Introduction: Statins are one of the approved drugs used in the clinic, which are prescribed to reduce the amount of cholesterol in the blood of patients. However, the effects of the drug in reducing the amount of fat and the occurrence of side effects are not the same in the patients. Considering the role of LncRNAs in regulating gene expression, the possible role of HOTAIR LncRNA and atorvastatin treatment in regulating HMGCR gene expression as the main regulating gene in cholesterol synthesis has been investigated. Methods: Bioinformatics analyses were used to find common regulatory factors between the HMGCR gene and candidate LncRNAs. MTT assay was used to determine the optimal dose of atorvastatin treatment on the HepG2 cell line. RNA extraction, cDNA synthesis, and quantitative analysis of gene expression were performed by qPCR. Finally, HMGCR protein expression was evaluated via the Western blot technique. Results: Bioinformatic analyses showed that there is a relationship between HMGCR expression and some LncRNAs (HOTAIR, TUG1, MALAT1, GAS5, JPX, DLX6AS). In the cell culture, atorvastatin treatment increased the expression of HMGCR at mRNA and protein levels in the HepG2 cell line. Among the candidate lncRNAs, HOTAIR LncRNA expression decreased by 80% under atorvastatin treatment. Downregulating of the HOTAIR gene led to increased HMGCR gene expression at the RNA and protein levels. Conclusion: The results of this study indicated that, aside from blocking the HMGCR enzyme binding site, atorvastatin can regulate the expression of HMGCR mRNA and protein by changing the HOTAIR expression.

Background: Rebaudioside A is one of the major diterpene glycosides found in Stevia had been reported to possess anti-hyperlipidemic effects. In this study, we explore the potential cholesterol-regulating mechanisms of Rebaudioside A in the human hepatoma (HepG2) cell line in comparison with simvastatin. Methods: Cells were incubated with Rebaudioside A at several concentrations (0-10 μ, M) to determine the cytotoxicity by the MTT assay. Cells were treated with selected dosage (1 and 5 μ, M) in further experiments. Total cellular lipid was extracted by Bligh and Dyer method and subjected to quantitative colorimetric assay. To illustrate the effect of Rebaudioside A on cellular lipid droplets and low-density lipoprotein receptors, treated cells were subjected to immunofluorescence microscopy. Finally, we investigated the expression of experimental gene patterns of cells in response to treatment. Results: In this study, cytotoxicity of Rebaudioside A was determined at 27. 72 μ, M. Treatment of cells with a higher concentration of Rebaudioside A promotes better hepatocellular cholesterol internalization and ameliorates cholesterol-regulating genes such as HMGCR, LDLR, and ACAT2. Conclusions: In conclusion, our data demonstrated that Rebaudioside A is capable to regulate cholesterol levels in HepG2 cells. Hence, we proposed that Rebaudioside A offers a potential alternative to statins for atherosclerosis therapy.

Dysregulation of brain cholesterol homeostasis causes the accumulation of extracellular protein deposits called amyloid plaques in the hippocampus which eventually leads to neuronal death, memory and learning deficits. The aim of the present study was to investigate the effect of beta amyloid on miRNAs regulating HMGCR and ABCA1 as cholesterol synthesis and homeostasis genes. Primary astrocytes were isolated from C57BL/6J mice, and were treated with 0. 5 μM amyloid beta (Aβ). Expression levels of genes and miRNAs were measured by real-time PCR. In comparison to control, Aβ treatment resulted in a significant decrease in miR-96-5p expression as a positive and negative regulator of HMGCR and ABCA1, respectively. There was no significant increase in miR-27a-3p expression as a negative regulator of HMGCR. miR-106b-5p and miR-143-3p expressions were also dramatically decreased as ABCA1 negative regulators. Amyloid beta can alter the expression of major genes in the cholesterol homeostasis pathway via their regulatory miRNAs.

Background: Elevated brain cholesterol increases the risk of Alzheimer's disease. Production of 24-hydroxycholesterol (24s-OHC) by neurons prevents cholesterol accumulation in the brain. In this study, we investigated the effect of 24s-OHC on the HMG-COA reductase and ABCA1 which are involved in the brain cholesterol homeostasis with or without β-amyloid in astrocytes. Methods and Materials: Astrocytes were treated with 24s-OHC with or without Aβ. Western blot and real-time polymerase chain reaction were done to detect protein and gene expression of β-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) and ABCA1, respectively. Cholesterol release was determined using a quantitation kit. Results: Protein levels of HMGCR and ABCA1 were significantly increased by Aβ,however, the 24s-OHC was able to restore their levels and diminish the effect of amyloid-β. Aβ did not have a significant effect on HMGCR expression, while 24s-OHC reduced it by 68%. Aβ-induced ABCA1 expression did not increase cholesterol efflux as the lower levels of cholesterol in conditioned medium of Aβ-treated cells were found. Conclusion: Our novel findings show that Aβ affects two key elements in the brain cholesterol homeostasis, HMGCR and ABCA1, which are crucial in cholesterol synthesis and efflux. Since 24s-OHC could suppress the Aβ effects on enhancement of HMGCR and ABCA1, therefore the cytochrome P450 46A1 (Cyp46A1), which is exclusively expressed in the central nervous system and responsible for producing of 24s-OHC, could consider as a therapeutic target in the cholesterol-related neurodegenerative diseases such as Alzheimer's disease.

Background: This in silico study investigated the association between the local biosynthesis of cholesterol and mammographic density, the major risk of developing breast cancer, as a function of the three cellular components of breast tissue (epithelium, fatty, and non-fatty stroma). Methods: The study compared the expression of 7 genes (HMGCR, FDPS, FDFT1, GGPS1, SQLE, LSS, and SREBF2) involved in the de novo cholesterol biosynthesis, first, according to the radiological density (dense vs. non-dense breast) and, then, according to the cellular components of breast tissue, regardless the radiological classification. Results: HMGCR, SQLE, and SBREF2 were significantly more expressed in radiologically dense than in non-dense breasts (-1.70 vs. -1.41, P=0.0028; -1.20 vs. -1.11, P=0.0501; -3.63 vs. -3.31 P=0.0003; -0.92 vs. -0.76, P=0.0271, respectively). When the samples were reclassified based on their cellular components as highly fatty and highly non-fatty, HMGCR, SQLE, and SBREF2 were significantly more expressed in highly non-fatty samples (-1.48 vs. -1.94, P<0.0001; -3.39 vs. -4.18, P<0.0001; -0.77 vs. -0.94, P=0.0103, respectively) whereas LSS was overexpressed in high fatty ones (0.28 vs. -0.60, P<0.0001). Besides, while in the highly non-fatty subgroup SREBF2 was positively associated with both HMGCR (r=0.53, P<0.0001) and SQLE (r=0.73, P<0.0001), in the highly fatty subgroup these positive correlations disappeared (SREBF2*HMGCR: r=-0.19, P=0.3026) or substantially decreased (SREBF2*SQLE: r=0.41, P=0.0173). Conclusion: Findings provide a compelling biological explanation for the clinical evidence that women with radiologically dense breasts are at a higher risk of developing cancer compared to those with non-dense breasts because of the prevalence of non-fatty tissue, where the altered expression of genes leading to an increased cholesterol production, can contribute to the transformation of epithelial cells, and support the use of mammographic density as a reliable surrogate marker to identify women who may benefit from a preventive treatment aimed at reducing cholesterol production.

Objective: Dysregulation of cholesterol metabolism in the brain is responsible for many lipid storage disorders, including Niemann-Pick disease type C (NPC). Here, we have investigated whether cyclodextrin (CD) and apolipoprotein A-I (apoA-I) induce the same signal to inhibit cell cholesterol accumulation by focusing on the main proteins involved in cholesterol homeostasis in response to CD and apoA-I treatment. Materials and Methods: In this experimental study, astrocytes were treated with apoA-I or CD and then lysed in RIPA buffer. We used Western blot to detect protein levels of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGCR) and ATP-binding cassette transporter A1 (ABCA1). Cell cholesterol content and cholesterol release in the medium were also measured. Results: ApoA-I induced a significant increase in ABCA1 and a mild increase in HMGCR protein level, whereas CD caused a significant increase in HMGCR with a significant decrease in ABCA1. Both apoA-I and CD increased cholesterol release in the medium. A mild, but not significant increase, in cell cholesterol content was seen by apoA-I; however, a significant increase in cell cholesterol was detected when the astrocytes were treated with CD. Conclusion: CD, like apoA-I, depletes cellular cholesterol. This depletion occurs in a different way from apoA-I that is through cholesterol efflux. Depletion of cell cholesterol with CDs led to reduced protein levels of ABCA1 along with increased HMGCR and accumulation of cell cholesterol. This suggested that CDs, unlike apoA-I, could impair the balance between cholesterol synthesis and release, and interfere with cellular function that depends on ABCA1.

Alteration in cholesterol homeostasis is a consequence of overweight and obesity induced by diet, with the liver being one of the key organs in the cholesterol synthesis pathway. Since the effect of rice bran and aerobic exercise on the hepatic cholesterol synthesis pathway is not well understood, this study aimed to investigate the effect of aerobic exercise and ethanolic extract of rice bran on the expression of Acetyl-CoA carboxylase and HMGCR genes in the liver tissue of rats fed with a high-fat diet. In a preclinical trial, 30 eight-week-old female rats were randomly divided into five groups (6 rats per group): control with normal diet, control with a high-fat diet, aerobic exercise with a high-fat diet, and aerobic exercise with rice bran and a high-fat diet. The aerobic exercise program included running on a treadmill at moderate intensity (50-60% Vo2max), 5 sessions per week for 4 weeks. The ethanolic extract of rice bran was administered at a dose of 60 mg/kg via gavage to the supplement and exercise-supplement groups. The expression of Acetyl-CoA carboxylase in the control group with a normal diet significantly increased compared to the control group with a high-fat diet (P = 0. 000), while the expression of HMGCR significantly decreased (P = 0. 050). Additionally, the expression of Acetyl-CoA carboxylase in the aerobic exercise group with a high-fat diet showed a significant increase compared to the control group with a high-fat diet (P ≤ 0. 034), and the expression of HMGCR showed a significant decrease (P = 0. 000). Furthermore, intergroup comparisons revealed that the increase in the expression of Acetyl-CoA carboxylase in the rice bran diet group was significant compared to the control group with a high-fat diet (P ≤ 0. 001), while the expression of HMGCR significantly decreased (P ≤ 0. 028). Similar changes were observed in the aerobic exercise-rice bran group compared to the control group with a high-fat diet, showing a significant increase in the expression of Acetyl-CoA carboxylase (P ≤ 0. 002), while the decrease in HMGCR expression was significant (P = 0. 000).

Objective: Regulation of cholesterol level is essential for the brain optimal function. The beneficial effect of garlic consumption on cholesterol homeostasis is well known; however, the molecular mechanism to support its properties is unclear. Here, we investigated the beneficial effect of aqueous extract of garlic and allicin on lipid profile and the main players involved in brain cholesterol homeostasis including ABCA1, HMG-CoA reductase, and CYP46A1 in both C57BL/6J mice brain and astrocytes. Materials and Methods: Thirty mice were divided into control and garlic groups. Garlic group was fed with the aqueous extract of garlic. Serum lipids were measured and brain protein levels of ABCA1, HMGCR, and CYP46A1 were determined by western blotting. Changes in these proteins expression were also studied in the presence of allicin in cultured astrocytes. Results: A moderate decrease in serum total cholesterol and a significant increase in plasma HDL-C levels (p<0. 05) were detected. A significant increase in ABCA1, HMGCR, and CYP46A1 protein levels was observed in the garlic group and in the cultured astrocytes treated with allicin by western blotting (p<0. 05). Conclusion: Our findings indicated that the main players involved in cholesterol turnover including HMGCR that is involved in cholesterol synthesis, ABCA1 that is important in cholesterol efflux, and CYP46A1 that is necessary in cholesterol degradation, were up regulated by garlic/allicin in both animal and cell culture model. We concluded that increasing cholesterol turnover is a possible mechanism for the beneficial effects of garlic in cholesterol homeostasis.