Murine small intestinal CD103+ dendritic cells (DCs) produce retinoic acid (RA) through retinaldehyde dehydrogenase (RALDH) activity, thereby inducing ‘gut-homing’ α4β7 and CCR9 on T cells they activate, enhancing TGF-β-mediated induction of Foxp3+ regulatory T cells and suppressing induction of pro-inflammatory TH17 cells. RALDH activity of CD103+ DCs is reduced in mouse models of inflammatory bowel disease (IBD) but the role of RALDH activity in human intestinal DCs in the pathogenesis of IBD is undefined. This project aimed to determine the influence of inflammation on RALDH activity of antigen presenting cell (APC) subsets including CD103+ DCs within human distal intestinal mucosa. RALDH activity was identified by Aldefluor assay in intestinal DCs (CD103+ and CD103- subsets) alongside ALDH1A2 expression in healthy controls. In contrast with mouse models, RALDH activity was not reduced in CD103+ DCs from IBD patients. An increased frequency of CD14+ macrophages (MФ) of IBD patients displayed ALDH1A1-associated RALDH activity compared with healthy controls. Blood CD14+ monocytes, putative precursors of intestinal CD14+ MФ, of healthy controls and IBD patients displayed ALDH1A1-associated RALDH activity indicating RALDH is systemically acquired by monocytes and upregulated within the mucosa of IBD patients, or alternatively that RALDH+ monocytes are selectively recruited in IBD. In vitro, inhibition of RA receptor-α signalling blocked GM-CSF-mediated differentiation of TNFα-producing pro-inflammatory RALDH+ CD14+ MФ from monocytes, consistent with enhanced RALDH activity of intestinal CD14+ MФ in IBD supporting a pro-inflammatory phenotype. Soluble intestinal mediators including prostaglandin E2 suppressed RALDH activity of MoDCs in vitro, whilst mediators from inflamed IBD mucosa conditioned MoDCs to imprint enhanced levels of α4β7 expression on naive CD4+ T cells independent of RALDH activity. This study provides the first systematic analysis of RALDH activity in human intestinal APCs and indicates important distinctions between mouse models and human IBD.

Systemic Lupus Erythematosus (SLE) is an autoimmune disease with chronic inflammation affecting multiple organ systems, as well as accelerated atherosclerosis as a major complication. Prior studies by our lab have shown beneficial effects of PPARgamma agonists towards preventing SLE in two different mouse models: the well-established lupus mouse model, MRL.lpr, and the gld.apoE^-/- model of accelerated lupus and atherosclerosis. Retinaldehyde is a retinoic acid precursor that has recently been shown to inhibit PPARgamma signaling in adipose tissue. We proposed that abnormal accumulation of retinaldehyde in lupus promotes autoimmunity by inhibition of PPARgamma signaling. We measured the serum retinaldehyde levels in both lupus mouse models using reversed-phase high-performance liquid chromatography. We also examined the mRNA expressions of genes involved in retinaldehyde metabolism and PPARgamma signaling in white adipose tissues using real-time quantitative PCR. We observed a higher level of circulating retinaldehyde in the MRL.lpr mouse model on a chow diet. The circulating retinaldehyde levels in both .gld.apoE^-/- and C57 increased when maintained on a high-cholesterol Western diet. Within visceral and subcuntaneous adipose tissue, we saw several changes to expression of the genes responsible for retinaldehyde synthesis and catabolism, however further study is required to definitively assess the role of these genes. Importantly, the expression levels of genes involved in PPARgamma signaling decreased in the subcutaneous fat of gld.apoE^-/- mice on a Western diet. Our data suggest that retinaldehyde may play a role in SLE pathogenesis and could be a potential therapeutic target for SLE.

A high frequency of retinitis pigmentosa (RP) is found in Northern Sweden. In an inventory of autosomal recessive RP patients in Västerbotten County, a great number of cases with a unique phenotype was noticed, denoted Bothnia Dystrophy (BD). The aim of the study was to describe the phenotype, to determine the chromosomal location, and to identify the gene. Patients typically show night blindness from early childhood. Symptoms of defect macular function with a decrease of visual acuity can appear in early adulthood. The retinal fundus shows irregular white spots in a central, and parafoveal pattern along the arcades. Centrally areolar maculopathy develops and round circular atrophies are observed in the periphery. The disease was shown to be associated with a missense mutation in the RLBP1 gene resulting in an amino acid substitution (R234W) in the cellular retinaldehyde-binding protein (CRALBP). The R234W mutation was found in a homozygous state in 61 patients affected with BD. Ten patients were heterozygous for the R234W mutation, and presented a similar phenotype. No additional mutations in the coding sequence or exon-intron junctions were found. CRALBP is localised in retinal pigment epithelium (RPE), and Müller cells of the retina. In the RPE, CRALBP functions as a carrier protein for endogenous retinoids. Dark adaptometry and electrophysiologic testing showed an initial loss of rod function followed by a progressive reduction of the cone responses in older ages. A compromised rod function, dysfunction of the Müller cells, and indications of a disturbed function of the inner retina were found. With prolonged dark adaptation, a gradual increase in retinal sensitivity to light and an improvement of the ERG components occurred. The findings indicate a prolonged synthesis of photopigments, retardation of the visual process in the retinal pigment epithelium and a loss of retinal cells probably starting at a relative early age in BD. To evaluate the subjective visual function in BD patients, a battery of objective tests of visual function and composite score of the 25-item NEI-Visual Function Questionnaire (VFQ-25) were analyzed. We found that weighted distance logMAR visual acuity (WVA), had the strongest association with subjective visual function, and that there was a considerable loss of subjective and objective visual function with increasing age in BD patients. The prevalence of BD is as high as 1:3600 in Västerbotten County. The possibility that recycling of retinoids localized in the RPE might be impaired in BD might give future therapeutic possibilities. Due to the large and clinically well-characterized set of patients with this disease, they constitute a suitable study group.