Prion protein and its ligand stress inducible protein 1 regulate astrocyte development

Comparing Prion Proteins Across Species: Is Zebrafish a Useful Model?

Despite the considerable body of research dedicated to the field of neurodegeneration, the gap in knowledge on the prion protein and its intricate involvement in brain diseases remains substantial. However, in the past decades, many steps forward have been taken toward a better understanding of the molecular mechanisms underlying both the physiological role of the prion protein and the misfolding event converting it into its pathological counterpart, the prion. This review aims to provide an overview of the main findings regarding this protein, highlighting the advantages of many different animal models that share a conserved amino acid sequence and/or structure with the human prion protein. A particular focus will be given to the species Danio rerio, a compelling research organism for the investigation of prion biology, thanks to its conserved orthologs, ease of genetic manipulation, and cost-effectiveness of high-throughput experimentation. We will explore its potential in filling some of the gaps on physiological and pathological aspects of the prion protein, with the aim of directing the future development of therapeutic interventions.

Maternal brain reactive antibodies profile in autism spectrum disorder: an update

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disorder with multifactorial etiologies involving both genetic and environmental factors. In the past two decades it has become clear that in utero exposure to toxins, inflammation, microbiome, and antibodies (Abs), may play a role in the etiology of ASD. Maternal brain-reactive Abs, present in 10-20% of mothers of a child with ASD, pose a potential risk to the developing brain because they can gain access to the brain during gestation, altering brain development during a critical period. Different maternal anti-brain Abs have been associated with ASD and have been suggested to bind extracellular or intracellular neuronal antigens. Clinical data from various cohorts support the increase in prevalence of such maternal brain-reactive Abs in mothers of a child with ASD compared to mothers of a typically developing child. Animal models of both non-human primates and rodents have provided compelling evidence supporting a pathogenic role of these Abs. In this review we summarize the data from clinical and animal models addressing the role of pathogenic maternal Abs in ASD. We propose that maternal brain-reactive Abs are an overlooked and promising field of research, representing a modifiable risk factor that may account for up to 20% of cases of ASD. More studies are needed to better characterize the Abs that contribute to the risk of having a child with ASD, to understand whether we can we predict such cases of ASD, and to better pinpoint the antigenic specificity of these Abs and their mechanisms of pathogenicity.

Hsp70/Hsp90 Organising Protein (Hop): Coordinating Much More than Chaperones

The Hsp70/Hsp90 organising protein (Hop, also known as stress-inducible protein 1/STI1/STIP1) has received considerable attention for diverse cellular functions in both healthy and diseased states. There is extensive evidence that intracellular Hop is a co-chaperone of the major chaperones Hsp70 and Hsp90, playing an important role in the productive folding of Hsp90 client proteins, although recent evidence suggests that eukaryotic Hop is regulatory within chaperone complexes rather than essential. Consequently, Hop is implicated in many key signalling pathways, including aberrant pathways leading to cancer. Hop is also secreted, and it is now well established that Hop interacts with the prion protein, PrP^C, to mediate multiple signalling events. The intracellular and extracellular forms of Hop most likely represent two different isoforms, although the molecular determinants of these divergent functions are yet to be identified. There is also a growing body of research that reports the involvement of Hop in cellular activities that appear independent of either chaperones or PrP^C. While the various cellular functions of Hop have been described, its biological function remains elusive. However, recent knockout studies in mammals suggest that Hop has an important role in embryonic development. This review provides a critical overview of the latest molecular, cellular and biological research on Hop, critically evaluating its function in healthy systems and how this function is adapted in diseased states.

The multiple functions of PrPC in physiological, cancer, and neurodegenerative contexts

Cellular prion protein (PrP^C) is a highly conserved glycoprotein, present both anchored in the cell membrane and soluble in the extracellular medium. It has a diversity of ligands and is variably expressed in numerous tissues and cell subtypes, most notably in the central nervous system (CNS). Its importance has been brought to light over the years both under physiological conditions, such as embryogenesis and immune system homeostasis, and in pathologies, such as cancer and neurodegenerative diseases. During development, PrP^C plays an important role in CNS, participating in axonal growth and guidance and differentiation of glial cells, but also in other organs such as the heart, lung, and digestive system. In diseases, PrP^C has been related to several types of tumors, modulating cancer stem cells, enhancing malignant properties, and inducing drug resistance. Also, in non-neoplastic diseases, such as Alzheimer's and Parkinson's diseases, PrP^C seems to alter the dynamics of neurotoxic aggregate formation and, consequently, the progression of the disease. In this review, we explore in detail the multiple functions of this protein, which proved to be relevant for understanding the dynamics of organism homeostasis, as well as a promising target in the treatment of both neoplastic and degenerative diseases.

The prion protein and its ligands: Insights into structure-function relationships

The prion protein is a multifunctional protein that exists in at least two different folding states. It is subject to diverse proteolytic processing steps that lead to prion protein fragments some of which are membrane-bound whereas others are soluble. A multitude of ligands bind to the prion protein and besides proteinaceous binding partners, interaction with metal ions and nucleic acids occurs. Although of great importance, information on structural and functional consequences of prion protein binding to its partners is limited. Here, we will reflect on the structure-function relationship of the prion protein and its binding partners considering the different folding states and prion protein fragments.

With or without You: Co-Chaperones Mediate Health and Disease by Modifying Chaperone Function and Protein Triage

Heat shock proteins (HSPs) are a family of molecular chaperones that regulate essential protein refolding and triage decisions to maintain protein homeostasis. Numerous co-chaperone proteins directly interact and modify the function of HSPs, and these interactions impact the outcome of protein triage, impacting everything from structural proteins to cell signaling mediators. The chaperone/co-chaperone machinery protects against various stressors to ensure cellular function in the face of stress. However, coding mutations, expression changes, and post-translational modifications of the chaperone/co-chaperone machinery can alter the cellular stress response. Importantly, these dysfunctions appear to contribute to numerous human diseases. Therapeutic targeting of chaperones is an attractive but challenging approach due to the vast functions of HSPs, likely contributing to the off-target effects of these therapies. Current efforts focus on targeting co-chaperones to develop precise treatments for numerous diseases caused by defects in protein quality control. This review focuses on the recent developments regarding selected HSP70/HSP90 co-chaperones, with a concentration on cardioprotection, neuroprotection, cancer, and autoimmune diseases. We also discuss therapeutic approaches that highlight both the utility and challenges of targeting co-chaperones.

Prions and prion diseases: Insights from the eye

Prion diseases are invariably fatal neurodegenerative disorders that have gained much publicity due to their transmissible nature. Sporadic Creutzfeldt-Jakob disease (sCJD) is the most common human prion disorder, with an incidence of 1 in a million. Inherited prion disorders are relatively rare, and associated with mutations in the prion protein gene. More than 50 different point mutations, deletions, and insertions have been identified so far. Most are autosomal dominant and fully penetrant. Prion disorders also occur in animals, and are of major concern because of the potential for spreading to humans. The principal pathogenic event underlying all prion disorders is a change in the conformation of prion protein (PrP^C) from a mainly α-helical to a β-sheet rich isoform, PrP-scrapie (PrP^Sc). Accumulation of PrP^Sc in the brain parenchyma is the major cause of neuronal degeneration. The mechanism by which PrP^Sc is transmitted, propagates, and causes neurodegenerative changes has been investigated over the years, and several clues have emerged. Efforts are also ongoing for identifying specific and sensitive diagnostic tests for sCJD and animal prion disorders, but success has been limited. The eye is suitable for these evaluations because it shares several anatomical and physiological features with the brain, and can be observed in vivo during disease progression. The retina, considered an extension of the central nervous system, is involved extensively in prion disorders. Accordingly, Optical Coherence Tomography and electroretinogram have shown some promise as pre-mortem diagnostic tests for human and animal prion disorders. However, a complete understanding of the physiology of PrP^C and pathobiology of PrP^Sc in the eye is essential for developing specific and sensitive tests. Below, we summarize recent progress in ocular physiology and pathology in prion disorders, and the eye as an anatomically accessible site to diagnose, monitor disease progression, and test therapeutic options.

The multiple functions of the co-chaperone stress inducible protein 1

Stress inducible protein 1 (STI1) is a co-chaperone acting with Hsp70 and Hsp90 for the correct client proteins' folding and therefore for the maintenance of cellular homeostasis. Besides being expressed in the cytosol, STI1 can also be found both in the cell membrane and the extracellular medium playing several relevant roles in the central nervous system (CNS) and tumor microenvironment. During CNS development, in association with cellular prion protein (PrP^c), STI1 regulates crucial events such as neuroprotection, neuritogenesis, astrocyte differentiation and survival. In cancer, STI1 is involved with tumor growth and invasion, is undoubtedly a pro-tumor factor, being considered as a biomarker and possibly therapeutic target for several malignancies. In this review, we discuss current knowledge and new findings on STI1 function as well as its role in tissue homeostasis, CNS and tumor progression.

Sleep deprivation regulates availability of PrPC and Aβ peptides which can impair interaction between PrPC and laminin and neuronal plasticity

PrP^C is a glycoprotein capable to interact with several molecules and mediates diverse signaling pathways. Among numerous ligands, laminin (LN) is known to promote neurite outgrowth and memory consolidation, while amyloid‐beta oligomers (Aβo) trigger synaptic dysfunction. In both pathways, mGluR1 is recruited as co‐receptor. The involvement of PrP^C/mGluR1 in these opposite functions suggests that this complex is a key element in the regulation of synaptic activity. Considering that sleep‐wake cycle is important for synaptic homeostasis, we aimed to investigate how sleep deprivation affects the expression of PrP^C and its ligands, laminin, Aβo, and mGluR1, a multicomplex that can interfere with neuronal plasticity. To address this question, hippocampi of control (CT) and sleep deprived (SD) C57BL/6 mice were collected at two time points of circadian period (13 hr and 21 hr). We observed that sleep deprivation reduced PrP^C and mGluR1 levels with higher effect in active state (21 hr). Sleep deprivation also caused accumulation of Aβ peptides in rest period (13 hr), while laminin levels were not affected. In vitro binding assay showed that Aβo can compete with LN for PrP^C binding. The influence of Aβo was also observed in neuritogenesis. LN alone promoted longer neurite outgrowth than non‐treated cells in both Prnp^+/+ and Prnp^0/0 genotypes. Aβo alone did not show any effects, but when added together with LN, it attenuated the effects of LN only in Prnp^+/+ cells. Altogether, our findings indicate that sleep deprivation regulates the availability of PrP^C and Aβ peptides, and based on our in vitro assays, these alterations induced by sleep deprivation can negatively affect LN–PrP^C interaction, which is known to play roles in neuronal plasticity.

Prion Protein in Glioblastoma Multiforme

The cellular prion protein (PrPc) is an evolutionarily conserved cell surface protein encoded by the PRNP gene. PrPc is ubiquitously expressed within nearly all mammalian cells, though most abundantly within the CNS. Besides being implicated in the pathogenesis and transmission of prion diseases, recent studies have demonstrated that PrPc contributes to tumorigenesis by regulating tumor growth, differentiation, and resistance to conventional therapies. In particular, PrPc over-expression has been related to the acquisition of a malignant phenotype of cancer stem cells (CSCs) in a variety of solid tumors, encompassing pancreatic ductal adenocarcinoma (PDAC), osteosarcoma, breast cancer, gastric cancer, and primary brain tumors, mostly glioblastoma multiforme (GBM). Thus, PrPc is emerging as a key in maintaining glioblastoma cancer stem cells’ (GSCs) phenotype, thereby strongly affecting GBM infiltration and relapse. In fact, PrPc contributes to GSCs niche’s maintenance by modulating GSCs’ stem cell-like properties while restraining them from differentiation. This is the first review that discusses the role of PrPc in GBM. The manuscript focuses on how PrPc may act on GSCs to modify their expression and translational profile while making the micro-environment surrounding the GSCs niche more favorable to GBM growth and infiltration.

Hsp90 and Its Co-Chaperones in Neurodegenerative Diseases

Proper folding is crucial for proteins to achieve functional activity in the cell. However, it often occurs that proteins are improperly folded (misfolded) and form aggregates, which are the main hallmark of many diseases including cancers, neurodegenerative diseases and many others. Proteins that assist other proteins in proper folding into three-dimensional structures are chaperones and co-chaperones. The key role of chaperones/co-chaperones is to prevent protein aggregation, especially under stress. An imbalance between chaperone/co-chaperone levels has been documented in neurons, and suggested to contribute to protein misfolding. An essential protein and a major regulator of protein folding in all eukaryotic cells is the heat shock protein 90 (Hsp90). The function of Hsp90 is tightly regulated by many factors, including co-chaperones. In this review we summarize results regarding the role of Hsp90 and its co-chaperones in neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and prionopathies.

Role of FOXC1 in regulating APSCs self-renewal via STI-1/PrPC signaling

Forkhead box protein C1 (FOXC1) is known to regulate developmental processes in the skull and brain. Methods: The unique multipotent arachnoid-pia stem cells (APSCs) isolated from human and mouse arachnoid-pia membranes of meninges were grown as 3D spheres and displayed a capacity for self-renewal. Additionally, APSCs also expressed the surface antigens as mesenchymal stem cells. By applying the FOXC1 knockout mice and mouse brain explants, signaling cascade of FOXC1-STI-1-PrP^C was investigated to demonstrate the molecular regulatory pathway for APSCs self-renewal. Moreover, APSCs implantation in stroke model was also verified whether neurogenic property of APSCs could repair the ischemic insult of the stroke brain. Results: Activated FOXC1 regulated the proliferation of APSCs in a cell cycle-dependent manner, whereas FOXC1-mediated APSCs self-renewal was abolished in FOXC1 knockout mice (FOXC1^-/- mice). Moreover, upregulation of STI-1 regulated by FOXC1 enhanced cell survival and self-renewal of APSCs through autocrine signaling of cellular prion protein (PrP^C). Mouse brain explants STI-1 rescues the cortical phenotype in vitro and induces neurogenesis in the FOXC1 ^-/- mouse brain. Furthermore, administration of APSCs in ischemic brain restored the neuroglial microenvironment and improved neurological dysfunction. Conclusion: We identified a novel role for FOXC1 in the direct regulation of the STI-1-PrP^C signaling pathway to promote cell proliferation and self-renewal of APSCs.

Down-regulation of STIP1 regulate apoptosis and invasion of glioma cells via TRAP1/AKT signaling pathway

BACKGROUND

In recent years, many studies have confirmed that STIP1 (phosphorylation-induced protein 1) is involved in the development and progression of various tumors. However, its potential role in glioma progression and the underlying mechanisms of glioma development remain unclear.

METHODS

We analyzed the expression of STIP1 in 35 human glioma tissue specimens of different grades, using 6 normal brain tissues for comparison. We transfected U87 and U251 cell lines with small interfering RNA (siRNA) to downregulate STIP1, and set up a negative control group and a blank group for comparison. The MTT assay was used to detect cell proliferation, and cell cycle progression and apoptosis were analyzed through flow cytometry. Transwell experiments were employed to detect the invasion and migration of STIP1-depleted and control U87 and U251 cells and western blotting was used to detect the expression of TRAP1/Akt pathway proteins. In addition, immunohistochemical analysis was used to reveal differences in expression and localization between transplanted tumor specimens of each group.

RESULTS

We observed a high expression of STIP1 in glioblastoma, MTT assay revealed a decreased cell proliferation rate in the STIP1-downregulated cells. Cell cycle analysis revealed an increased proportion of cells in G1 phase, as well as an increase in apoptosis, upon STIP1 downregulation. Western blotting showed that TRAP1, pAkt, and MMP2 expression was decreased upon STIP1 downregulation. In addition, TRAP1, ki-67, and MMP2 displayed a decreased expression in vivo.

CONCLUSIONS

STIP1 is highly expressed in glioblastoma compared to normal brain tissues. Downregulation of STIP1 in glioma cells reduces cell proliferation rate and invasion and increases cell apoptosis.

The prion protein in neuroimmune crosstalk

The cellular prion protein (PrP^C) is a medium-sized glycoprotein, attached to the cell surface by a glycosylphosphatidylinositol anchor. PrP^C is encoded by a single-copy gene, PRNP, which is abundantly expressed in the central nervous system and at lower levels in non-neuronal cells, including those of the immune system. Evidence from experimental knockout of PRNP in rodents, goats, and cattle and the occurrence of a nonsense mutation in goat that prevents synthesis of PrP^C, have shown that the molecule is non-essential for life. Indeed, no easily recognizable phenotypes are associate with a lack of PrP^C, except the potentially advantageous trait that animals without PrP^C cannot develop prion disease. This is because, in prion diseases, PrP^C converts to a pathogenic "scrapie" conformer, PrP^Sc, which aggregates and eventually induces neurodegeneration. In addition, endogenous neuronal PrP^C serves as a toxic receptor to mediate prion-induced neurotoxicity. Thus, PrP^C is an interesting target for treatment of prion diseases. Although loss of PrP^C has no discernable effect, alteration of its normal physiological function can have very harmful consequences. It is therefore important to understand cellular processes involving PrP^C, and research of this topic has advanced considerably in the past decade. Here, we summarize data that indicate the role of PrP^C in modulating immune signaling, with emphasis on neuroimmune crosstalk both under basal conditions and during inflammatory stress.

IL-7-induced phosphorylation of the adaptor Crk-like and other targets

IL-7 is required for T cell differentiation and mature T cell homeostasis and promotes pro-B cell proliferation and survival. Tyrosine phosphorylation plays a central role in IL-7 signaling. We identified by two-dimensional electrophoresis followed by anti-phosphotyrosine immunoblotting and mass spectrometry sixteen tyrosine phosphorylated proteins from the IL-7-dependent cell line D1. IL-7 stimulation induced the phosphorylation of the proteins STI1, ATIC and hnRNPH, involved in pathways related to survival, proliferation and gene expression, respectively, and increased the phosphorylation of CrkL, a member of a family of adaptors including the highly homologous Crk isoforms CrkII and CrkI, important in multiple signaling pathways. We observed an increased phosphorylation of CrkL in murine pro-B cells and in murine and human T cells. In addition, IL-7 increased the association of CrkL with the transcription factor Stat5, essential for IL-7 pro-survival activity. The selective tyrosine kinase inhibitor Imatinib. counteracted the IL-7 pro-survival effect in D1 cells and decreased CrkL phosphorylation. These data suggested that CrkL could play a pro-survival role in IL-7-mediated signaling. We observed that pro-B cells also expressed, in addition to CrkL, the Crk isoforms CrkII and CrkI and therefore utilized pro-B cells conditionally deficient in all three to evaluate the role of these proteins. The observation that the IL-7 pro-survival effect was reduced in Crk/CrkL conditionally-deficient pro-B cells further pointed to a pro-survival role of these adaptors. To further evaluate the role of these proteins, gene expression studies were performed in Crk/CrkL conditionally-deficient pro-B cells. IL-7 decreased the transcription of the receptor LAIR1, which inhibits B cell proliferation, in a Crk/CrkL-dependent manner, suggesting that the Crk family of proteins may promote pro-B cell proliferation. Our data contribute to the understanding of IL-7 signaling and suggest the involvement of Crk family proteins in pathways promoting survival and proliferation.

Involvement of STI1 protein in the differentiation process of Trypanosoma cruzi

The protozoan Trypanosoma cruzi is a parasite exposed to several environmental stressors inside its invertebrate and vertebrate hosts. Although stress conditions are involved in its differentiation processes, little information is available about the stress response proteins engaged in these activities. This work reports the first known association of the stress-inducible protein 1 (STI1) with the cellular differentiation process in a unicellular eukaryote. Albeit STI1 expression is constitutive in epimastigotes and metacyclic trypomastigotes, higher protein levels were observed in late growth phase epimastigotes subjected to nutritional stress. Analysis by indirect immunofluorescence revealed that T. cruzi STI1 (TcSTI1) is located throughout the cell cytoplasm, with some cytoplasmic granules appearing in greater numbers in late growing epimastigotes and late growing epimastigotes subjected to nutritional stress. We observed that part of the fluorescence signal from both TcSTI1 and TcHSP70 colocalized around the nucleus. Gene silencing of sti1 in Trypanosoma brucei did not affect cell growth. Similarly, the growth of T. cruzi mutant parasites with a single allele sti1 gene knockout was not affected. However, the differentiation of epimastigotes in metacyclic trypomastigotes (metacyclogenesis) was compromised. Lower production rates and numbers of metacyclic trypomastigotes were obtained from the mutant parasites compared with the wild-type parasites. These data indicate that reduced levels of TcSTI1 decrease the rate of in vitro metacyclogenesis, suggesting that this protein may participate in the differentiation process of T. cruzi.

Maternal autoimmune antibodies alter the dendritic arbor and spine numbers in the infragranular layers of the cortex

An association between maternal IgG antibodies reactive against proteins in fetal brain and an outcome of autism in the child has been identified. Using a mouse model of prenatal intraventricular administration of autism-specific maternal IgG, we demonstrated that these antibodies produce behavioral alterations similar to those in children with ASD. We previously demonstrated that these antibodies bind to radial glial stem cells (RG) and observed an increase in the number of divisions of translocating RG in the developing cortex. We also showed an alteration in brain size and as well as a generalized increased of neuronal volume in adult mice. Here, we used our intraventricular mouse model of antibody administration, followed by Golgi and Neurolucida analysis to demonstrate that during midstages of neurogenesis these maternal autism-specific antibodies produced a consistent decrease in the number of spines in the infragranular layers in the adult cortical areas analyzed. Specifically, in the frontal cortex basal dendrites of layer V neurons were decreased in length and volume, and both the total number of spines-mature and immature-and the spine density were lower than in the control neurons from the same region. Further, in the occipital cortex layer VI neurons presented with a decrease in the total number of spines and in the spine density in the apical dendrite, as well as decrease in the number of mature spines in the apical and basal dendrites. Interestingly, the time of exposure to these antibodies (E14.5) coincides with the generation of pyramidal neurons in layer V in the frontal cortex and in layer VI in the occipital cortex, following the normal rostro-caudal pattern of cortical cell generation. We recently demonstrated that one of the primary antigens recognized by these antibodies corresponds to stress-induced phosphoprotein 1 (STIP1). Here we hypothesize that the reduction in the access of newborn cells to STIP1 in the developing cortex may be responsible for the reduced dendritic arborization and number of spines we noted in the adult cortex.

Evidence of a Cell Surface Role for Hsp90 Complex Proteins Mediating Neuroblast Migration in the Subventricular Zone

In most mammalian brains, the subventricular zone (SVZ) is a germinative layer that maintains neurogenic activity throughout adulthood. Neuronal precursors arising from this region migrate through the rostral migratory stream (RMS) and reach the olfactory bulbs where they differentiate and integrate into the local circuitry. Recently, studies have shown that heat shock proteins have an important role in cancer cell migration and blocking Hsp90 function was shown to hinder cell migration in the developing cerebellum. In this work, we hypothesize that chaperone complexes may have an important function regulating migration of neuronal precursors from the subventricular zone. Proteins from the Hsp90 complex are present in the postnatal SVZ as well as in the RMS. Using an in vitro SVZ explant model, we have demonstrated the expression of Hsp90 and Hop/STI1 by migrating neuroblasts. Treatment with antibodies against Hsp90 and co-chaperone Hop/STI1, as well as Hsp90 and Hsp70 inhibitors hinder neuroblast chain migration. Time-lapse videomicroscopy analysis revealed that cell motility and average migratory speed was decreased after exposure to both antibodies and inhibitors. Antibodies recognizing Hsp90, Hsp70, and Hop/STI1 were found bound to the membranes of cells from primary SVZ cultures and biotinylation assays demonstrated that Hsp70 and Hop/STI1 could be found on the external leaflet of neuroblast membranes. The latter could also be detected in conditioned medium samples obtained from cultivated SVZ cells. Our results suggest that chaperones Hsp90, Hsp70, and co-chaperone Hop/STI1, components of the Hsp90 complex, regulate SVZ neuroblast migration in a concerted manner through an extracellular mechanism.

The Hsp70/Hsp90 Chaperone Machinery in Neurodegenerative Diseases

The accumulation of misfolded proteins in the human brain is one of the critical features of many neurodegenerative diseases, including Alzheimer's disease (AD). Assembles of beta-amyloid (Aβ) peptide—either soluble (oligomers) or insoluble (plaques) and of tau protein, which form neurofibrillary tangles, are the major hallmarks of AD. Chaperones and co-chaperones regulate protein folding and client maturation, but they also target misfolded or aggregated proteins for refolding or for degradation, mostly by the proteasome. They form an important line of defense against misfolded proteins and are part of the cellular quality control system. The heat shock protein (Hsp) family, particularly Hsp70 and Hsp90, plays a major part in this process and it is well-known to regulate protein misfolding in a variety of diseases, including tau levels and toxicity in AD. However, the role of Hsp90 in regulating protein misfolding is not yet fully understood. For example, knockdown of Hsp90 and its co-chaperones in a Caenorhabditis elegans model of Aβ misfolding leads to increased toxicity. On the other hand, the use of Hsp90 inhibitors in AD mouse models reduces Aβ toxicity, and normalizes synaptic function. Stress-inducible phosphoprotein 1 (STI1), an intracellular co-chaperone, mediates the transfer of clients from Hsp70 to Hsp90. Importantly, STI1 has been shown to regulate aggregation of amyloid-like proteins in yeast. In addition to its intracellular function, STI1 can be secreted by diverse cell types, including astrocytes and microglia and function as a neurotrophic ligand by triggering signaling via the cellular prion protein (PrP^C). Extracellular STI1 can prevent Aβ toxic signaling by (i) interfering with Aβ binding to PrP^C and (ii) triggering pro-survival signaling cascades. Interestingly, decreased levels of STI1 in C. elegans can also increase toxicity in an amyloid model. In this review, we will discuss the role of intracellular and extracellular STI1 and the Hsp70/Hsp90 chaperone network in mechanisms underlying protein misfolding in neurodegenerative diseases, with particular focus on AD.

The biological function of the cellular prion protein: an update

The misfolding of the cellular prion protein (PrP^C) causes fatal neurodegenerative diseases. Yet PrP^C is highly conserved in mammals, suggesting that it exerts beneficial functions preventing its evolutionary elimination. Ablation of PrP^C in mice results in well-defined structural and functional alterations in the peripheral nervous system. Many additional phenotypes were ascribed to the lack of PrP^C, but some of these were found to arise from genetic artifacts of the underlying mouse models. Here, we revisit the proposed physiological roles of PrP^C in the central and peripheral nervous systems and highlight the need for their critical reassessment using new, rigorously controlled animal models.

PRNP/prion protein regulates the secretion of exosomes modulating CAV1/caveolin-1-suppressed autophagy

Prion protein modulates many cellular functions including the secretion of trophic factors by astrocytes. Some of these factors are found in exosomes, which are formed within multivesicular bodies (MVBs) and secreted into the extracellular space to modulate cell-cell communication. The mechanisms underlying exosome biogenesis were not completely deciphered. Here, we demonstrate that primary cultures of astrocytes and fibroblasts from prnp-null mice secreted lower levels of exosomes than wild-type cells. Furthermore, prnp-null astrocytes exhibited reduced MVB formation and increased autophagosome formation. The reconstitution of PRNP expression at the cell membrane restored exosome secretion in PRNP-deficient astrocytes, whereas macroautophagy/autophagy inhibition via BECN1 depletion reestablished exosome release in these cells. Moreover, the PRNP octapeptide repeat domain was necessary to promote exosome secretion and to impair the formation of the CAV1-dependent ATG12-ATG5 cytoplasmic complex that drives autophagosome formation. Accordingly, higher levels of CAV1 were found in lipid raft domains instead of in the cytoplasm in prnp-null cells. Collectively, these findings demonstrate that PRNP supports CAV1-suppressed autophagy to protect MVBs from sequestration into phagophores, thus facilitating exosome secretion.

Almost a century of prion protein(s): From pathology to physiology, and back to pathology

Prions are one of the few pathogens whose name is renowned at all population levels, after the dramatic years pervaded by the fear of eating prion-infected food. If now this, somehow irrational, scare of bovine meat inexorably transmitting devastating brain disorders is largely subdued, several prion-related issues are still unsolved, precluding the design of therapeutic approaches that could slow, if not halt, prion diseases. One unsolved issue is, for example, the role of the prion protein (PrP^C), whole conformational misfolding originates the prion but whose physiologic reason d'etre in neurons, and in cells at large, remains enigmatic. Preceded by a historical outline, the present review will discuss the functional pleiotropicity ascribed to PrP^C, and whether this aspect could fall, at least in part, into a more concise framework. It will also be devoted to radically different perspectives for PrP^C, which have been recently brought to the attention of the scientific world with unexpected force. Finally, it will discuss the possible reasons allowing an evolutionary conserved and benign protein, as PrP^C is, to turn into a high affinity receptor for pathologic misfolded oligomers, and to transmit their toxic message into neurons.

Prion protein binding to HOP modulates the migration and invasion of colorectal cancer cells

Colorectal cancer (CRC) is one of the most frequently diagnosed malignancies. The generation of conventional treatments has improved, but approximately 50 % of patients with CRC who undergo potentially curative surgery ultimately relapse and die, usually as a consequence of metastatic disease. Our previous findings showed that engagement of the cellular prion protein (PrP(C)) to its ligand HSP70/90 heat shock organizing protein (HOP) induces proliferation of glioblastomas. In addition, PrP(C) has been described as an important modulator of colorectal tumor growth. Here, we investigated the biological relevance of the PrP(C)-HOP interaction in CRC cells. We demonstrate that HOP induced the migration and invasion of CRC cell lines in a PrP(C)-dependent manner and that phosphorylation of the ERK1/2 pathway is a downstream mediator of these effects. Additionally, we show that a HOP peptide with the ability to bind PrP(C) and abolish the PrP(C)-HOP interaction inhibited the migration and invasion of CRC cells. Together, these data indicate that the disruption of the PrP(C)-HOP complex could be a potential therapeutic target for modulating the migratory and invasive cellular properties that lead to metastatic CRC.

The Cellular Prion Protein: A Player in Immunological Quiescence

Despite intensive studies since the 1990s, the physiological role of the cellular prion protein (PrP(C)) remains elusive. Here, we present a novel concept suggesting that PrP(C) contributes to immunological quiescence in addition to cell protection. PrP(C) is highly expressed in diverse organs that by multiple means are particularly protected from inflammation, such as the brain, eye, placenta, pregnant uterus, and testes, while at the same time it is expressed in most cells of the lymphoreticular system. In this paradigm, PrP(C) serves two principal roles: to modulate the inflammatory potential of immune cells and to protect vulnerable parenchymal cells against noxious insults generated through inflammation. Here, we review studies of PrP(C) physiology in view of this concept.

Domain-Specific Activation of Death-Associated Intracellular Signalling Cascades by the Cellular Prion Protein in Neuroblastoma Cells

The biological functions of the cellular prion protein remain poorly understood. In fact, numerous studies have aimed to determine specific functions for the different protein domains. Studies of cellular prion protein (PrP(C)) domains through in vivo expression of molecules carrying internal deletions in a mouse Prnp null background have provided helpful data on the implication of the protein in signalling cascades in affected neurons. Nevertheless, understanding of the mechanisms underlying the neurotoxicity induced by these PrP(C) deleted forms is far from complete. To better define the neurotoxic or neuroprotective potential of PrP(C) N-terminal domains, and to overcome the heterogeneity of results due to the lack of a standardized model, we used neuroblastoma cells to analyse the effects of overexpressing PrP(C) deleted forms. Results indicate that PrP(C) N-terminal deleted forms were properly processed through the secretory pathway. However, PrPΔF35 and PrPΔCD mutants led to death by different mechanisms sharing loss of alpha-cleavage and activation of caspase-3. Our data suggest that both gain-of-function and loss-of-function pathogenic mechanisms may be associated with N-terminal domains and may therefore contribute to neurotoxicity in prion disease. Dissecting the molecular response induced by PrPΔF35 may be the key to unravelling the physiological and pathological functions of the prion protein.

Hsp70/Hsp90 organising protein (hop): beyond interactions with chaperones and prion proteins

The Hsp70/Hsp90 organising protein (Hop), also known as stress-inducible protein 1 (STI1), has received considerable attention for diverse cellular functions in both healthy and diseased states. There is extensive evidence that intracellular Hop is a co-chaperone of the major chaperones Hsp70 and Hsp90, playing an important role in the productive folding of Hsp90 client proteins. Consequently, Hop is implicated in a number of key signalling pathways, including aberrant pathways leading to cancer. However, Hop is also secreted and it is now well established that Hop also serves as a receptor for the prion protein, PrP(C). The intracellular and extracellular forms of Hop most likely represent two different isoforms, although the molecular determinants of these divergent functions are yet to be identified. There is also a growing body of research that reports the involvement of Hop in cellular activities that appear independent of either chaperones or PrP(C). While Hop has been shown to have various cellular functions, its biological function remains elusive. However, recent knockout studies in mammals suggest that Hop has an important role in embryonic development. This review provides a critical overview of the latest molecular, cellular and biological research on Hop, critically evaluating its function in healthy systems and how this function is adapted in diseases states.

Prenatal Exposure to Autism-Specific Maternal Autoantibodies Alters Proliferation of Cortical Neural Precursor Cells, Enlarges Brain, and Increases Neuronal Size in Adult Animals

Autism spectrum disorders (ASDs) affect up to 1 in 68 children. Autism-specific autoantibodies directed against fetal brain proteins have been found exclusively in a subpopulation of mothers whose children were diagnosed with ASD or maternal autoantibody-related autism. We tested the impact of autoantibodies on brain development in mice by transferring human antigen-specific IgG directly into the cerebral ventricles of embryonic mice during cortical neurogenesis. We show that autoantibodies recognize radial glial cells during development. We also show that prenatal exposure to autism-specific maternal autoantibodies increased stem cell proliferation in the subventricular zone (SVZ) of the embryonic neocortex, increased adult brain size and weight, and increased the size of adult cortical neurons. We propose that prenatal exposure to autism-specific maternal autoantibodies directly affects radial glial cell development and presents a viable pathologic mechanism for the maternal autoantibody-related prenatal ASD risk factor.

Prion Protein Signaling in the Nervous System—A Review and Perspective

Prion protein (PrPC) was originally known as the causative agent of transmissible spongiform encephalopathy (TSE) but with recent research, its true function in cells is becoming clearer. It is known to act as a scaffolding protein, binding multiple ligands at the cell membrane and to be involved in signal transduction, passing information from the extracellular matrix (ECM) to the cytoplasm. Its role in the coordination of transmitters at the synapse, glyapse, and gap junction and in short- and long-range neurotrophic signaling gives PrPC a major part in neural transmission and nervous system signaling. It acts to regulate cellular function in multiple targets through its role as a controller of redox status and calcium ion flux. Given the importance of PrPC in cell physiology, this review considers its potential role in disease apart from TSE. The putative functions of PrPC point to involvement in neurodegenerative disease, neuropathic pain, chronic headache, and inflammatory disease including neuroinflammatory disease of the nervous system. Potential targets for the treatment of disease influenced by PrPC are discussed.

The cellular form of the prion protein guides the differentiation of human embryonic stem cells into neuron-, oligodendrocyte-, and astrocyte-committed lineages

Prion protein, PrP(C), is a glycoprotein that is expressed on the cell surface beginning with the early stages of embryonic stem cell differentiation. Previously, we showed that ectopic expression of PrP(C) in human embryonic stem cells (hESCs) triggered differentiation toward endodermal, mesodermal, and ectodermal lineages, whereas silencing of PrP(C) suppressed differentiation toward ectodermal but not endodermal or mesodermal lineages. Considering that PrP(C) might be involved in controlling the balance between cells of different lineages, the current study was designed to test whether PrP(C) controls differentiation of hESCs into cells of neuron-, oligodendrocyte-, and astrocyte-committed lineages. PrP(C) was silenced in hESCs cultured under three sets of conditions that were previously shown to induce hESCs differentiation into predominantly neuron-, oligodendrocyte-, and astrocyte-committed lineages. We found that silencing of PrP(C) suppressed differentiation toward all three lineages. Similar results were observed in all three protocols, arguing that the effect of PrP(C) was independent of differentiation conditions employed. Moreover, switching PrP(C) expression during a differentiation time course revealed that silencing PrP(C) expression during the very initial stage that corresponds to embryonic bodies has a more significant impact than silencing at later stages of differentiation. The current work illustrates that PrP(C) controls differentiation of hESCs toward neuron-, oligodendrocyte-, and astrocyte-committed lineages and is likely involved at the stage of uncommitted neural progenitor cells rather than lineage-committed neural progenitors.

To develop with or without the prion protein

The deletion of the cellular form of the prion protein (PrP^C) in mouse, goat, and cattle has no drastic phenotypic consequence. This stands in apparent contradiction with PrP^C quasi-ubiquitous expression and conserved primary and tertiary structures in mammals, and its pivotal role in neurodegenerative diseases such as prion and Alzheimer's diseases. In zebrafish embryos, depletion of PrP ortholog leads to a severe loss-of-function phenotype. This raises the question of a potential role of PrP^C in the development of all vertebrates. This view is further supported by the early expression of the PrP^C encoding gene (Prnp) in many tissues of the mouse embryo, the transient disruption of a broad number of cellular pathways in early Prnp^−/− mouse embryos, and a growing body of evidence for PrP^C involvement in the regulation of cell proliferation and differentiation in various types of mammalian stem cells and progenitors. Finally, several studies in both zebrafish embryos and in mammalian cells and tissues in formation support a role for PrP^C in cell adhesion, extra-cellular matrix interactions and cytoskeleton. In this review, we summarize and compare the different models used to decipher PrP^C functions at early developmental stages during embryo- and organo-genesis and discuss their relevance.

PrP(C) from stem cells to cancer

The cellular prion protein PrP(C) was initially discovered as the normal counterpart of the pathological scrapie prion protein PrP(Sc), the main component of the infectious agent of Transmissible Spongiform Encephalopathies. While clues as to the physiological function of this ubiquitous protein were greatly anticipated from the development of knockout animals, PrP-null mice turned out to be viable and to develop without major phenotypic abnormalities. Notwithstanding, the discovery that hematopoietic stem cells from PrP-null mice have impaired long-term repopulating potential has set the stage for investigating into the role of PrP(C) in stem cell biology. A wealth of data have now exemplified that PrP(C) is expressed in distinct types of stem cells and regulates their self-renewal as well as their differentiation potential. A role for PrP(C) in the fate restriction of embryonic stem cells has further been proposed. Paralleling these observations, an overexpression of PrP(C) has been documented in various types of tumors. In line with the contribution of PrP(C) to stemness and to the proliferation of cancer cells, PrP(C) was recently found to be enriched in subpopulations of tumor-initiating cells. In the present review, we summarize the current knowledge of the role played by PrP(C) in stem cell biology and discuss how the subversion of its function may contribute to cancer progression.

Stress protein expression in early phase spinal cord ischemia/reperfusion injury

Spinal cord ischemia/reperfusion injury is a stress injury to the spinal cord. Our previous studies using differential proteomics identified 21 differentially expressed proteins (n > 2) in rabbits with spinal cord ischemia/reperfusion injury. Of these proteins, stress-related proteins included protein disulfide isomerase A3, stress-induced-phosphoprotein 1 and heat shock cognate protein 70. In this study, we established New Zealand rabbit models of spinal cord ischemia/reperfusion injury by abdominal aorta occlusion. Results demonstrated that hind limb function initially improved after spinal cord ischemia/reperfusion injury, but then deteriorated. The pathological morphology of the spinal cord became aggravated, but lessened 24 hours after reperfusion. However, the numbers of motor neurons and interneurons in the spinal cord gradually decreased. The expression of protein disulfide isomerase A3, stress-induced-phosphoprotein 1 and heat shock cognate protein 70 was induced by ischemia/reperfusion injury. The expression of these proteins increased within 12 hours after reperfusion, and then decreased, reached a minimum at 24 hours, but subsequently increased again to similar levels seen at 6–12 hours, showing a characterization of induction-inhibition-induction. These three proteins were expressed only in cytoplasm but not in the nuclei. Moreover, the expression was higher in interneurons than in motor neurons, and the survival rate of interneurons was greater than that of motor neurons. It is assumed that the expression of stress-related proteins exhibited a protective effect on neurons.

Increased expression of stress inducible protein 1 in glioma-associated microglia/macrophages

Factors released by glioma-associated microglia/macrophages (GAMs) play an important role in the growth and infiltration of tumors. We have previously demonstrated that the co-chaperone stress-inducible protein 1 (STI1) secreted by microglia promotes proliferation and migration of human glioblastoma (GBM) cell lines in vitro. In the present study, in order to investigate the role of STI1 in a physiological context, we used a glioma model to evaluate STI1 expression in vivo. Here, we demonstrate that STI1 expression in both the tumor and in the infiltrating GAMs and lymphocytes significantly increased with tumor progression. Interestingly, high expression of STI1 was observed in macrophages and lymphocytes that infiltrated brain tumors, whereas STI1 expression in the circulating blood monocytes and lymphocytes remained unchanged. Our results correlate, for the first time, the expression of STI1 and glioma progression, and suggest that STI1 expression in GAMs and infiltrating lymphocytes is modulated by the brain tumor microenvironment.

STI1 antagonizes cytoskeleton collapse mediated by small GTPase Rnd1 and regulates neurite growth

Rnd proteins comprise a branch of the Rho family of small GTP-binding proteins, which have been implicated in rearrangements of the actin cytoskeleton and microtubule dynamics. Particularly in the nervous system, Rnd family proteins regulate neurite formation, dendrite development and axonal branching. A secreted form of the co-chaperone Stress-Inducible Protein 1 (STI1) has been described as a prion protein partner that is involved in several processes of the nervous system, such as neurite outgrowth, neuroprotection, astrocyte development, and the self-renewal of neural progenitor cells. We show that cytoplasmic STI1 directly interacts with the GTPase Rnd1. This interaction is specific for the Rnd1 member of the Rnd family. In the COS collapse assay, overexpression of STI1 prevents Rnd1-plexin-A1-mediated cytoskeleton retraction. In PC-12 cells, overexpression of STI1 enhances neurite outgrowth in cellular processes initially established by Rnd1. Therefore, we propose that STI1 participates in Rnd1-induced signal transduction pathways that are involved in the dynamics of the actin cytoskeleton.

Genome-wide association study of proneness to anger

Background

Community samples suggest that approximately 1 in 20 children and adults exhibit clinically significant anger, hostility, and aggression. Individuals with dysregulated emotional control have a greater lifetime burden of psychiatric morbidity, severe impairment in role functioning, and premature mortality due to cardiovascular disease.

Methods

With publically available data secured from dbGaP, we conducted a genome-wide association study of proneness to anger using the Spielberger State-Trait Anger Scale in the Atherosclerosis Risk in Communities (ARIC) study (n = 8,747).

Results

Subjects were, on average, 54 (range 45–64) years old at baseline enrollment, 47% (n = 4,117) were male, and all were of European descent by self-report. The mean Angry Temperament and Angry Reaction scores were 5.8±1.8 and 7.6±2.2. We observed a nominally significant finding (p = 2.9E-08, λ = 1.027 - corrected p_gc = 2.2E-07, λ = 1.0015) on chromosome 6q21 in the gene coding for the non-receptor protein-tyrosine kinase, Fyn.

Conclusions

Fyn interacts with NDMA receptors and inositol-1,4,5-trisphosphate (IP3)-gated channels to regulate calcium influx and intracellular release in the post-synaptic density. These results suggest that signaling pathways regulating intracellular calcium homeostasis, which are relevant to memory, learning, and neuronal survival, may in part underlie the expression of Angry Temperament.

The unconventional secretion of stress-inducible protein 1 by a heterogeneous population of extracellular vesicles

The co-chaperone stress-inducible protein 1 (STI1) is released by astrocytes, and has important neurotrophic properties upon binding to prion protein (PrP(C)). However, STI1 lacks a signal peptide and pharmacological approaches pointed that it does not follow a classical secretion mechanism. Ultracentrifugation, size exclusion chromatography, electron microscopy, vesicle labeling, and particle tracking analysis were used to identify three major types of extracellular vesicles (EVs) released from astrocytes with sizes ranging from 20-50, 100-200, and 300-400 nm. These EVs carry STI1 and present many exosomal markers, even though only a subpopulation had the typical exosomal morphology. The only protein, from those evaluated here, present exclusively in vesicles that have exosomal morphology was PrP(C). STI1 partially co-localized with Rab5 and Rab7 in endosomal compartments, and a dominant-negative for vacuolar protein sorting 4A (VPS4A), required for formation of multivesicular bodies (MVBs), impaired EV and STI1 release. Flow cytometry and PK digestion demonstrated that STI1 localized to the outer leaflet of EVs, and its association with EVs greatly increased STI1 activity upon PrP(C)-dependent neuronal signaling. These results indicate that astrocytes secrete a diverse population of EVs derived from MVBs that contain STI1 and suggest that the interaction between EVs and neuronal surface components enhances STI1-PrP(C) signaling.

Regulation of stress-inducible phosphoprotein 1 nuclear retention by protein inhibitor of activated STAT PIAS1

Stress-inducible phosphoprotein 1 (STI1), a cochaperone for Hsp90, has been shown to regulate multiple pathways in astrocytes, but its contributions to cellular stress responses are not fully understood. We show that in response to irradiation-mediated DNA damage stress STI1 accumulates in the nucleus of astrocytes. Also, STI1 haploinsufficiency decreases astrocyte survival after irradiation. Using yeast two-hybrid screenings we identified several nuclear proteins as STI1 interactors. Overexpression of one of these interactors, PIAS1, seems to be specifically involved in STI1 nuclear retention and in directing STI1 and Hsp90 to specific sub-nuclear regions. PIAS1 and STI1 co-immunoprecipitate and PIAS1 can function as an E3 SUMO ligase for STI. Using mass spectrometry we identified five SUMOylation sites in STI1. A STI1 mutant lacking these five sites is not SUMOylated, but still accumulates in the nucleus in response to increased expression of PIAS1, suggesting the possibility that a direct interaction with PIAS1 could be responsible for STI1 nuclear retention. To test this possibility, we mapped the interaction sites between PIAS1 and STI1 using yeast-two hybrid assays and surface plasmon resonance and found that a large domain in the N-terminal region of STI1 interacts with high affinity with amino acids 450-480 of PIAS1. Knockdown of PIAS1 in astrocytes impairs the accumulation of nuclear STI1 in response to irradiation. Moreover, a PIAS1 mutant lacking the STI1 binding site is unable to increase STI1 nuclear retention. Interestingly, in human glioblastoma multiforme PIAS1 expression is increased and we found a significant correlation between increased PIAS1 expression and STI1 nuclear localization. These experiments provide evidence that direct interaction between STI1 and PIAS1 is involved in the accumulation of nuclear STI1. This retention mechanism could facilitate nuclear chaperone activity.

Stress-inducible phosphoprotein 1 has unique cochaperone activity during development and regulates cellular response to ischemia via the prion protein

Stress-inducible phosphoprotein 1 (STI1) is part of the chaperone machinery, but it also functions as an extracellular ligand for the prion protein. However, the physiological relevance of these STI1 activities in vivo is unknown. Here, we show that in the absence of embryonic STI1, several Hsp90 client proteins are decreased by 50%, although Hsp90 levels are unaffected. Mutant STI1 mice showed increased caspase-3 activation and 50% impairment in cellular proliferation. Moreover, placental disruption and lack of cellular viability were linked to embryonic death by E10.5 in STI1-mutant mice. Rescue of embryonic lethality in these mutants, by transgenic expression of the STI1 gene, supported a unique role for STI1 during embryonic development. The response of STI1 haploinsufficient mice to cellular stress seemed compromised, and mutant mice showed increased vulnerability to ischemic insult. At the cellular level, ischemia increased the secretion of STI1 from wild-type astrocytes by 3-fold, whereas STI1 haploinsufficient mice secreted half as much STI1. Interesting, extracellular STI1 prevented ischemia-mediated neuronal death in a prion protein-dependent way. Our study reveals essential roles for intracellular and extracellular STI1 in cellular resilience.

Laminin-γ1 chain and stress inducible protein 1 synergistically mediate PrPC-dependent axonal growth via Ca2+ mobilization in dorsal root ganglia neurons

Prion protein (PrP(C)) is a cell surface glycoprotein that is abundantly expressed in nervous system. The elucidation of the PrP(C) interactome network and its significance on neural physiology is crucial to understanding neurodegenerative events associated with prion and Alzheimer's diseases. PrP(C) co-opts stress inducible protein 1/alpha7 nicotinic acetylcholine receptor (STI1/α7nAChR) or laminin/Type I metabotropic glutamate receptors (mGluR1/5) to modulate hippocampal neuronal survival and differentiation. However, potential cross-talk between these protein complexes and their role in peripheral neurons has never been addressed. To explore this issue, we investigated PrP(C)-mediated axonogenesis in peripheral neurons in response to STI1 and laminin-γ1 chain-derived peptide (Ln-γ1). STI1 and Ln-γ1 promoted robust axonogenesis in wild-type neurons, whereas no effect was observed in neurons from PrP(C) -null mice. PrP(C) binding to Ln-γ1 or STI1 led to an increase in intracellular Ca(2+) levels via distinct mechanisms: STI1 promoted extracellular Ca(2+) influx, and Ln-γ1 released calcium from intracellular stores. Both effects depend on phospholipase C activation, which is modulated by mGluR1/5 for Ln-γ1, but depends on, C-type transient receptor potential (TRPC) channels rather than α7nAChR for STI1. Treatment of neurons with suboptimal concentrations of both ligands led to synergistic actions on PrP(C)-mediated calcium response and axonogenesis. This effect was likely mediated by simultaneous binding of the two ligands to PrP(C). These results suggest a role for PrP(C) as an organizer of diverse multiprotein complexes, triggering specific signaling pathways and promoting axonogenesis in the peripheral nervous system.

The cellular form of the prion protein is involved in controlling cell cycle dynamics, self-renewal, and the fate of human embryonic stem cell differentiation

Prion protein (PrP(C) ), is a glycoprotein that is expressed on the cell surface. The current study examines the role of PrP(C) in early human embryogenesis using human embryonic stem cells (hESCs) and tetracycline-regulated lentiviral vectors that up-regulate or suppresses PrP(C) expression. Here, we show that expression of PrP(C) in pluripotent hESCs cultured under self-renewal conditions induced cell differentiation toward lineages of three germ layers. Silencing of PrP(C) in hESCs undergoing spontaneous differentiation altered the dynamics of the cell cycle and changed the balance between the lineages of the three germ layers, where differentiation toward ectodermal lineages was suppressed. Moreover, over-expression of PrP(C) in hESCs undergoing spontaneous differentiation inhibited differentiation toward lineages of all three germ layers and helped to preserve high proliferation activity. These results illustrate that PrP(C) is involved in key activities that dictate the status of hESCs including regulation of cell cycle dynamics, controlling the switch between self-renewal and differentiation, and determining the fate of hESCs differentiation. This study suggests that PrP(C) is at the crossroads of several signaling pathways that regulate the switch between preservation of or departure from the self-renewal state, control cell proliferation activity, and define stem cell fate.

Prion potency in stem cells biology

Prion protein (PrP) can be considered a pivotal molecule because it interacts with several partners to perform a diverse range of critical biological functions that might differ in embryonic and adult cells. In recent years, there have been major advances in elucidating the putative role of PrP in the basic biology of stem cells in many different systems. Here, we review the evidence indicating that PrP is a key molecule involved in driving different aspects of the potency of embryonic and tissue-specific stem cells in self-perpetuation and differentiation in many cell types. It has been shown that PrP is involved in stem cell self-renewal, controlling pluripotency gene expression, proliferation, and neural and cardiomyocyte differentiation. PrP also has essential roles in distinct processes that regulate tissue-specific stem cell biology in nervous and hematopoietic systems and during muscle regeneration. Results from our own investigations have shown that PrP is able to modulate self-renewal and proliferation in neural stem cells, processes that are enhanced by PrP interactions with stress inducible protein 1 (STI1). Thus, the available data reveal the influence of PrP in acting upon the maintenance of pluripotent status or the differentiation of stem cells from the early embryogenesis through adulthood.

Allosteric function and dysfunction of the prion protein

Transmissible spongiform encephalopathies (TSEs) are neurodegenerative diseases associated with progressive oligo- and multimerization of the prion protein (PrP(C)), its conformational conversion, aggregation and precipitation. We recently proposed that PrP(C) serves as a cell surface scaffold protein for a variety of signaling modules, the effects of which translate into wide-range functional consequences. Here we review evidence for allosteric functions of PrP(C), which constitute a common property of scaffold proteins. The available data suggest that allosteric effects among PrP(C) and its partners are involved in the assembly of multi-component signaling modules at the cell surface, impose upon both physiological and pathological conformational responses of PrP(C), and that allosteric dysfunction of PrP(C) has the potential to entail progressive signal corruption. These properties may be germane both to physiological roles of PrP(C), as well as to the pathogenesis of the TSEs and other degenerative/non-communicable diseases.

Enhanced neural progenitor/stem cells self-renewal via the interaction of stress-inducible protein 1 with the prion protein

Prion protein (PrP(C) ), when associated with the secreted form of the stress-inducible protein 1 (STI1), plays an important role in neural survival, neuritogenesis, and memory formation. However, the role of the PrP(C) -STI1 complex in the physiology of neural progenitor/stem cells is unknown. In this article, we observed that neurospheres cultured from fetal forebrain of wild-type (Prnp(+/+) ) and PrP(C) -null (Prnp(0/0) ) mice were maintained for several passages without the loss of self-renewal or multipotentiality, as assessed by their continued capacity to generate neurons, astrocytes, and oligodendrocytes. The homogeneous expression and colocalization of STI1 and PrP(C) suggest that they may associate and function as a complex in neurosphere-derived stem cells. The formation of neurospheres from Prnp(0/0) mice was reduced significantly when compared with their wild-type counterparts. In addition, blockade of secreted STI1, and its cell surface ligand, PrP(C) , with specific antibodies, impaired Prnp(+/+) neurosphere formation without further impairing the formation of Prnp(0/0) neurospheres. Alternatively, neurosphere formation was enhanced by recombinant STI1 application in cells expressing PrP(C) but not in cells from Prnp(0/0) mice. The STI1-PrP(C) interaction was able to stimulate cell proliferation in the neurosphere-forming assay, while no effect on cell survival or the expression of neural markers was observed. These data suggest that the STI1-PrP(C) complex may play a critical role in neural progenitor/stem cells self-renewal via the modulation of cell proliferation, leading to the control of the stemness capacity of these cells during nervous system development.

Mapping of endogenous morphine-like compounds in the adult mouse brain: Evidence of their localization in astrocytes and GABAergic cells

Endogenous morphine, morphine-6-glucuronide, and codeine, which are structurally identical to vegetal alkaloids, can be synthesized by mammalian cells from dopamine. However, the role of brain endogenous morphine and its derivative compounds is a matter of debate, and knowledge about its distribution is lacking. In this study, by using a validated antibody, we describe a precise mapping of endogenous morphine-like compounds (morphine and/or its glucuronides and/or codeine) in the mouse brain. First, a mass spectrometry approach confirmed the presence of morphine and codeine in mouse brain, but also, of morphine-6-glucuronide and morphine-3-glucuronide representing two metabolites of morphine. Second, light microscopy allowed us to observe immunopositive cell somas and cytoplasmic processes throughout the mouse brain. Morphine-like immunoreactivity was present in various structures including the hippocampus, olfactory bulb, band of Broca, basal ganglia, and cerebellum. Third, by using confocal microscopy and immunofluroscence co-localization, we characterized cell types containing endogenous opiates. Interestingly, we observed that morphine-like immunoreactivity throughout the encephalon is mainly present in γ-aminobutyric acid (GABA)ergic neurons. Astrocytes were also labeled throughout the entire brain, in the cell body, in the cytoplasmic processes, and in astrocytic feet surrounding blood vessels. Finally, ultrastructural localization of morphine-like immunoreactivity was determined by electron microscopy and showed the presence of morphine-like label in presynaptic terminals in the cerebellum and postsynaptic terminals in the rest of the mouse brain. In conclusion, the presence of endogenous morphine-like compounds in brain regions not usually involved in pain modulation opens the exciting opportunity to extend the role and function of endogenous alkaloids far beyond their analgesic functions.

Genome-wide association study of the child behavior checklist dysregulation profile

OBJECTIVE

A potentially useful tool for understanding the distribution and determinants of emotional dysregulation in children is a Child Behavior Checklist profile, comprising the Attention Problems, Anxious/Depressed, and Aggressive Behavior clinical subscales (CBCL-DP). The CBCL-DP indexes a heritable trait that increases susceptibility for later psychopathology, including severe mood problems and aggressive behavior. We have conducted a genome-wide association study of the CBCL-DP in children with attention-deficit/hyperactivity disorder (ADHD).

METHOD

Families were ascertained at Massachusetts General Hospital and University of California, Los Angeles. Genotyping was conducted with the Illumina Human1M or Human1M-Duo BeadChip platforms. Genome-wide association analyses were conducted with the MQFAM multivariate extension of PLINK.

RESULTS

CBCL data were available for 341 ADHD offspring from 339 ADHD affected trio families from the UCLA (N = 128) and the MGH (N = 213) sites. We found no genome-wide statistically significant associations but identified several plausible candidate genes among findings at p < 5E-05: TMEM132D, LRRC7, SEMA3A, ALK, and STIP1.

CONCLUSIONS

We found suggestive evidence for developmentally expressed genes operant in hippocampal dependent memory and learning with the CBCL-DP.

Characterization of TcSTI-1, a homologue of stress-induced protein-1, in Trypanosoma cruzi

The life cycle of the protozoan Trypanosoma cruzi exposes it to several environmental stresses in its invertebrate and vertebrate hosts. Stress conditions are involved in parasite differentiation, but little is known about the stress response proteins involved. We report here the first characterization of stress-induced protein-1 (STI-1) in T. cruzi (TcSTI-1). This co-chaperone is produced in response to stress and mediates the formation of a complex between the stress proteins HSP70 and HSP90 in other organisms. Despite the similarity of TcSTI-1 to STI-1 proteins in other organisms, its expression profile in response to various stress conditions, such as heat shock, acidic pH or nutrient starvation, is quite different. Neither polysomal mRNA nor protein levels changed in exponentially growing epimastigotes cultured under any of the stress conditions studied. Increased levels of TcSTI-1 were observed in epimastigotes subjected to nutritional stress in the late growth phase. Co-immunoprecipitation assays revealed an association between TcSTI-1 and TcHSP70 in T. cruzi epimastigotes. Immunolocalization demonstrated that TcSTI-1 was distributed throughout the cytoplasm and there was some colocalization of TcSTI-1 and TcHSP70 around the nucleus. Thus, TcSTI-1 associates with TcHSP70 and TcSTI-1 expression is induced when the parasites are subjected to stress conditions during specific growth phase.