbesartan should be a suitable choice for patients with both hypertension and hyperlipidemia.

The role of DHCR24 in the pathogenesis of AD: re-cognition of the relationship between cholesterol and AD pathogenesis

Previous studies show that 3β-hydroxysterol-Δ24 reductase (DHCR24) has a remarked decline in the brain of AD patients. In brain cholesterol synthetic metabolism, DHCR24 is known as the heavily key synthetase in cholesterol synthesis. Moreover, mutations of DHCR24 gene result in inhibition of the enzymatic activity of DHCR24, causing brain cholesterol deficiency and desmosterol accumulation. Furthermore, in vitro studies also demonstrated that DHCR24 knockdown lead to the inhibition of cholesterol synthesis, and the decrease of plasma membrane cholesterol and intracellular cholesterol level. Obviously, DHCR24 could play a crucial role in maintaining cholesterol homeostasis via the control of cholesterol synthesis. Over the past two decades, accumulating data suggests that DHCR24 activity is downregulated by major risk factors for AD, suggesting a potential link between DHCR24 downregulation and AD pathogenesis. Thus, the brain cholesterol loss seems to be induced by the major risk factors for AD, suggesting a possible causative link between brain cholesterol loss and AD. According to previous data and our study, we further found that the reduced cholesterol level in plasma membrane and intracellular compartments by the deficiency of DHCR24 activity obviously was involved in β-amyloid generation, tau hyperphosphorylation, apoptosis. Importantly, increasing evidences reveal that the brain cholesterol loss and lipid raft disorganization are obviously linked to neuropathological impairments which are associated with AD pathogenesis. Therefore, based on previous data and research on DHCR24, we suppose that the brain cholesterol deficiency/loss might be involved in the pathogenesis of AD.

Genome Wide Analysis for Growth at Two Growth Stages in A New Fast-Growing Common Carp Strain (Cyprinus carpio L.)

In order to identify candidate genes or loci associated with growth performance of the newly established common carp strain, Xinlong, we conducted a genome-wide association analysis using 2b-RAD technology on 123 individuals. We constructed two sets of libraries associated with growth-related parameters (weight, length, width and depth) measured at two different grow-out stages. Among the 413,059 SNPs identified using SOAP SNP calling, 147,131 were tested for GWAS after quality filtering. Finally, 39 overlapping SNPs, assigned to four genomic locations, were associated with growth traits in two stages. These loci were assigned to functional classes related to immune response, response to stress, neurogenesis, cholesterol metabolism and development, and proliferation and differentiation of cells. By overlapping results of Plink and EMMAX analyses, we identified three genes: TOX, PLK2 and CD163 (both methods P < 0.05). Our study results could be used for marker-assisted selection to further improve the growth of the Xinlong strain, and illustrate that largely different sets of genes drive the growth of carp in the early and late grow-out stages.

Male germ cell-specific knockout of cholesterogenic cytochrome P450 lanosterol 14α-demethylase (Cyp51)

Cytochrome P450 lanosterol 14α-demethylase (CYP51) and its products, meiosis-activating sterols (MASs), were hypothesized by previous in vitro studies to have an important role in regulating meiosis and reproduction. To test this in vivo, we generated a conditional male germ cell-specific knockout of the gene Cyp51 in the mouse. High excision efficiency of Cyp51 allele in germ cells resulted in 85-89% downregulation of Cyp51 mRNA and protein levels in germ cells. Quantitative metabolic profiling revealed significantly higher levels of CYP51 substrates lanosterol and 24,25-dihydrolanosterol and substantially diminished levels of MAS, the immediate products of CYP51. However, germ cell-specific ablation of Cyp51, leading to lack of MAS, did not affect testicular morphology, daily sperm production, or reproductive performance in males. It is plausible that due to the similar structures of cholesterol intermediates, previously proposed biological function of MAS in meiosis progression can be replaced by some other yet-unidentified functionally redundant lipid molecule(s). Our results using the germ cell-specific knockout model provide first in vivo evidence that the de novo synthesis of MAS and cholesterol in male germ cells is most likely not essential for spermatogenesis and reproduction and that MASs, originating from germ cells, do not cell-autonomously regulate spermatogenesis and fertility.

Effect of methylene blue on the genomic response to reperfusion injury induced by cardiac arrest and cardiopulmonary resuscitation in porcine brain

BACKGROUND

Cerebral ischemia/reperfusion injury is a common secondary effect of cardiac arrest which is largely responsible for postresuscitative mortality. Therefore development of therapies which restore and protect the brain function after cardiac arrest is essential. Methylene blue (MB) has been experimentally proven neuroprotective in a porcine model of global ischemia-reperfusion in experimental cardiac arrest. However, no comprehensive analyses have been conducted at gene expression level.

METHODS

Pigs underwent either untreated cardiac arrest (CA) or CA with subsequent cardiopulmonary resuscitation (CPR) accompanied with an infusion of saline or an infusion of saline with MB. Genome-wide transcriptional profiling using the Affymetrix porcine microarray was performed to 1) gain understanding of delayed neuronal death initiation in porcine brain during ischemia and after 30, 60 and 180 min following reperfusion, and 2) identify the mechanisms behind the neuroprotective effect of MB after ischemic injury (at 30, 60 and 180 min).

RESULTS

Our results show that restoration of spontaneous circulation (ROSC) induces major transcriptional changes related to stress response, inflammation, apoptosis and even cytoprotection. In contrast, the untreated ischemic and anoxic insult affected only few genes mainly involved in intra-/extracellular ionic balance. Furthermore, our data show that the neuroprotective role of MB is diverse and fulfilled by regulation of the expression of soluble guanylate cyclase and biological processes accountable for inhibition of apoptosis, modulation of stress response, neurogenesis and neuroprotection.

CONCLUSIONS

Our results support that MB could be a valuable intervention and should be investigated as a therapeutic agent against neural damage associated with I/R injury induced by cardiac arrest.

How essential is cholesterol?

Cholesterol is an apparently indispensable lipid for numerous processes required for cell proliferation. Levels of this molecule are primarily regulated at the transcriptional level by the SREBPs (sterol-regulatory-element-binding proteins) and LXR (liver X receptor). In this issue of the Biochemical Journal, Rodríguez-Acebes et al. show that a cholesterol precursor, desmosterol, can support cell proliferation in the absence of cholesterol in a murine macrophage-like model (J774-D cells). These cells are defective in DHCR24 (sterol-Delta24-reductase, or 3beta-hydroxysterol Delta24-reductase), leading to desmosterol accumulation, and yet sterol homoeostasis appears to be normal with respect to SREBP processing and LXR activation. Other potentially cholesterol-dependent processes which were not the focus of this study are briefly discussed, such as lipid-raft-dependent cell signalling.