DiDBiT-TMT: A Novel Method to Quantify Changes in the Proteomic Landscape Induced by Neural Plasticity.

Direct detection of biotinylated proteins (DiDBiT) is a proteomic method that can enrich and detect newly synthesized proteins (NSPs) labeled with bio-orthogonal amino acids with 20-fold improved detectability compared to conventional methods. However, DiDBiT has currently been used to compare only two conditions per experiment. Here, we present DiDBiT-TMT, a method that can be used to quantify NSPs across many conditions and replicates in the same experiment by combining isobaric tandem mass tagging (TMT) with DiDBiT. We applied DiDBiT-TMT to brain slices to determine changes in the de novo proteome that occur after inducing chemical long-term potentiation (cLTP) or treatment with the neuromodulator norepinephrine. We successfully demonstrated DiDBiT-TMT's capacity to quantitatively compare up to 9 samples in parallel. We showed that there is a minimal overlap among NSPs that are differentially expressed in cLTP-treated organotypic brain slices, norepinephrine-treated organotypic brain slices, and organotypic slices undergoing combinatorial treatment with norepinephrine and cLTP. Our results point to the possible divergence of the molecular mechanisms underlying these treatments and showcase the applicability of DiDBiT-TMT for studying neurobiology.

Carbamylated sortilin associates with cardiovascular calcification in patients with chronic kidney disease.

Sortilin, an intracellular sorting receptor, has been identified as a cardiovascular risk factor in the general population. Patients with chronic kidney disease (CKD) are highly susceptible to develop cardiovascular complications such as calcification. However, specific CKD-induced posttranslational protein modifications of sortilin and their link to cardiovascular calcification remain unknown. To investigate this, we examined two independent CKD cohorts for carbamylation of circulating sortilin and detected increased carbamylated sortilin lysine residues in the extracellular domain of sortilin with kidney function decline using targeted mass spectrometry. Structure analysis predicted altered ligand binding by carbamylated sortilin, which was verified by binding studies using surface plasmon resonance measurement, showing an increased affinity of interleukin 6 to in vitro carbamylated sortilin. Further, carbamylated sortilin increased vascular calcification in vitro and ex vivo that was accelerated by interleukin 6. Imaging by mass spectrometry of human calcified arteries revealed in situ carbamylated sortilin. In patients with CKD, sortilin carbamylation was associated with coronary artery calcification, independent of age and kidney function. Moreover, patients with carbamylated sortilin displayed significantly faster progression of coronary artery calcification than patients without sortilin carbamylation. Thus, carbamylated sortilin may be a risk factor for cardiovascular calcification and may contribute to elevated cardiovascular complications in patients with CKD.

Prions amplify through degradation of the VPS10P sorting receptor sortilin.

Prion diseases are a group of fatal neurodegenerative disorders caused by prions, which consist mainly of the abnormally folded isoform of prion protein, PrPSc. A pivotal pathogenic event in prion disease is progressive accumulation of prions, or PrPSc, in brains through constitutive conformational conversion of the cellular prion protein, PrPC, into PrPSc. However, the cellular mechanism by which PrPSc is progressively accumulated in prion-infected neurons remains unknown. Here, we show that PrPSc is progressively accumulated in prion-infected cells through degradation of the VPS10P sorting receptor sortilin. We first show that sortilin interacts with PrPC and PrPSc and sorts them to lysosomes for degradation. Consistently, sortilin-knockdown increased PrPSc accumulation in prion-infected cells. In contrast, overexpression of sortilin reduced PrPSc accumulation in prion-infected cells. These results indicate that sortilin negatively regulates PrPSc accumulation in prion-infected cells. The negative role of sortilin in PrPSc accumulation was further confirmed in sortilin-knockout mice infected with prions. The infected mice had accelerated prion disease with early accumulation of PrPSc in their brains. Interestingly, sortilin was reduced in prion-infected cells and mouse brains. Treatment of prion-infected cells with lysosomal inhibitors, but not proteasomal inhibitors, increased the levels of sortilin. Moreover, sortilin was reduced following PrPSc becoming detectable in cells after infection with prions. These results indicate that PrPSc accumulation stimulates sortilin degradation in lysosomes. Taken together, these results show that PrPSc accumulation of itself could impair the sortilin-mediated sorting of PrPC and PrPSc to lysosomes for degradation by stimulating lysosomal degradation of sortilin, eventually leading to progressive accumulation of PrPSc in prion-infected cells.

Transient denervation of viable myocardium after myocardial infarction does not alter arrhythmia susceptibility.

Cardiac sympathetic nerves stimulate heart rate and force of contraction. Myocardial infarction (MI) leads to the loss of sympathetic nerves within the heart, and clinical studies have indicated that sympathetic denervation is a risk factor for arrhythmias and cardiac arrest. Two distinct types of denervation have been identified in the mouse heart after MI caused by ischemia-reperfusion: transient denervation of peri-infarct myocardium and sustained denervation of the infarct. Sustained denervation is linked to increased arrhythmia risk, but it is not known whether acute nerve loss in peri-infarct myocardium also contributes to arrhythmia risk. Peri-infarct sympathetic denervation requires the p75 neurotrophin receptor (p75NTR), but removal of p75NTR alters the pattern of sympathetic innervation in the heart and increases spontaneous arrhythmias. Therefore, we targeted the p75NTR coreceptor sortilin and the p75NTR-induced protease tumor necrosis factor-α-converting enzyme/A disintegrin and metalloproteinase domain 17 (TACE/ADAM17) to selectively block peri-infarct denervation. Sympathetic nerve density was quantified using immunohistochemistry for tyrosine hydroxylase. Genetic deletion of sortilin had no effect on the timing or extent of axon degeneration, but inhibition of TACE/ADAM17 with the protease inhibitor marimastat prevented the loss of axons from viable myocardium. We then asked whether retention of nerves in peri-infarct myocardium had an impact on cardiac electrophysiology 3 days after MI using ex vivo optical mapping of transmembrane potential and intracellular Ca2+. Preventing acute denervation of viable myocardium after MI did not significantly alter cardiac electrophysiology or Ca2+ handling, suggesting that transient denervation at this early time point has minimal impact on arrhythmia risk. NEW & NOTEWORTHY Sympathetic denervation after myocardial infarction is a risk factor for arrhythmias. We asked whether transient loss of nerves in viable myocardium contributed to arrhythmia risk. We found that targeting protease activity could prevent acute peri-infarct denervation but that it did not significantly alter cardiac electrophysiology or Ca2+ handling 3 days after myocardial infarction.

Risk Locus Identification Ties Alcohol Withdrawal Symptoms to SORCS2.

BACKGROUND: Efforts to promote the cessation of harmful alcohol use are hindered by the affective and physiological components of alcohol withdrawal (AW), which can include life-threatening seizures. Although previous studies of AW and relapse have highlighted the detrimental role of stress, little is known about genetic risk factors. METHODS: We conducted a genome-wide association study of AW symptom count in uniformly assessed subjects with histories of serious AW, followed by additional genotyping in independent AW subjects. RESULTS: The top association signal for AW severity was in sortilin family neurotrophin receptor gene SORCS2 on chromosome 4 (European American meta-analysis n = 1,478, p = 4.3 × 10-9 ). There were no genome-wide significant findings in African Americans (n = 1,231). Bioinformatic analyses were conducted using publicly available high-throughput transcriptomic and epigenomic data sets, showing that in humans SORCS2 is most highly expressed in the nervous system. The identified SORCS2 risk haplotype is predicted to disrupt a stress hormone-modulated regulatory element that has tissue-specific activity in human hippocampus. We used human neural lineage cells to demonstrate in vitro a causal relationship between stress hormone levels and SORCS2 expression, and show that SORCS2 levels in culture are increased upon ethanol exposure and withdrawal. CONCLUSIONS: Taken together, these findings indicate that the pathophysiology of withdrawal may involve the effects of stress hormones on neurotrophic factor signaling. Further investigation of these pathways could produce new approaches to managing the aversive consequences of abrupt alcohol cessation.

The sorting receptor SorCS3 is a stronger regulator of glutamate receptor functions compared to GABAergic mechanisms in the hippocampus.

Correct function of glutamate receptors in the postsynaptic density is crucial to synaptic function and plasticity. SorCS3 (sortilin-related receptor CNS expressed 3) is a sorting receptor which previously has been shown to interact with the key postsynaptic proteins; PSD-95 and PICK1. In this study, we employed electrophysiological analyses of acute brain slices combined with immunohistochemistry to define the role of SorCS3 in hippocampal synapses in CA1 and the dentate gyrus. We analyzed a juvenile (P17-21) and a young adult (P55-65) group of animals from a Sorcs3 knockout mouse model. We show that the basal synaptic transmission is severely affected in SorCS3-deficient neurons in CA1, while only slightly reduced in the dentate gyrus. Specifically, input/output curves of CA1 synapses revealed a 20% reduction of fEPSP (field excitatory postsynaptic potential) slopes at the highest stimulation intensity in knockouts of the juvenile group, which developed to a 33% decrease in young adult animals. These impairments may be a result of changes in the postsynaptic AMPA receptors. Interestingly, repetitive afferent stimulation demonstrated that SorCS3-deficient slices respond with an enhanced synaptic facilitation and reduced synaptic depression. These changes also developed with age. A molecular mechanism underlying this relative increase during repetitive stimulations is compatible with enhanced mobility of postsynaptic AMPA receptors resulting in faster exchange of desensitized receptors in the postsynaptic density. The altered response during repetitive stimulation was characteristic for CA1 but not the dentate gyrus. Immunohistochemical analyses of parvalbumin positive neurons combined with paired-pulse tests of network inhibition and patch-clamp recordings only showed minute inhibitory changes in SorCS3-deficient slices. Our results suggest that SorCS3 serves an important role in the postsynaptic protein network, which is more pronounced in CA1 compared to the dentate gyrus. These data support a role for SorCS3 in controlling proper positioning and mobility of glutamate receptors in the postsynaptic density. © 2016 Wiley Periodicals, Inc.

Quantitative modelling of amyloidogenic processing and its influence by SORLA in Alzheimer's disease.

The extent of proteolytic processing of the amyloid precursor protein (APP) into neurotoxic amyloid-ß (Aß) peptides is central to the pathology of Alzheimer's disease (AD). Accordingly, modifiers that increase Aß production rates are risk factors in the sporadic form of AD. In a novel systems biology approach, we combined quantitative biochemical studies with mathematical modelling to establish a kinetic model of amyloidogenic processing, and to evaluate the influence by SORLA/SORL1, an inhibitor of APP processing and important genetic risk factor. Contrary to previous hypotheses, our studies demonstrate that secretases represent allosteric enzymes that require cooperativity by APP oligomerization for efficient processing. Cooperativity enables swift adaptive changes in secretase activity with even small alterations in APP concentration. We also show that SORLA prevents APP oligomerization both in cultured cells and in the brain in vivo, eliminating the preferred form of the substrate and causing secretases to switch to a less efficient non-allosteric mode of action. These data represent the first mathematical description of the contribution of genetic risk factors to AD substantiating the relevance of subtle changes in SORLA levels for amyloidogenic processing as proposed for patients carrying SORL1 risk alleles.

ABSENCE OF A THYROID PHENOTYPE IN SORTILIN-DEFICIENT MICE.

OBJECTIVE: The Vps10p family member sortilin is expressed in thyroid epithelial cells where it contributes to recycling of the thyroid hormone precursor thyroglobulin (Tg), a process that is thought to render hormone release more effective. Here we investigated the functional impact of sortilin in the thyroid gland using sortilin-deficient mice. METHODS: We measured free T4, thyroid-stimulating hormone (TSH) and Tg serum levels and studied thyroid morphology in 14 sortilin-deficient (Sort1)(-/-)and 12 wildtype (WT) mice. RESULTS: Serum free T4 levels did not differ between Sort1(-/-)and WT females but were significantly lower in Sort1(-/-)males compared with WT (P = .0424). Neither serum TSH nor Tg levels differed between Sort1(-/-)and WT mice, regardless of sex. On the same line, no thyroid histology differences were observed. CONCLUSION: Our findings seem to exclude a role of sortilin in thyroid hormone secretion, although it is possible that the absence of sortilin may result in a thyroid phenotype if combined with other molecular defects of thyroid hormone synthesis and secretion or under iodine deficiency.

Sortilin and SorLA display distinct roles in processing and trafficking of amyloid precursor protein.

The development and progression of Alzheimer's disease is linked to excessive production of toxic amyloid-ß peptide, initiated by ß-secretase cleavage of the amyloid precursor protein (APP). In contrast, soluble APPα (sAPPα) generated by the α-secretase is known to stimulate dendritic branching and enhance synaptic function. Regulation of APP processing, and the shift from neurotrophic to neurotoxic APP metabolism remains poorly understood, but the cellular localization of APP and its interaction with various receptors is considered important. We here identify sortilin as a novel APP interaction partner. Like the related APP receptor SorLA, sortilin is highly expressed in the CNS, but whereas SorLA mainly colocalizes with APP in the soma, sortilin interacts with APP in neurites. The presence of sortilin promotes α-secretase cleavage of APP, unlike SorLA, which inhibits the generation of all soluble products. Also, sortilin and SorLA both bind and mediate internalization of sAPP but to different cellular compartments. The interaction involves the 6A domain of APP, present in both neuronal and non-neuronal APP isoforms. This is important as sAPP receptors described so far only bind the non-neuronal isoforms, leaving SorLA and sortilin as the only receptors for sAPP generated by neurons. Together, our findings establish sortilin, as a novel APP interaction partner that influences both production and cellular uptake of sAPP.

The pro-neurotrophin receptor sortilin is a major neuronal apolipoprotein E receptor for catabolism of amyloid-ß peptide in the brain.

Apolipoprotein E (APOE) is the major risk factor for sporadic Alzheimer's disease. Among other functions, APOE is proposed to sequester neurotoxic amyloid-ß (Aß) peptides in the brain, delivering them to cellular catabolism via neuronal APOE receptors. Still, the receptors involved in this process remain controversial. Here, we identified the pro-neurotrophin receptor sortilin as major endocytic pathway for clearance of APOE/Aß complexes in neurons. Sortilin binds APOE with high affinity. Lack of receptor expression in mice results in accumulation of APOE and of Aß in the brain and in aggravated plaque burden. Also, primary neurons lacking sortilin exhibit significantly impaired uptake of APOE/Aß complexes despite proper expression of other APOE receptors. Despite higher than normal brain APOE levels, sortilin-deficient animals display anomalies in brain lipid metabolism (e.g., accumulation of sulfatides) seen in APOE-deficient mice, indicating functional deficiency in cellular APOE uptake pathways. Together, our findings identified sortilin as an essential neuronal pathway for APOE-containing lipoproteins in vivo and suggest an intriguing link between Aß catabolism and pro-neurotrophin signaling converging on this receptor.

Gentamicin binds to the megalin receptor as a competitive inhibitor using the common ligand binding motif of complement type repeats: insight from the nmr structure of the 10th complement type repeat domain alone and in complex with gentamicin.

Gentamicin is an aminoglycoside widely used in treatments of, in particular, enterococcal, mycobacterial, and severe Gram-negative bacterial infections. Large doses of gentamicin cause nephrotoxicity and ototoxicity, entering the cell via the receptor megalin. Until now, no structural information has been available to describe the interaction with gentamicin in atomic detail, and neither have any three-dimensional structures of domains from the human megalin receptor been solved. To address this gap in our knowledge, we have solved the NMR structure of the 10th complement type repeat of human megalin and investigated its interaction with gentamicin. Using NMR titration data in HADDOCK, we have generated a three-dimensional model describing the complex between megalin and gentamicin. Gentamicin binds to megalin with low affinity and exploits the common ligand binding motif previously described (Jensen, G. A., Andersen, O. M., Bonvin, A. M., Bjerrum-Bohr, I., Etzerodt, M., Thogersen, H. C., O'Shea, C., Poulsen, F. M., and Kragelund, B. B. (2006) J. Mol. Biol. 362, 700-716) utilizing the indole side chain of Trp-1126 and the negatively charged residues Asp-1129, Asp-1131, and Asp-1133. Binding to megalin is highly similar to gentamicin binding to calreticulin. We discuss the impact of this novel insight for the future structure-based design of gentamicin antagonists.

Cubilin, a high affinity receptor for fibroblast growth factor 8, is required for cell survival in the developing vertebrate head.

Cubilin (Cubn) is a multiligand endocytic receptor critical for the intestinal absorption of vitamin B12 and renal protein reabsorption. During mouse development, Cubn is expressed in both embryonic and extra-embryonic tissues, and Cubn gene inactivation results in early embryo lethality most likely due to the impairment of the function of extra-embryonic Cubn. Here, we focus on the developmental role of Cubn expressed in the embryonic head. We report that Cubn is a novel, interspecies-conserved Fgf receptor. Epiblast-specific inactivation of Cubn in the mouse embryo as well as Cubn silencing in the anterior head of frog or the cephalic neural crest of chick embryos show that Cubn is required during early somite stages to convey survival signals in the developing vertebrate head. Surface plasmon resonance analysis reveals that fibroblast growth factor 8 (Fgf8), a key mediator of cell survival, migration, proliferation, and patterning in the developing head, is a high affinity ligand for Cubn. Cell uptake studies show that binding to Cubn is necessary for the phosphorylation of the Fgf signaling mediators MAPK and Smad1. Although Cubn may not form stable ternary complexes with Fgf receptors (FgfRs), it acts together with and/or is necessary for optimal FgfR activity. We propose that plasma membrane binding of Fgf8, and most likely of the Fgf8 family members Fgf17 and Fgf18, to Cubn improves Fgf ligand endocytosis and availability to FgfRs, thus modulating Fgf signaling activity.

Pro-neurotrophins, sortilin, and nociception.

Nerve growth factor (NGF) signaling is important in the development and functional maintenance of nociceptors, but it also plays a central role in initiating and sustaining heat and mechanical hyperalgesia following inflammation. NGF signaling in pain has traditionally been thought of as primarily engaging the classic high-affinity receptor tyrosine kinase receptor TrkA to initiate sensitization events. However, the discovery that secreted proforms of nerve NGF have biological functions distinct from the processed mature factors raised the possibility that these proneurotrophins (proNTs) may have distinct function in painful conditions. ProNTs engage a novel receptor system that is distinct from that of mature neurotrophins, consisting of sortilin, a type I membrane protein belonging to the VPS10p family, and its co-receptor, the classic low-affinity neurotrophin receptor p75NTR. Here, we review how this new receptor system may itself function with or independently of the classic TrkA system in regulating inflammatory or neuropathic pain.

Loss of BDNF or its receptors in three mouse models has unpredictable consequences for anxiety and fear acquisition.

BDNF-induced signaling is essential for the development of the central nervous system and critical for plasticity in adults. Mature BDNF signals through TrkB, while its precursor proBDNF employs p75(NTR), resulting in activation of signaling cascades with opposite effects on neuronal survival, growth cone decisions, and synaptic plasticity. Accordingly, variations in the genes encoding BDNF and its receptors sometimes have opposing influences in psychiatric disorders, and despite the vast literature, consensus is lacking about the behavioral consequences of disrupting the activity of the BDNF system in mice. To dissect the behavioral traits affected by dysfunctional BDNF/TrkB vs. proBDNF/p75(NTR) activity, we studied Bdnf(+/-), Ntrk2(+/-), and Ngfr(-/-) mice in parallel with respect to exploratory behavior, anxiety, startle, and fear acquisition. Our data reveal that the effect of proBDNF/BDNF and its receptors on behavior is more complex than expected. Strikingly, receptor-deficient mice displayed increased risk-taking behavior in the open field and elevated plus maze, whereas lack of proBDNF/BDNF had the opposite effect on mouse behavior. On the other hand, although TrkB signaling is instrumental for acquisition of fear memory in an inhibitory avoidance experiment, lack of p75(NTR) or proBDNF/BDNF conferred increased memory in this task. Importantly, none of the genotypes displayed any deficits in startle reflex, indicating unimpaired response to shock. The combined data illustrate an apparent paradox in the role of the BDNF system in controlling complex behavior and suggest that the individual components may also engage independently in separate signaling pathways.

The loop diuretic bumetanide blocks posttraumatic p75NTR upregulation and rescues injured neurons.

Injured neurons become dependent on trophic factors for survival. However, application of trophic factors to the site of injury is technically extremely challenging. Novel approaches are needed to circumvent this problem. Here, we unravel the mechanism of the emergence of dependency of injured neurons on brain-derived neurotrophic factor (BDNF) for survival. Based on this mechanism, we propose the use of the diuretic bumetanide to prevent the requirement for BDNF and consequent neuronal death in the injured areas. Responses to the neurotransmitter GABA change from hyperpolarizing in intact neurons to depolarizing in injured neurons. We show in vivo in rats and ex vivo in mouse organotypic slice cultures that posttraumatic GABA(A)-mediated depolarization is a cause for the well known phenomenon of pathological upregulation of pan-neurotrophin receptor p75(NTR). The increase in intracellular Ca(2+) triggered by GABA-mediated depolarization activates ROCK (Rho kinase), which in turn leads to the upregulation of p75(NTR). We further show that high levels of p75(NTR) and its interaction with sortilin and proNGF set the dependency on BDNF for survival. Thus, application of bumetanide prevents p75(NTR) upregulation and neuronal death in the injured areas with reduced levels of endogenous BDNF.

Retromer binds the FANSHY sorting motif in SorLA to regulate amyloid precursor protein sorting and processing.

sorLA is a sorting receptor for amyloid precursor protein (APP) genetically linked to Alzheimer's disease (AD). Retromer, an adaptor complex in the endosome-to-Golgi retrieval pathway, has been implicated in APP transport because retromer deficiency leads to aberrant APP sorting and processing and levels of retromer proteins are altered in AD. Here we report that sorLA and retromer functionally interact in neurons to control trafficking and amyloidogenic processing of APP. We have identified a sequence (FANSHY) in the cytoplasmic domain of sorLA that is recognized by the VPS26 subunit of the retromer complex. Accordingly, we characterized the interaction between the retromer complex and sorLA and determined the role of retromer on sorLA-dependent sorting and processing of APP. Mutations in the VPS26 binding site resulted in receptor redistribution to the endosomal network, similar to the situation seen in cells with VPS26 knockdown. The sorLA mutant retained APP-binding activity but, as opposed to the wild-type receptor, misdirected APP into a distinct non-Golgi compartment, resulting in increased amyloid processing. In conclusion, our data provide a molecular link between reduced retromer expression and increased amyloidogenesis as seen in patients with sporadic AD.

Mapping of the interaction site between sortilin and the p75 neurotrophin receptor reveals a regulatory role for the sortilin intracellular domain in p75 neurotrophin receptor shedding and apoptosis.

Neurotrophins comprise a group of neuronal growth factors that are essential for the development and maintenance of the nervous system. However, the immature pro-neurotrophins promote apoptosis by engaging in a complex with sortilin and the p75 neurotrophin receptor (p75(NTR)). To identify the interaction site between sortilin and p75(NTR), we analyzed binding between chimeric receptor constructs and truncated p75(NTR) variants by co-immunoprecipitation experiments, surface plasmon resonance analysis, and FRET. We found that complex formation between sortilin and p75(NTR) relies on contact points in the extracellular domains of the receptors. We also determined that the interaction critically depends on an extracellular juxtamembrane 23-amino acid sequence of p75(NTR). Functional studies further revealed an important regulatory function of the sortilin intracellular domain in p75(NTR)-regulated intramembrane proteolysis and apoptosis. Thus, although the intracellular domain of sortilin does not contribute to p75(NTR) binding, it does regulate the rates of p75(NTR) cleavage, which is required to mediate pro-neurotrophin-stimulated cell death.

SorLA regulates the activity of lipoprotein lipase by intracellular trafficking.

Many different tissues and cell types exhibit regulated secretion of lipoprotein lipase (LPL). However, the sorting of LPL in the trans Golgi network has not, hitherto, been understood in detail. Here, we characterize the role of SorLA (officially known as SorLA-1 or sortilin-related receptor) in the intracellular trafficking of LPL. We found that LPL bound to SorLA under neutral and acidic conditions, and in cells this binding mainly occurred in vesicular structures. SorLA expression changed the subcellular distribution of LPL so it became more concentrated in endosomes. From the endosomes, LPL was further routed to the lysosomes, which resulted in a degradation of newly synthesized LPL. Consequently, an 80% reduction of LPL activity was observed in cells that expressed SorLA. By analogy, SorLA regulated the vesicle-like localization of LPL in primary neuronal cells. Thus, LPL binds to SorLA in the biosynthetic pathway and is subsequently transported to endosomes. As a result of this SorLA mediated-transport, newly synthesized LPL can be routed into specialized vesicles and eventually sent to degradation, and its activity thereby regulated.

Dissecting the role of sortilin receptor signaling in neurodegeneration induced by NGF deprivation.

Sortilin is a member of the family of vacuolar protein sorting 10 protein domain receptors which has emerged as a co-receptor in cell death and neurodegeneration processes mediated by proneurotrophins. Here we tested the possibility that sortilin deficiency interferes with behavioral and neuropathological endpoints in a chronic Nerve Growth factor (NGF)-deprivation model of Alzheimer's disease (AD), the AD10 anti-NGF mouse. AD10 mice show cholinergic deficit, increased APP processing and tau hyper-phosphorylation, resulting in behavioral deficits in learning and memory paradigms assessed by novel object recognition and Morris water maze tests. Sort1(-/-) mice were crossed with AD10 anti-NGF mice and the neurodegenerative phenotype was studied. We found that the loss of sortilin partially protected AD10 anti-NGF mice from neurodegeneration. A protective effect was observed on non-spatial memory as assessed by novel object recognition, and histopathologically at the level of Aß and BFCNs, while the phosphotau increase was unaltered by knocking out sortilin. We suggest that sortilin might be involved in different aspects of neurodegeneration in a complex way, supporting the view that sortilin functions in the CNS are broader than being a co-receptor in proneurotrophin and neurotrophin signaling.

VPS10P-domain receptors - regulators of neuronal viability and function.

VPS10P-domain receptors, such as SORLA and sortilin, constitute a recently identified class of type-1 receptors that are expressed in neurons. Family members are multifunctional proteins that target a range of ligands, including trophic factors and neuropeptides but also other transmembrane proteins. New findings have revealed unexpected roles for VPS10P-domain receptors as regulators of neuronal viability and function through the regulation of both protein transport and signal transduction. Loss of these activities might contribute to the pathophysiology of devastating disorders of the nervous system, including Alzheimer's disease, affective disorders and post-traumatic neuronal cell death.