👤 Jan M Prins

Melanocortin-2 receptor accessory protein-2 (MRAP2) modulates the activity of hypothalamic melanocortin-4 (MC4R) and growth hormone-secretagogue (GHSR) receptors, which suppress and promote appetite, respectively. We investigate whether obesity-associated variants of MRAP2 alter their ability to modulate MC4R and GHSR signalling as a possible mechanistic link to the development of obesity. Functional effects of five obesity-associated MRAP2 variants were analysed in HEK293 cells by co-expressing wild-type or variant MRAP2 with MC4R or GHSR. Endpoints included cell-surface and total expression, and ligand-induced second-messenger responses, β-arrestin-2 recruitment, and alternative G-protein activation. MRAP2 decreased basal MC4R cell-surface expression while GHSR cell-surface expression was not affected. In MC4R/MRAP2 expressing cells, maximal α-MSH-induced cAMP and β-arrestin-2 recruitment responses were increased. Similarly, ghrelin-induced Ca2+-mobilization in GHSR/MRAP2 expressing cells was increased, but β-arrestin-2 recruitment was suppressed. MRAP2 did not bias G-protein activation by either receptor, although previous reports show MRAP2 biases MC4R signalling towards Gαq/11. The variants did not significantly affect the ability of MRAP2 to modulate MC4R and GHSR signalling. Our results indicate that MRAP2 potentiates the ligand responsiveness of MC4R and GHSR, but has differential effects on β-arrestin-2 recruitment. The MRAP2 variants had no significant effects on the signalling endpoints tested. This suggests that, despite their association with obesity, the variants may be functionally benign, or that the absence of effects reflects limitations inherent to our cellular model. In addition, since MRAP2 can modulate multiple receptors and differentially modulate their signalling, we cannot rule out their influence on body weight regulation via other mechanisms. Show less

Sufficient physical activity has the potential to mitigate the late effects of cancer, but objective data of activity levels in patients after pediatric bone cancer are scarce. This study aimed to objectively assess physical activity levels in this population and explore differences based on patient- and treatment-related factors. As part of a cross-sectional study of a nationwide cohort of patients treated for pediatric bone sarcoma, we assessed physical activity using an accelerometer, the ActiGraph GT9X Link. Physical intensity levels were categorized as sedentary, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA) and compared between subgroups stratified by sex, age, tumor location, type of surgery for tumors around the knee, and time since local therapy. Among 79 participants, 47% were female, and median age at evaluation was 19.8 years (IQR 17.5-23.9) with a median of 5.9 years (IQR 2.9-11.7) since local therapy. Mean daily sedentary time was 643 min (SD = 104), 127 min per day (SD = 58) was spent in LPA, and 63 min per day (SD = 35) in MVPA. Seventy-eight percent of participants met the World Health Organization's recommended level of MVPA. No significant differences in intensity levels were found between the various subgroups. Pediatric bone sarcoma patients seem to regain participation in higher-intensity activities post-treatment, with physical activity levels comparable to the general population. No surgical approach is superior in terms of physical activity. Implications for Cancer Survivors Shared decision-making is important in guiding the choice of local therapy and should be informed by lifestyle and individual preferences. High sedentary time suggests scope for improvement in survivorship care. Show less

Persistent monocyte activation and altered cytokine responses are reported in PWH despite ART. How prior HIV-1 infection status and timing of ART initiation relate to monocyte pattern-recognition receptor crosstalk between TLR8 and RLRs remains uncertain. We conducted a comparative cohort study in adult males enrolled from two Dutch HIV-cohorts. Participants included HIV-negative participants, PWH who initiated ART during chronic HIV infection, and PWH who initiated ART during acute HIV infection, with sampling at 24 and 156 weeks after ART initiation for the acute group. PBMCs were stimulated with an RLR agonist, a TLR8 agonist, or both. Monocyte surface markers were assessed by flow cytometry and pro-inflammatory cytokines were analysed with qPCR and ELISA. Across groups, RLR stimulation induced IL-12p70 and IL-27, TLR8 stimulation induced IL-6 and IL-12p70 and combined TLR8 + RLR co-stimulation synergistically increased IL-12p70 and IL-27 while restricting IL-6. Compared with controls, CHI showed reduced IL-12p70 and IL-27 and higher IL-6. In AHI at 24 weeks, cytokine patterns and co-stimulation effects resembled HIV-negative participants; by 156 weeks, responses were attenuated and approximated CHI. In this male cohort, TLR8-RLR crosstalk was preserved early after ART initiation during acute infection but diminished over time, approaching profiles observed in chronically treated infection. These observations emphasise a potential early window after ART initiation for interventions aiming to preserve monocyte function and motivate studies to characterise underlying mechanisms. Funding for this study was obtained through a ZonMW/Aidsfonds grant NL4Cure: Bridging shock and kill strategies (446002508). Show less

Concentrations of liver enzymes in plasma are widely used as indicators of liver disease. We carried out a genome-wide association study in 61,089 individuals, identifying 42 loci associated with concentrations of liver enzymes in plasma, of which 32 are new associations (P = 10(-8) to P = 10(-190)). We used functional genomic approaches including metabonomic profiling and gene expression analyses to identify probable candidate genes at these regions. We identified 69 candidate genes, including genes involved in biliary transport (ATP8B1 and ABCB11), glucose, carbohydrate and lipid metabolism (FADS1, FADS2, GCKR, JMJD1C, HNF1A, MLXIPL, PNPLA3, PPP1R3B, SLC2A2 and TRIB1), glycoprotein biosynthesis and cell surface glycobiology (ABO, ASGR1, FUT2, GPLD1 and ST3GAL4), inflammation and immunity (CD276, CDH6, GCKR, HNF1A, HPR, ITGA1, RORA and STAT4) and glutathione metabolism (GSTT1, GSTT2 and GGT), as well as several genes of uncertain or unknown function (including ABHD12, EFHD1, EFNA1, EPHA2, MICAL3 and ZNF827). Our results provide new insight into genetic mechanisms and pathways influencing markers of liver function. Show less

Primary cilia are specialized cell surface projections found on most cell types. Involved in several signaling pathways, primary cilia have been reported to modulate cell and tissue organization. Although they have been implicated in regulating cartilage and bone growth, little is known about the organization of primary cilia in the growth plate cartilage and osteochondroma. Osteochondromas are bone tumors formed along the growth plate, and they are caused by mutations in EXT1 or EXT2 genes. In this study, we show the organization of primary cilia within and between the zones of the growth plate and osteochondroma. Using confocal and electron microscopy, we found that in both tissues, primary cilia have a similar formation but a distinct organization. The shortest ciliary length is associated with the proliferative state of the cells, as confirmed by Ki-67 immunostaining. Primary cilia organization in the growth plate showed that non-polarized chondrocytes (resting zone) are becoming polarized (proliferating and hypertrophic zones), orienting the primary cilia parallel to the longitudinal axis of the bone. The alignment of primary cilia forms one virtual axis that crosses the center of the columns of chondrocytes reflecting the polarity axis of the growth plate. We also show that primary cilia in osteochondromas are found randomly located on the cell surface. Strikingly, the growth plate-like polarity was retained in sub-populations of osteochondroma cells that were organized into small columns. Based on this, we propose the existence of a mixture ('mosaic') of normal lining (EXT(+/-) or EXT(wt/wt)) and EXT(-/-) cells in the cartilaginous cap of osteochondromas. Show less