Non-cell autonomous inhibition of the Shh pathway due to impaired cholesterol biosynthesis requires Ptch1/2

Birth defects due to congenital errors in enzymes involved cholesterol synthesis like Smith-Lemli-Opitz syndrome (SLOS) and Lathosterolosis cause an accumulation of cholesterol precursors and a deficit in cholesterol. The phenotype of both SLOS and Lathosterolosis have similarities to syndromes associated with abnormal Sonic hedgehog (Shh) signaling, consistent with the notion that impaired cholesterol signaling can cause reduced Shh signaling. Two multipass membrane proteins play central roles in Shh signal transduction, the putative Resistance, Nodulation and Division (RND) antiporters Ptch1 and Ptch2, and the G-protein coupled receptor Smoothened (Smo). Sterols have been suggested as cargo for Ptch1, while Smo activity can affected both positively and negatively by steroidal molecules. We demonstrate that mESCs mutant for 7-dehydroxycholesterol reductase (7dhcr) or sterol-C5-desaturase (sc5d) reduce the Hh response in nearby wildtype cells when grown in mosaic organoids. This non-cell autonomous inhibitory activity of the mutant cells required the presence of both Ptch1 and Ptch2. These observations support a model in which late cholesterol precursors that accumulate in cells lacking 7DHCR are the cargo for Ptch1 and Ptch2 activity that mediates the non-cell autonomous inhibition of Smo.

Involvement of 27-Hydroxycholesterol in Mitotane Action on Adrenocortical Carcinoma

Adrenocortical carcinoma (ACC) is a rare cancer with poor prognosis. Mitotane, the standard treatment for ACC, impairs adrenocortical steroid biosynthesis and cholesterol metabolism. In the H295R cell line, a standard ACC in vitro model, mitotane was previously reported to enhance the production of some oxysterols. To verify the possible mechanistic involvement of oxysterols in the anti-ACC effect of mitotane, a gas chromatography mass spectrometry (GC-MS) profiling of oxysterols and the main cholesterol precursors was carried out in H295R cells. Among the oxysterols detected in mitotane-treated cells, 27OHC was markedly produced, as well as lanosterol and lathosterol cholesterol precursors. In this cell model, mitotane was confirmed to affect mitochondrial transmembrane potential and induce apoptosis. Such cytotoxic effects were perfectly matched by H295R cell treatment with a single identical micromolar amount of 27OHC. The mitotane-dependent strong increase in 27OHC was confirmed in vivo, in the plasma of ACC patients under treatment with the drug. Moreover, lanosterol, lathosterol, desmosterol and, to a minor extent, 24-hydroxycholesterol and 25-hydroxycholesterol plasma levels were significantly increased in those patients. The cytotoxic effect of mitotane on ACC cells may be partly related to the increased intracellular level of 27OHC induced by the drug itself.

Active liver X receptor signaling in phagocytes in multiple sclerosis lesions

Objective: We sought to determine the liver X receptor (LXR) ligands present in human macrophages after myelin phagocytosis and whether LXRs are activated in multiple sclerosis (MS) lesions. Methods: We used real-time quantitative polymerase chain reaction (PCR) and immunohistochemistry to determine expression of LXRs and their response genes in human phagocytes after myelin phagocytosis and in active MS lesions. We used gas chromatographic/mass spectrometric analysis to determine LXR-activating oxysterols and cholesterol precursors present and formed in myelin and myelin-incubated cells, respectively. Results: Myelin induced LXR response genes ABCA1 and ABCG1 in human monocyte-derived macrophages. In active MS lesions, we found that both gene expression and protein levels of ABCA1 and apolipoprotein E ( APOE) are upregulated in foamy phagocytes. Moreover, we found that the LXR ligand 27-hydroxycholesterol (27OHC) is significantly increased in human monocyte-derived macrophages after myelin uptake. Conclusion: LXR response genes are upregulated in phagocytes present in active MS lesions, indicating that LXRs are activated in actively demyelinating phagocytes. In addition, we have shown that myelin contains LXR ligands and that 27OHC is generated in human monocyte-derived macrophages after myelin processing. This suggests that LXRs in phagocytes in active MS lesions are activated at least partially by (oxy)sterols present in myelin and the generation thereof during myelin processing.

Oxysterols and cholesterol precursors correlate to magnetic resonance imaging measures of neurodegeneration in multiple sclerosis

Background: Cholesterol homeostasis is important for formation and maintenance of myelin and axonal membranes in the central nervous system (CNS). The concentrations of the brain specific cholesterol metabolite 24S-hydroxycholesterol (24OHC) and cholesterol precursors have been shown to be altered in multiple sclerosis (MS). However, how changes in sterol levels relate to the pathological processes in MS is not clear. Methods: In this study, we compared serum and cerebrospinal fluid (CSF) sterol levels between 105 MS (51 relapsing–remitting (RR); 39 secondary progressive (SP) and 15 primary progressive (PP)) and 49 control patients. Sterol levels were correlated to magnetic resonance imaging (MRI) markers of disease activity. Results: We found decreased serum 24OHC and 27-hydroxycholesterol (27OHC) and increased CSF lathosterol in MS patients compared to control patients ( p=0.018, p=0.002 and p=0.002, respectively). Subgroup analysis showed that serum 24OHC levels were negatively correlated to normalized brain volume measurements in relapse-onset MS patients ( r= −0.326, p=0.004). Conclusions: These results confirm that cholesterol homeostasis is disturbed in MS and suggest that changes in cholesterol synthesis are related to neurodegenerative pathological processes as seen on the MRI. The data seem to be in line with the recently reported observation that high dose statins may have a positive effect on clinical disability in secondary progressive MS.