Study of the 5-HT4 receptor/ADAM10/APP complex and search for proteins associated with ADAM10 : new players promoting the non-amyloidogenic pathway in the context of Alzheimer’s disease

La protéine précurseur du peptide amyloïde (APP) est un élément central dans l'apparition et le développement de la maladie d'Alzheimer. L'APP possède deux voies de maturations distinctes. La maturation dite amyloïdogénique, via la béta-sécrétase, a principalement lieu au niveau des endosomes et entraine la production de peptides béta-amyloïdes neurotoxiques au-delà d'un certain seuil. La voie non-amyloïdogénique, via l'alpha-sécrétase, a quant à elle lieu au niveau de la membrane plasmique et entraîne la libération de fragments solubles sAPP alpha; neuroprotecteurs. Dans un premier temps, nos travaux ont mis en évidence que le récepteur de la sérotonine de type 4 (5-HT4R), l'alpha-sécrétase ADAM10 et l'APP forment un complexe protéique et que le récepteur 5-HT4 est capable de moduler à la fois l'adressage membranaire de l'alpha-sécrétase ADAM10 et de l'APP mais aussi leur maturation. Par cette modulation, le récepteur 5-HT4 peut favoriser de façon constitutive la libération de sAPP alpha. Dans un second temps, nous avons mis en place une approche protéomique, basée sur la recherche de protéines interagissant avec ce complexe et pouvant influencer le trafic cellulaire de l'ADAM10 ou de l'APP et favoriser la voie non-amyloïdogénique. Ces travaux nous permettent d'émettre des hypothèses originales quant aux mécanismes communs de régulation, à la fois de l'endocytose et du trafic du récepteur 5-HT4, de l'ADAM10 et de l'APP. Ces mécanismes mettent en cause le complexe AP-2 et un autre complexe protéique impliqué dans le trafic intracellulaire du précurseur de la protéine amyloïde.The amyloid precursor protein (APP) is the key element in the appearance and the development of Alzheimer's disease (AD). Basically, APP can be processed following two maturation pathways. The fist one, named the amyloidogenic pathway, involves a secretase, occurs mostly in the endosomes and leads to the release ofbeta-amyloïd peptides that are neurotoxics if overproduced. The second one, named the non-amyloidogenic pathway, involves analpha-secretase, occurs mostly at the plasma membrane and leads to the release of soluble APP alpha fragments that are neuroprotective. First, our work demonstrated that a serotonin receptor, the 5-HT4 receptor (5-HT4R), is able to form a protein complex with the alpha-secretase ADAM10 and APP and that this receptor could modulate ADAM10 and APP trafficking and maturation. By this way, the 5-HT4 receptor is able to increase ADAM10 and APP cell surface localization and to constitutively promote sAPP alpha release. In a second time, using an unbiased proteomic approach, we focused on the quest of protein partners able to interact with this complex and to promote the non-amyloïdogenic pathway. This work allowed us to propose original hypothesis about shared mechanisms able to regulate 5-HT4R, APP and ADAM10 endocytosis and trafficking. These mechanisms involve the AP-2 complex and another protein complex involved in the cellular trafficking of the amyloid precursor protein

Serotonin type 4 receptor dimers

Chapitre 7International audienceNumerous class A G protein-coupled receptors and especially biogenic amine receptors have been reported to form homodimers. Indeed, the dimerization process might occur for all the metabotropic serotonergic receptors. Moreover, dimerization appears to be essential for the function of serotonin type 2C (5-HT2C) and type 4 (5-HT4) receptors and required to obtain full receptor activity. Several techniques have been developed to analyze dimer formation and properties. Due to our involvement in deciphering 5-HT4R transduction mechanisms, we improved and set up new procedures to study 5-HT4R dimers, by classical methods or modern tools. This chapter presents detailed protocols to detect 5-HT4R dimers by western blotting and co-immunoprecipitation, including the optimizations that we routinely carry out. We developed an innovative method to achieve functional visualization of 5-HT4R dimers by immunofluorescence, taking advantage of the 5-HT4-RASSL (Receptor Activated Solely by Synthetic Ligand) mutant that was engineered in the laboratory. Finally, we adapted the powerful Time-resolved FRET technology to assess a relative quantification of dimer formation and affinit

Alzheimer culprits: cellular crossroads and interplay

International audienceAlzheimer's disease (AD) is the primary cause of dementia in the elderly and one of the major health problems worldwide. Since its first description by Alois Alzheimer in 1907, noticeable but insufficient scientific comprehension of this complex pathology have been achieved. All the research that has been pursued takes origin from the identification of the pathological hallmarks in the forms of amyloid-b (Ab) deposits (plaques), and aggregated hyperphosphorylated tau protein filaments (named neurofibrillary tangles). Since this discovery, many hypotheses have been proposed to explain the origin of the pathology. The "amyloid cascade hypothesis" is the most accredited theory. The mechanism suggested to be one of the initial causes of AD is an imbalance between the production and the clearance of Ab peptides. Therefore, Amyloid Precursor Protein (APP) synthesis, trafficking and metabolism producing either the toxic Ab peptide via the amyloidogenic pathway or the sAPPa fragment via the non amyloidogenic pathway have become appealing subjects of study. Being able to reduce the formation of the toxic Ab peptides is obviously an immediate approach in the trial to prevent AD. The following review summarizes the most relevant discoveries in the field of the last decades

5-HT 4 Receptors Constitutively Promote the Non-Amyloidogenic Pathway of APP Cleavage and Interact with ADAM10

International audienceIn addition to the amyloidogenic pathway, amyloid precursor protein (APP) can be cleaved by α-secretases, producing soluble and neuroprotective APP alpha (sAPPα) (nonamyloidogenic pathway) and thus preventing the generation of pathogenic amyloid-β. However, the mechanisms regulating APP cleavage by α-secretases remain poorly understood. Here, we showed that expression of serotonin type 4 receptors (5-HT(4)Rs) constitutively (without agonist stimulation) induced APP cleavage by the α-secretase ADAM10 and the release of neuroprotective sAPPα in HEK-293 cells and cortical neurons. This effect was independent of cAMP production. Interestingly, we demonstrated that 5-HT(4) receptors physically interacted with the mature form of ADAM10. Stimulation of 5-HT(4) receptors by an agonist further increased sAPPα secretion, and this effect was mediated by cAMP/Epac signaling. These findings describe a new mechanism whereby a GPCR constitutively stimulates the cleavage of APP by α-secretase and promotes the nonamyloidogenic pathway of APP processing

5‑HT₄ Receptors Constitutively Promote the Non-Amyloidogenic Pathway of APP Cleavage and Interact with ADAM10

In addition to the amyloidogenic pathway, amyloid precursor protein (APP) can be cleaved by α-secretases, producing soluble and neuroprotective APP alpha (sAPPα) (nonamyloidogenic pathway) and thus preventing the generation of pathogenic amyloid-β. However, the mechanisms regulating APP cleavage by α-secretases remain poorly understood. Here, we showed that expression of serotonin type 4 receptors (5-HT₄Rs) constitutively (without agonist stimulation) induced APP cleavage by the α-secretase ADAM10 and the release of neuroprotective sAPPα in HEK-293 cells and cortical neurons. This effect was independent of cAMP production. Interestingly, we demonstrated that 5-HT₄ receptors physically interacted with the mature form of ADAM10. Stimulation of 5-HT₄ receptors by an agonist further increased sAPPα secretion, and this effect was mediated by cAMP/Epac signaling. These findings describe a new mechanism whereby a GPCR constitutively stimulates the cleavage of APP by α-secretase and promotes the nonamyloidogenic pathway of APP processing

5-HT 4

[Image: see text] In addition to the amyloidogenic pathway, amyloid precursor protein (APP) can be cleaved by α-secretases, producing soluble and neuroprotective APP alpha (sAPPα) (nonamyloidogenic pathway) and thus preventing the generation of pathogenic amyloid-β. However, the mechanisms regulating APP cleavage by α-secretases remain poorly understood. Here, we showed that expression of serotonin type 4 receptors (5-HT(4)Rs) constitutively (without agonist stimulation) induced APP cleavage by the α-secretase ADAM10 and the release of neuroprotective sAPPα in HEK-293 cells and cortical neurons. This effect was independent of cAMP production. Interestingly, we demonstrated that 5-HT(4) receptors physically interacted with the mature form of ADAM10. Stimulation of 5-HT(4) receptors by an agonist further increased sAPPα secretion, and this effect was mediated by cAMP/Epac signaling. These findings describe a new mechanism whereby a GPCR constitutively stimulates the cleavage of APP by α-secretase and promotes the nonamyloidogenic pathway of APP processing

Correction: Rare predicted loss-of-function variants of type I IFN immunity genes are associated with life-threatening COVID-19

International audienc

Rare predicted loss-of-function variants of type I IFN immunity genes are associated with life-threatening COVID-19

BackgroundWe previously reported that impaired type I IFN activity, due to inborn errors of TLR3- and TLR7-dependent type I interferon (IFN) immunity or to autoantibodies against type I IFN, account for 15-20% of cases of life-threatening COVID-19 in unvaccinated patients. Therefore, the determinants of life-threatening COVID-19 remain to be identified in similar to 80% of cases.MethodsWe report here a genome-wide rare variant burden association analysis in 3269 unvaccinated patients with life-threatening COVID-19, and 1373 unvaccinated SARS-CoV-2-infected individuals without pneumonia. Among the 928 patients tested for autoantibodies against type I IFN, a quarter (234) were positive and were excluded.ResultsNo gene reached genome-wide significance. Under a recessive model, the most significant gene with at-risk variants was TLR7, with an OR of 27.68 (95%CI 1.5-528.7, P=1.1x10(-4)) for biochemically loss-of-function (bLOF) variants. We replicated the enrichment in rare predicted LOF (pLOF) variants at 13 influenza susceptibility loci involved in TLR3-dependent type I IFN immunity (OR=3.70[95%CI 1.3-8.2], P=2.1x10(-4)). This enrichment was further strengthened by (1) adding the recently reported TYK2 and TLR7 COVID-19 loci, particularly under a recessive model (OR=19.65[95%CI 2.1-2635.4], P=3.4x10(-3)), and (2) considering as pLOF branchpoint variants with potentially strong impacts on splicing among the 15 loci (OR=4.40[9%CI 2.3-8.4], P=7.7x10(-8)). Finally, the patients with pLOF/bLOF variants at these 15 loci were significantly younger (mean age [SD]=43.3 [20.3] years) than the other patients (56.0 [17.3] years; P=1.68x10(-5)).ConclusionsRare variants of TLR3- and TLR7-dependent type I IFN immunity genes can underlie life-threatening COVID-19, particularly with recessive inheritance, in patients under 60 years old