👤 T J van Berkel

Polycystic ovary syndrome (PCOS) is a heterogeneous reproductive endocrine condition in women, with implications in fertility and long-term metabolic health. PCOS with hyperandrogen (HA-PCOS; hyperandrogenic PCOS) has been recently identified as one of the four subtypes of PCOS. Dyslipidemia is known to be associated with clinical hyperandrogenism in PCOS. Indeed, patients with HA-PCOS were found to have the highest incidence of dyslipidemia among patients with the other three subtypes of PCOS. In the present study, we identified genes involved in lipid-associated processes (namely, lipid biosynthetic process, lipid catabolic process, hyperlipidemia, hypolipidemia and lipid homeostasis) whose expression are changed in granulosa cells from HA-PCOS patients compared to those from non-PCOS women, in order to identify molecular factors contributing to the highest risk of dyslipidemia incidence observed in patients with hyperandrogenic PCOS. We found 27 lipid biology-associated genes (ACSM1, ACSM3, AGPAT4, AJUBA, ALDH1A2, CCDC3, LPL, P2RX1, PITPNM1, PRLR, PTGIS, SLC44A5, SPTSSB, ST8SIA5, IDH1, ITPKA, PPM1L, SPTLC2, ADRA2A, ASPG, IRS1, PLB1, IDH1, LCT, NUDT8, SMPDL3A and SYNE2) whose transcript levels are significantly downregulated or upregulated in granulosa cells of women with HA-PCOS compared to those in control women. The majority of these genes have not been previously studied in the context of PCOS, and are possible candidates for further research to better understand the contribution of high androgen levels to dyslipidemia in PCOS. Targeting of high androgen-induced dyslipidemia might be of high clinical importance in the treatment of women with HA-PCOS. Show less

The zinc finger protein Znf202 is a transcriptional suppressor of lipid related genes and has been linked to hypoalphalipoproteinemia. A functional role of Znf202 in lipid metabolism in vivo still remains to be established. We generated mouse Znf202 expression vectors, the functionality of which was established in several in vitro systems. Next, effects of adenoviral znf202 overexpression in vivo were determined in normo- as well as hyperlipidemic mouse models. Znf202 overexpression in mouse hepatoma cells mhAT3F2 resulted in downregulation of members of the Apoe/c1/c2 and Apoa1/c3/a4 gene cluster. The repressive activity of Znf202 was firmly confirmed in an apoE reporter assay and Znf202 responsive elements within the ApoE promoter were identified. Adenoviral Znf202 transfer to Ldlr-/- mice resulted in downregulation of apoe, apoc1, apoa1, and apoc3 within 24 h after gene transfer. Interestingly, key genes in bile flux (abcg5/8 and bsep) and in bile acid synthesis (cyp7a1) were also downregulated. At 5 days post-infection, the expression of the aforementioned genes was normalized, but mice had developed severe hepatosteatosis accompanied by hypercholesterolemia and hypoalphalipoproteinemia. A much milder phenotype was observed in wildtype mice after 5 days of hepatic Znf202 overexpression. Interestingly and similar to Ldl-/- mice, HDL-cholesterol levels in wildtype mice were lowered after hepatic Znf202 overexpression. Znf202 overexpression in vivo reveals an important role of this transcriptional regulator in liver lipid homeostasis, while firmly establishing the proposed key role in the control of HDL levels. Show less

Since high expression of farnesoid X receptor (FXR) has been detected in glucocorticoid-producing adrenocortical cells, we evaluated the potential role of FXR in adrenal glucocorticoid production. FXR agonist GW4064 increased fasting plasma corticosterone levels (+45%; P<0.01) in C57BL/6 mice, indicative of enhanced adrenal steroidogenesis. GW4064 treatment did not affect plasma ACTH levels, adrenal weight, or adrenal expression of steroidogenic genes. Scavenger receptor BI (SR-BI) mRNA and protein expression, respectively, increased 1.9-fold (P<0.01) and 1.5-fold, which suggests a stimulated lipoprotein-associated cholesterol uptake into the adrenals upon GW4064 treatment. In line with an enhanced flux of cellular cholesterol into the steroidogenic pathway, adrenal unesterified and esterified cholesterol stores were 21-41% decreased (P<0.01) upon GW4064 treatment. In conclusion, we have shown that the FXR agonist GW4064 stimulates plasma corticosterone levels in C57BL/6 mice. Our findings suggest a novel role for FXR in the modulation of adrenal cholesterol metabolism and glucocorticoid synthesis in mice. Show less

Macrophages serve essential functions as regulators of immunity and homeostasis, and their proliferation contributes to pathogenesis of certain disorders. In this report, we show that induction of macrophage proliferation by the growth factor M-CSF is negatively modulated by agonists that activate the nuclear receptor liver X receptor (LXR), both in vitro and in vivo. Both isoforms LXR α and β are involved in the antiproliferative actions of LXR ligands in macrophages. In contrast, M-CSF does not exert negative effects on LXR-mediated gene expression. Treatment with LXR agonists results in the accumulation of macrophages in the G(0)/G(1) phase of the cell cycle without affecting ERK-1/2 phosphorylation. The use of small interfering RNA or genetically modified mice revealed that, in contrast to other cellular models, functional expression of either the cyclin-dependent kinase inhibitor p27KIP1 or the cholesterol transporters ATP-binding cassette A1 or ATP-binding cassette G1 was not required for the antiproliferative effects of LXR agonists in macrophages. Western blot analysis revealed that protein expression of key molecules that regulate progression through the cell cycle, such as cyclins D1 and B1 and cyclin-dependent kinases 2 and 4, was downregulated upon LXR activation. These observations suggest a role for LXR agonists in limiting macrophage proliferative responses associated to pathogenic disorders. Show less

Receptor-mediated cholesterol uptake has been suggested to play a role in maintaining the adrenal intracellular free cholesterol pool and the ability to produce hormones. Therefore, in the current study, we evaluated the importance of scavenger receptor class B type I (SR-BI)-mediated cholesteryl ester uptake from HDL for adrenal glucocorticoid hormone synthesis in vivo. No difference was observed in the plasma level of corticosterone between SR-BI-deficient and wild-type mice under ad libitum feeding conditions. Overnight fasting ( approximately 16 h) stimulated the plasma level of corticosterone by 2-fold in wild-type mice. In contrast, no effect of fasting on plasma corticosterone levels was observed in SR-BI-deficient mice, leading to a 44% lower plasma corticosterone level compared with their wild-type littermate controls. In parallel, an almost complete depletion of lipid stores in the adrenal cortex of fasted SR-BI-deficient mice was observed. Plasma adrenocorticotropic hormone levels were increased by 5-fold in fasted SR-BI-deficient mice. SR-BI deficiency induced marked changes in the hepatic expression of the glucocorticoid-responsive genes cholesterol 7alpha-hydroxylase, HMG-CoA synthase, apolipoprotein A-IV, corticosteroid binding globulin, interleukin-6, and tumor necrosis factor-alpha, which coincided with a 42% decreased plasma glucose level under fasting conditions. In conclusion, we show that the absence of adrenal HDL cholesteryl ester uptake in SR-BI-deficient mice impairs the adrenal glucocorticoid-mediated stress response to fasting as a result of adrenal glucocorticoid insufficiency and attenuated liver glucocorticoid receptor signaling, leading to hypoglycemia under fasting conditions. Show less

Previous studies with hypertriglyceridemic APOC3 transgenic mice have suggested that apolipoprotein C-III (apoC-III) may inhibit either the apoE-mediated hepatic uptake of TG-rich lipoproteins and/or the lipoprotein lipase (LPL)-mediated hydrolysis of TG. Accordingly, apoC3 knockout (apoC3(-/-)) mice are hypotriglyceridemic. In the present study, we attempted to elucidate the mechanism(s) underlying these phenomena by intercrossing apoC3(-/-) mice with apoE(-/-) mice to study the effects of apoC-III deficiency against a hyperlipidemic background. Similar to apoE(+/+) apoC3(-/-) mice, apoE(-/-)apoC3(-/-) mice exhibited a marked reduction in VLDL cholesterol and TG, indicating that the mechanism(s) by which apoC-III deficiency exerts its lipid-lowering effect act independent of apoE. On both backgrounds, apoC3(-/-) mice showed normal intestinal lipid absorption and hepatic VLDL TG secretion. However, turnover studies showed that TG-labeled emulsion particles were cleared much more rapidly in apoC3(-/-) mice, whereas the clearance of VLDL apoB, as a marker for whole particle uptake by the liver, was not affected. Furthermore, it was shown that cholesteryl oleate-labeled particles were also cleared faster in apoC3(-/-) mice. Thus the mechanisms underlying the hypolipidemia in apoC3(-/-) mice involve both a more efficient hydrolysis of VLDL TG as well as an enhanced selective clearance of VLDL cholesteryl esters from plasma. In summary, our studies of apoC3(-/-) mice support the concept that apoC-III is an effective inhibitor of VLDL TG hydrolysis and reveal a potential regulating role for apoC-III with respect to the selective uptake of cholesteryl esters. Show less