👤 Jenny A Visser

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

Cerebrospinal fluid amyloid beta 42, total tau, and phosphorylated tau 181 are well accepted markers of Alzheimer's disease. These biomarkers better reflect disease pathogenesis compared to clinical diagnosis. Here, we perform a genome wide association study meta-analysis including 18,948 individuals of European ancestry and identify 12 genome-wide significant loci across all three biomarkers, eight of them novel. We replicate the association of biomarkers with APOE, CR1, GMNC/CCDC50 and C16orf95/MAP1LC3B. Novel loci include BIN1 for amyloid beta and GNA12, MS4A6A, SLCO1A2 with both total tau and phosphorylated tau 181, as well as additional loci on chr. 8, near ANGPT1 and chr. 9 near SMARCA2. We also demonstrate that these variants have significant association with Alzheimer's disease risk, disease progression and/or brain amyloidosis. The associated genes are implicated in lipid metabolism independent of APOE, coupled with autophagy and brain volume regulation driven by total tau and phosphorylated tau 181 dysregulation. Show less

Chylomicron biosynthesis plays a vital role in supplying essential lipids and lipid soluble vitamins to peripheral tissues for various functions. Despite this, the intracellular synthesis, trafficking, and secretion of chylomicrons remains only partly understood. The purpose of this review is to summarize the role of established proteins in this process and bring attention to recently identified proteins to provide an up-to-date model of chylomicron biosynthesis. Recently, several proteins have been shown to play a role in the initial formation and lipidation of chylomicrons at the endoplasmic reticulum (ER), which include: TM6SF2, PLA2G12B, PRAP1, and SURF4. In addition, mitochondria have been implicated in chylomicron metabolism, but mechanistic insight is missing. The trafficking of chylomicrons from the ER to the Golgi, and the subsequent trafficking from the Golgi to the basolateral side of enterocytes, however, remains a mystery. Progress in the chylomicron biosynthesis field is largely associated with findings in VLDL biosynthesis. In addition, increased insight in events after prechylomicrons leave the ER is needed. Given the important role of chylomicron biosynthesis in whole-body lipid metabolism, further research into the molecular mechanisms is warranted. Show less

Protein truncating variants (PTVs) in To identify high-priority missense variants (HPVs), we applied ‘domain mapping of disease mutations’ for the 637 unique coding In this sample, PTVs and HPVs associated with respectively a 35- and 10-fold increased risk of early onset AD and 17- and 6-fold increased risk of overall AD. The median age at onset (AAO) of PTV- and HPV-carriers was 62 and 64 years, and Our results justify a debate on whether HPV carriers should be considered for clinical counseling. The online version contains supplementary material available at 10.1186/s13024-025-00907-z. Show less

The Carbohydrate Response Element Binding Protein (ChREBP) is a glucose-responsive transcription factor (TF) with two major splice isoforms (α and β). In chronic hyperglycemia and glucolipotoxicity, ChREBPα-mediated ChREBPβ expression surges, leading to insulin-secreting β-cell dedifferentiation and death. 14-3-3 binding to ChREBPα results in cytoplasmic retention and suppression of transcriptional activity. Thus, small molecule-mediated stabilization of this protein-protein interaction (PPI) may be of therapeutic value. Here, we show that structure-based optimizations of a 'molecular glue' compound led to potent ChREBPα/14-3-3 PPI stabilizers with cellular activity. In primary human β-cells, the most active compound retained ChREBPα in the cytoplasm, and efficiently protected β-cells from glucolipotoxicity while maintaining β-cell identity. This study may thus not only provide the basis for the development of a unique class of compounds for the treatment of Type 2 Diabetes but also showcases an alternative 'molecular glue' approach for achieving small molecule control of notoriously difficult to target TFs. Show less

The melanocortin-4 receptor (MC4R) plays an important role in body weight regulation. Pathogenic MC4R variants are the most common cause of monogenic obesity. We have identified 17 MC4R variants in adult and pediatric patients with obesity. Here we aimed to functionally characterize these variants by analyzing 4 different aspects of MC4R signaling. In addition, we aimed to analyze the effect of setmelanotide, a potent MC4R agonist, on these MC4R variants. Cell surface expression and α-melanocyte stimulating hormone (α-MSH)- or setmelanotide-induced cAMP response, β-arrestin-2 recruitment, and ERK activation were measured in cells expressing either wild type or variant MC4R. We found a large heterogeneity in the function of these variants. We identified variants with a loss of response for all studied MC4R signaling, variants with no cAMP accumulation or ERK activation but normal β-arrestin-2 recruitment, and variants with normal cAMP accumulation and ERK activation but decreased β-arrestin-2 recruitment, indicating disrupted desensitization and signaling mechanisms. Setmelanotide displayed a greater potency and similar efficacy as α-MSH and induced significantly increased maximal cAMP responses of several variants compared to α-MSH. Despite the heterogeneity in functional response, there was no apparent difference in the obesity phenotype in our patients. We show that these obesity-associated MC4R variants affect MC4R signaling differently yet lead to a comparable clinical phenotype. Our results demonstrate the clinical importance of assessing the effect of MC4R variants on a range of molecular signaling mechanisms to determine their association with obesity, which may aid in improving personalized treatment. Show less

The small intestine plays a central role in lipid metabolism, most notably the uptake of dietary fats that are packaged into chylomicrons and secreted into the circulation for utilisation by peripheral tissues. While microsomal triglyceride transfer protein (MTP) is known to play a key role in this pathway, the intracellular assembly, trafficking, and secretion of chylomicrons is incompletely understood. Using human transcriptome datasets to find genes co-regulated with MTTP, we identified ERICH4 as a top hit. The gene encodes for glutamate-rich protein 4, a protein of unknown function. REACTOME gene-function prediction tools indicated that ERICH4 is involved in intestinal lipid metabolism. In addition, GWAS data point to a strong relationship between ERICH4 and plasma lipids. To validate ERICH4 as a lipid gene, we generated whole-body Erich4 knockout (Erich4 Despite prediction tools indicating ERICH4 as a strong candidate gene in intestinal lipid metabolism, we here show that ERICH4 does not play a role in intestinal lipid metabolism in mice. It remains to be established whether ERICH4 plays a role in human lipid metabolism. Show less

Cerebrospinal fluid (CSF) β-site amyloid precursor protein cleaving enzyme 1 (BACE1), neurogranin and the neurogranin/BACE1 ratio are proposed markers for Alzheimer's disease. BACE1 is also a drug target. However, CSF levels may differ between early-stage amyloid plaque formation (A) and later stage downstream tau-tangle pathology (T) and neurodegeneration (N) and may be expressed as an A/T/N stage (e.g. A+/T-/N or A+/T+/N+). Whether BACE1 and neurogranin levels are persistent traits or change with disease progression is unknown. The aim of this study was to investigate whether CSF neurogranin and BACE1 concentrations differ between A/T/N stages, whether these change over time and correlate with memory decline. This may have implications for patient selection in future trials. We used CSF markers to determine A/T/N stage using amyloid beta42/40 ratio, p-tau181 and total-tau respectively in predementia Alzheimer's disease cases ( Show less

We previously identified four Alzheimer's disease (AD) subgroups with increasingly higher cerebrospinal fluid (CSF) levels of tau phosphorylated at threonine 181 (p-tau). These subgroups included individuals across the cognitive spectrum, suggesting p-tau subgroups could reflect distinct biological changes in AD, rather than disease severity. Therefore, in the current study, we further investigated which potential processes may be related with p-tau subgroups, by comparing individuals on CSF markers for presynaptic structure [vesicle-associated membrane protein 2 (VAMP2)], postsynaptic structure [neurogranin (NRGN)], axonal damage [neurofilament light (NfL)], and amyloid production [beta-secretase 1 (BACE1) and amyloid-beta 1-40 (Aβ40)]. We selected 348 amyloid-positive (A+) individuals (53 preclinical, 102 prodromal, 193 AD dementia) and 112 amyloid-negative (A-) cognitively normal (CN) individuals from the Amsterdam Dementia Cohort (ADC). Individuals were labeled according to their p-tau subgroup (subgroup 1: p-tau ≤ 56 pg/ml; subgroup 2: 57-96 pg/ml; subgroup 3: 97-159 pg/ml; subgroup 4: > 159 pg/ml). CSF protein levels were measured with ELISA (NRGN, BACE1, Aβ40, NfL) or single-molecule array (Simoa) (VAMP2). We tested whether protein levels differed between the p-tau subgroups within A+ individuals with linear models corrected for age and sex and whether disease stage influenced these relationships. Among A+ individuals, higher p-tau subgroups showed a higher percentage of AD dementia [subgroup 1: n = 41/94 (44%); subgroup 2: n = 81/147 (55%); subgroup 3: n = 59/89 (66%); subgroup 4: n = 7/11 (64%)]. Relative to controls, subgroup 1 showed reduced CSF levels of BACE1, Aβ40, and VAMP2 and higher levels of NfL. Subgroups 2 to 4 showed gradually increased CSF levels of all measured proteins, either across the first three (NfL and Aβ40) or across all subgroups (VAMP2, NRGN, BACE1). The associations did not depend on the clinical stage (interaction p-values ranging between 0.19 and 0.87). The results suggest that biological heterogeneity in p-tau levels in AD is related to amyloid metabolism and synaptic integrity independent of clinical stage. Biomarkers reflecting amyloid metabolism and synaptic integrity may be useful outcome measures in clinical trials targeting tau pathology. Show less

The systematic stabilization of protein-protein interactions (PPI) has great potential as innovative drug discovery strategy to target novel and hard-to-drug protein classes. The current lack of chemical starting points and focused screening opportunities limits the identification of small molecule stabilizers that engage two proteins simultaneously. Starting from our previously described virtual screening strategy to identify inhibitors of 14-3-3 proteins, we report a conceptual molecular docking approach providing concrete entries for discovery and rational optimization of stabilizers for the interaction of 14-3-3 with the carbohydrate-response element-binding protein (ChREBP). X-ray crystallography reveals a distinct difference in the binding modes between weak and general inhibitors of 14-3-3 complexes and a specific, potent stabilizer of the 14-3-3/ChREBP complex. Structure-guided stabilizer optimization results in selective, up to 26-fold enhancement of the 14-3-3/ChREBP interaction. This study demonstrates the potential of rational design approaches for the development of selective PPI stabilizers starting from weak, promiscuous PPI inhibitors. Show less

Fluoxetine is a selective serotonin reuptake inhibitor and long-lived open channel blocker of the acetylcholine receptor, often used in the treatment of slow-channel congenital myasthenic syndromes (CMS). We report a 42-year-old woman who had a history of episodic limb weakness that worsened after initiation of fluoxetine for treatment of depression. Genetic testing for CMS revealed a homozygous pathogenic mutation in the rapsyn (RAPSN) gene (p.Asn88Lys). Electrodiagnostic testing was performed before and 1 month after discontinuation of fluoxetine. The 2 Hz repetitive nerve stimulation of the fibular and spinal accessory nerves showed a baseline decrement of 36% and 14%, respectively. One month after discontinuing fluoxetine, the spinal accessory nerve decrement was no longer present, and the decrement in the fibular nerve was improved at 17%. This case demonstrates worsening of both clinical and electrophysiologic findings in a patient with CMS secondary to a RAPSN mutation treated with fluoxetine. Muscle Nerve 55: 131-135, 2017. Show less

The severe forms of hypertriglyceridaemia (HTG) are caused by mutations in genes that lead to the loss of function of lipoprotein lipase (LPL). In most patients with severe HTG (TG > 10 mmol L(-1) ), it is a challenge to define the underlying cause. We investigated the molecular basis of severe HTG in patients referred to the Lipid Clinic at the Academic Medical Center Amsterdam. The coding regions of LPL, APOC2, APOA5 and two novel genes, lipase maturation factor 1 (LMF1) and GPI-anchored high-density lipoprotein (HDL)-binding protein 1 (GPIHBP1), were sequenced in 86 patients with type 1 and type 5 HTG and 327 controls. In 46 patients (54%), rare DNA sequence variants were identified, comprising variants in LPL (n = 19), APOC2 (n = 1), APOA5 (n = 2), GPIHBP1 (n = 3) and LMF1 (n = 8). In 22 patients (26%), only common variants in LPL (p.Asp36Asn, p.Asn318Ser and p.Ser474Ter) and APOA5 (p.Ser19Trp) could be identified, whereas no mutations were found in 18 patients (21%). In vitro validation revealed that the mutations in LMF1 were not associated with compromised LPL function. Consistent with this, five of the eight LMF1 variants were also found in controls and therefore cannot account for the observed phenotype. The prevalence of mutations in LPL was 34% and mostly restricted to patients with type 1 HTG. Mutations in GPIHBP1 (n = 3), APOC2 (n = 1) and APOA5 (n = 2) were rare but the associated clinical phenotype was severe. Routine sequencing of candidate genes in severe HTG has improved our understanding of the molecular basis of this phenotype associated with acute pancreatitis and may help to guide future individualized therapeutic strategies. Show less

Genome-wide association studies (GWAS) have identified multiple loci associated with plasma lipid concentrations. Common variants at these loci together explain <10% of variation in each lipid trait. Rare variants with large individual effects may also contribute to the heritability of lipid traits; however, the extent to which rare variants affect lipid phenotypes remains to be determined. Here we show an accumulation of rare variants, or a mutation skew, in GWAS-identified genes in individuals with hypertriglyceridemia (HTG). Through GWAS, we identified common variants in APOA5, GCKR, LPL and APOB associated with HTG. Resequencing of these genes revealed a significant burden of 154 rare missense or nonsense variants in 438 individuals with HTG, compared to 53 variants in 327 controls (P = 6.2 x 10(-8)), corresponding to a carrier frequency of 28.1% of affected individuals and 15.3% of controls (P = 2.6 x 10(-5)). Considering rare variants in these genes incrementally increased the proportion of genetic variation contributing to HTG. Show less

To identify loci for age at menarche, we performed a meta-analysis of 32 genome-wide association studies in 87,802 women of European descent, with replication in up to 14,731 women. In addition to the known loci at LIN28B (P = 5.4 × 10⁻⁶⁰) and 9q31.2 (P = 2.2 × 10⁻³³), we identified 30 new menarche loci (all P < 5 × 10⁻⁸) and found suggestive evidence for a further 10 loci (P < 1.9 × 10⁻⁶). The new loci included four previously associated with body mass index (in or near FTO, SEC16B, TRA2B and TMEM18), three in or near other genes implicated in energy homeostasis (BSX, CRTC1 and MCHR2) and three in or near genes implicated in hormonal regulation (INHBA, PCSK2 and RXRG). Ingenuity and gene-set enrichment pathway analyses identified coenzyme A and fatty acid biosynthesis as biological processes related to menarche timing. Show less