👤 Susanna Brauner

Systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) are autoimmune disorders characterized by autoantibodies, dysregulated B cells, and notably high female-to-male incidence ratios. Genome-wide association studies have identified several susceptibility SNPs for both diseases. Many SNPs in the genome are expression quantitative trait loci (eQTLs), with context-dependent effects. Assuming that sex is a biological context, we investigated whether SLE/pSS SNPs act as eQTLs in B cells and used a disease-targeted approach to understand if they display sex-specific effects. We used genome-wide genotype and gene expression data from primary B cells from 125 males and 162 females. The MatrixEQTL R package was used to identify eQTLs within a genomic window of 2 Mb centered on each of 22 established SLE and/or pSS susceptibility SNPs. To find sex-specific eQTLs, we used a linear model with a SNP * sex interaction term. We found ten SNPs affecting the expression of 16 different genes (FDR < 0.05). rs7574865-INPP1, rs7574865-MYO1B, rs4938573-CD3D, rs11755393-SNRPC, and rs4963128-PHRF1 were novel observations for the immune compartment and B cells. By analyzing the SNP * sex interaction terms, we identified six genes with differentially regulated expression in females compared to males, depending on the genotype of SLE/pSS-associated SNPs: SLC39A8 (BANK1 locus), CD74 (TNIP1 locus), PXK, CTSB (BLK/FAM167A locus), ARCN1 (CXCR5 locus), and DHX9 (NCF2 locus). We identified several unknown sex-specific eQTL effects of SLE/pSS-associated genetic polymorphisms and provide novel insight into how gene-sex interactions may contribute to the sex bias in systemic autoimmune diseases. Show less

Phytosterol-enriched foods are increasingly marketed to lower cholesterol levels and atherosclerosis in the general population. Phytosterols reduce cholesterol absorption, but the molecular mechanism is controversial. We therefore investigated the phytosterol effects on cholesterol metabolism in human enterocyte, hepatocyte, and macrophage models relevant for sterol absorption, reverse transport, and excretion. Isomolar sitosterol (50 μmol/L) was less effectively taken up by enterocytes than cholesterol but suppressed apical cholesterol uptake by 50% (P < 0.01) and basolateral secretion by two-thirds (P < 0.01) whether added in micelles or ethanol or complexed to cyclodextrin. In contrast, enterocytes handled nanomolar (3)H-sitosterol similarly to cholesterol. Enterocytes selectively oxidized all sterols to 27-hydroxy- and 27-carboxy-sterols. Conversion rates were much lower for sitosterol (0.05 ± 0.02 nmol/mg protein) and campesterol (0.48 ± 0.10) compared with cholesterol (3.73 ± 0.60) (P < 0.001). 27-Hydroxycholesterol (27OH-C) activated liver-X-receptor alpha (LXRα) (P < 0.01) and stimulated ATP-binding cassette transporter (ABC) A1 expression (P < 0.001) and basolateral systemic cholesterol secretion from enterocytes (P < 0.05). In co-incubations, phytosterols inhibited 27OH-C generation by sterol 27-hydroxylase (P < 0.001) and reduced LXRα-mediated ABCA1 expression (P < 0.01) and basolateral systemic cholesterol secretion. In contrast, ABCG8 transcription and apical sterol resecretion was unchanged by LXRα activation in human enterocytes. Exogenous LXRα agonists reverted sterol selectivity and phytosterol cholesterol interaction. Due to constitutive apical expression of ABCG5/G8 and LXRα-enhanced basolateral expression of ABCA1 in enterocytes, interference of phytosterols with the generation of the dominating LXRα-agonist 27OH-C blocks the self-priming component of cholesterol absorption. This local LXRα antagonism of dietary phytosterols contributes to sterol selectivity and reduces fractional cholesterol absorption and preloading of nascent HDL with dietary cholesterol. Show less