Stress biology: Complexity and multifariousness in health and disease

Preserving and regulating cellular homeostasis in the light of changing environmental conditions or developmental processes is of pivotal importance for single cellular and multicellular organisms alike. To counteract an imbalance in cellular homeostasis transcriptional programs evolved, called the heat shock response, unfolded protein response, and integrated stress response, that act cell-autonomously in most cells but in multicellular organisms are subjected to cell-nonautonomous regulation. These transcriptional programs downregulate the expression of most genes but increase the expression of heat shock genes, including genes encoding molecular chaperones and proteases, proteins involved in the repair of stress-induced damage to macromolecules and cellular structures. Sixty-one years after the discovery of the heat shock response by Ferruccio Ritossa, many aspects of stress biology are still enigmatic. Recent progress in the understanding of stress responses and molecular chaperones was reported at the 12th International Symposium on Heat Shock Proteins in Biology, Medicine and the Environment in the Old Town Alexandria, VA, USA from 28th to 31st of October 2023.

Non-Essential Amino Acid Availability Influences Proteostasis and Breast Cancer Cell Survival During Proteotoxic Stress

Protein homeostasis (proteostasis) regulates tumor growth and proliferation when cells are exposed to proteotoxic stress, such as during treatment with certain chemotherapeutics. Consequently, cancer cells depend to a greater extent on stress signaling, and require the integrated stress response (ISR), amino acid metabolism, and efficient protein folding and degradation pathways to survive. To define how these interconnected pathways are wired when cancer cells are challenged with proteotoxic stress, we investigated how amino acid abundance influences cell survival when Hsp70, a master proteostasis regulator, is inhibited. We previously demonstrated that cancer cells exposed to a specific Hsp70 inhibitor induce the ISR via the action of two sensors, GCN2 and PERK, in stress-resistant and sensitive cells, respectively. In resistant cells, the induction of GCN2 and autophagy supported resistant cell survival, yet the mechanism by which these events were induced remained unclear. We now report that amino acid availability reconfigures the proteostasis network. Amino acid supplementation, and in particular arginine addition, triggered cancer cell death by blocking autophagy. Consistent with the importance of amino acid availability, which when limited activates GCN2, resistant cancer cells succumbed when challenged with a potentiator for another amino acid sensor, mTORC1, in conjunction with Hsp70 inhibition.

IMPLICATIONS

These data position amino acid abundance, GCN2, mTORC1, and autophagy as integrated therapeutic targets whose coordinated modulation regulates the survival of proteotoxic-resistant breast cancer cells.

A campaign targeting a conserved Hsp70 binding site uncovers how subcellular localization is linked to distinct biological activities

The potential of small molecules to localize within subcellular compartments is rarely explored. To probe this question, we measured the localization of Hsp70 inhibitors using fluorescence microscopy. We found that even closely related analogs had dramatically different distributions, with some residing predominantly in the mitochondria and others in the ER. CRISPRi screens supported this idea, showing that different compounds had distinct chemogenetic interactions with Hsp70s of the ER (HSPA5/BiP) and mitochondria (HSPA9/mortalin) and their co-chaperones. Moreover, localization seemed to determine function, even for molecules with conserved binding sites. Compounds with distinct partitioning have distinct anti-proliferative activity in breast cancer cells compared with anti-viral activity in cellular models of Dengue virus replication, likely because different sets of Hsp70s are required in these processes. These findings highlight the contributions of subcellular partitioning and chemogenetic interactions to small molecule activity, features that are rarely explored during medicinal chemistry campaigns.

Single feature constrained manual registration method for Augmented Reality applications in gynecological laparoscopic interventions

Augmented Reality (AR) can avoid some of the drawbacks of Minimally Invasive Surgery and may provide opportunities for developing innovative tools to assist surgeons. In laparoscopic surgery, the achievement of easy and sufficiently accurate registration is an open challenge. This is particularly true in procedures, such as laparoscopic abdominal Sacro-Colpopexy, where there is a lack of a sufficient number of visible anatomical landmarks to be used as a reference for registration. In an attempt to address the above limitations, we developed and preliminarily testes a constrained manual procedure based on the identification of a single anatomical landmark in the laparoscopic images, and the intraoperative measurement of the laparoscope orientation. Tests in a rigid in-vitro environment show good accuracy (median error 2.4 mm obtained in about 4 min) and good preliminary feedback from the technical staff who tested the system. Further experimentation in a more realistic environment is needed to validate these positive results. Clinical Relevance - This paper provides a new registration method for the development of AR educational videos and AR-based navigation systems for laparoscopic interventions.

Abstract 1934: Modulation of protein homeostasis networks upon Hsp70 inhibition in cancer cells

Cellular protein homeostasis is tightly regulated by balancing protein synthesis, folding, and degradation. Cancer cells constantly modulate protein folding and degradation efficiency to survive and proliferate without accumulating toxic misfolded proteins under acute stress conditions, such as low oxygen and energy, and exposure to chemotherapeutic agents. Many cancers rely on the unfolded protein response (UPR) to cope with stress, which increases the expression of molecular chaperones and mitigates the accumulation of misfolded proteins. Thus, it is unsurprising that the Hsp70 molecular chaperone, which serves as a master regulator of proteostasis, is upregulated in many cancers. Increased Hsp70 correlates with metastasis formation and poor patient prognosis in different cancers, like breast cancer. To define the role of Hsp70 in cancer survival and identify how cancer cells compensate for chaperone-mediated proteotoxicity, we investigated the response to a specific Hsp70 inhibitor, MAL3-101, in breast cancer cells. We discovered that breast cancer cells bin into distinct groups when subjected to Hsp70 inhibition based on their sensitivity to the compound. Moreover, we demonstrate that resistant cells have higher autophagy levels compared to more sensitive lines. Autophagy was further induced by MAL3-101 in resistant breast cancer cells, as evidenced by the accumulation of both autophagy related genes and proteins, as well as by autophagic-like structures detected by confocal microscopy. These data suggest that resistance to Hsp70 inhibition arises from autophagy induction. We then discovered that Hsp70 inhibition induces the UPR pathway, triggering apoptosis in sensitive cells. In particular, the activation of the UPR transducer, PERK, is required to induce apoptosis in sensitive cells when Hsp70 was inhibited. Overall, our work positions autophagy as a critical compensatory mechanism when molecular chaperone function is overwhelmed and misfolded proteins accumulate. Furthermore, our findings delineate a distinct role of PERK in apoptosis induction upon Hsp70 inhibition, highlighting the interplay between the PERK, Hsp70, and autophagy.

Citation Format: Sara Sannino, Jeffrey L. Brodsky. Modulation of protein homeostasis networks upon Hsp70 inhibition in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1934.

Unique integrated stress response sensors regulate cancer cell susceptibility when Hsp70 activity is compromised

Molecular chaperones, such as Hsp70, prevent proteotoxicity and maintain homeostasis. This is perhaps most evident in cancer cells, which overexpress Hsp70 and thrive even when harboring high levels of misfolded proteins. To define the response to proteotoxic challenges, we examined adaptive responses in breast cancer cells in the presence of an Hsp70 inhibitor. We discovered that the cells bin into distinct classes based on inhibitor sensitivity. Strikingly, the most resistant cells have higher autophagy levels, and autophagy was maximally activated only in resistant cells upon Hsp70 inhibition. In turn, resistance to compromised Hsp70 function required the integrated stress response transducer, GCN2, which is commonly associated with amino acid starvation. In contrast, sensitive cells succumbed to Hsp70 inhibition by activating PERK. These data reveal an unexpected route through which breast cancer cells adapt to proteotoxic insults and position GCN2 and autophagy as complementary mechanisms to ensure survival when proteostasis is compromised.

Abstract 1232: Synergistic roles played by autophagy and Hsp70 in cancer cell survival

To avoid cell death, cancer cells adapt to extreme conditions. Chaperone upregulation, modulation of the unfolded protein response (UPR), and induction of protein degradation pathways are critical for cancer cell survival and metastasis in some cancers. Thus, it is not surprising that the molecular chaperone Hsp70 is upregulated in many cancers. For example, increased Hsp70 abundance correlates with metastasis formation and poor prognosis in breast cancer patients. We previously demonstrated that inhibition of Hsp70, by treating cells with a specific inhibitor known as MAL3-101, induces rhabdomyosarcoma cancer cell death due to induction of a UPR-mediated apoptotic response (Sabinis et al., 2016). Moreover, by taking advantage of a MAL3-101-resistant cell line, we established that protein degradation pathways act as a compensatory mechanism in MAL3-101 resistant rhabdomyosarcoma cells. In particular, we found that autophagy inhibition re-sensitized resistant cells to Hsp70 inhibition, suggesting that autophagy is a key compensatory mechanism for Hsp70 inhibition. Autophagy was further induced by MAL3-101 treatment in these cells, as evidenced by both autophagy related gene mRNA and protein accumulation as well as by autophagic-like structures detected by electron microscopy (Sannino et al., 2018). These data highlight a pro-survival role for autophagy induction upon exposure to an Hsp70 inhibitor in cancer, and provide a link between Hsp70, proteasome activity, the UPR, and autophagy in rhabdomyosarcoma. We next asked if other cancers might be dependent on Hsp70 activity and investigated the benefit of combined treatment with autophagy and/or proteasome inhibitors together with MAL3-101 in breast cancer cells. Our recent studies suggest that diverse breast cancer cell lines are either sensitive or resistant to Hsp70 inhibition. MAL3-101 resistant breast cancer cells have higher autophagy levels compared to MAL3-101 sensitive lines. Moreover, autophagy is upregulated upon Hsp70 inhibition in resistant breast cancer cells, again highlighting the potential benefit of combined treatment with autophagy and Hsp70 inhibitors. Overall, our work positions autophagy as a critical compensatory mechanism when molecular chaperone function is overwhelmed and misfolded proteins accumulate in cancer cells. Further investigations will reveal the potential for Hsp70 inhibitors and the role of protein degradation pathways in vivo in breast cancer.

Citation Format: Sara Sannino, Jeffrey L. Brodsky. Synergistic roles played by autophagy and Hsp70 in cancer cell survival [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1232.

Synthesis and Selective Functionalization of Thiadiazine 1,1-Dioxides with Efficacy in a Model of Huntington's Disease

The scope of the acid-mediated 3-component synthesis of thiadiazines was investigated. A selective functionalization of the six-membered heterocyclic core structure was accomplished by sequential alkylations, saponifications, and coupling reactions. Several new analogs of a dihydropyrimidinone Hsp70 chaperone agonist, MAL1-271, showed promising activity in a cell based model of Huntington's disease.

Abstract 4268: Protein folding pathway modulation upon Hsp70 inhibition in cancer cells

Cancer cells experience acute stress conditions such as low oxygen and energy, and exposure to toxic agents. To survive proliferate without accumulating toxic misfolded proteins, cancer cells constantly modulate protein homeostasis. Thus, it is not surprising that molecular chaperones, like Hsp70, as well as protein degradation pathways are upregulated in cancer cells compared to their normal counterparts. These data suggest that chaperones are potential targets for cancer therapy. We previously demonstrated the dependence of patient-driven rhabdomyosarcoma cell survival on cytoplasmic Hsp70 activity, thanks to the use of a specific Hsp70 inhibitor, MAL3-101. In particular, we discovered that MAL3-101-mediated Hsp70 inhibition activates the PERK arm of the unfolded protein response (UPR) that results in CHOP-dependent cell death (Sabinis et al., 2016). Moreover, by taking advantage of a MAL3-101-resistant cell line (RMS13-R), we recently determined which compensatory mechanism alters MAL3-101-driven cell death. We found that both endoplasmic reticulum-associated degradation (ERAD) and autophagy are upregulated in RMS13-R cells, underlying increased demand on two protein degradation pathways upon inhibition of Hsp70. However, only autophagy inhibition—but not inhibition of ERAD—re-sensitized RMS13-R cells to Hsp70 inhibition, suggesting that autophagy was the key compensatory mechanism for Hsp70 inhibition. Autophagy was further induced by MAL3-101 treatment in RMS13-R cells, as evidenced by an increase in the messages and proteins corresponding to key autophagy components as well as to the accumulation of autophagic-like structures detected by electron microscopy (Sannino et al., 2018). These data highlight a pro-survival role for autophagy induction upon exposure to an Hsp70 inhibitor in cancer, and provide a link between Hsp70, proteasomal degradation, UPR, and autophagy in rhabdomyosarcoma. We next asked if other cancer types might be sensitive to Hsp70 inhibition, and we investigated the potential benefit of combined treatment with autophagy and/or proteasome inhibitors together with MAL3-101. Specifically, we are investigating the effects of Hsp70 inhibition in breast cancer cells, a cancer type in which higher levels of Hsp70 correlate to increased metastasis and poor prognosis in patients. Our preliminary data suggest that HER2-expressing cells are less sensitive to MAL3-101-mediated Hsp70 inhibition and combinatory treatments including, MAL3-101 and autophagy inhibitors promoted HER2-breast cancer cell death. Further investigations will reveal the potential carcinogenic role of Hsp70 inhibitors in breast cancer treatment and highlight which pathways reduce proteotoxicity in different breast cancer subtypes.

Citation Format: Sara Sannino, Christopher J. Guerriero, Amit J. Sabnis, Jeffrey J. Bridsky. Protein folding pathway modulation upon Hsp70 inhibition in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4268.

Compensatory increases of select proteostasis networks after Hsp70 inhibition in cancer cells

Cancer cells thrive when challenged with proteotoxic stress by inducing components of the protein folding, proteasome, autophagy and unfolded protein response (UPR) pathways. Consequently, specific molecular chaperones have been validated as targets for anti-cancer therapies. For example, inhibition of Hsp70 family proteins (hereafter Hsp70) in rhabdomyosarcoma triggers UPR induction and apoptosis. To define how these cancer cells respond to compromised proteostasis, we compared rhabdomyosarcoma cells that were sensitive (RMS13) or resistant (RMS13-R) to the Hsp70 inhibitor MAL3-101. We discovered that endoplasmic reticulum-associated degradation (ERAD) and autophagy were activated in RMS13-R cells, suggesting that resistant cells overcome Hsp70 ablation by increasing misfolded protein degradation. Indeed, RMS13-R cells degraded ERAD substrates more rapidly than RMS cells and induced the autophagy pathway. Surprisingly, inhibition of the proteasome or ERAD had no effect on RMS13-R cell survival, but silencing of select autophagy components or treatment with autophagy inhibitors restored MAL3-101 sensitivity and led to apoptosis. These data indicate a route through which cancer cells overcome a chaperone-based therapy, define how cells can adapt to Hsp70 inhibition, and demonstrate the value of combined chaperone and autophagy-based therapies.This article has an associated First Person interview with the first author of the paper.

Abstract 2325: Protein homeostasis adaptation to Hsp70 inhibition in cancer

Cancer cells experience acute stress conditions due to their increased proliferation rate and synthesis of misfolded proteins. However, by modulating the mechanisms that control protein-folding, cancer cells avoid cell death. Thus, it is perhaps not surprising that molecular chaperones, like Hsp70, are upregulated in cancer cells compared to their normal counterparts. These data suggest that these chaperones are potential targets for cancer therapy. Previous work in our lab demonstrated the dependence of patient-driven rhabdomyosarcoma cell survival on cytoplasmic Hsp70 activity, thanks to the use of a specific Hsp70 inhibitor, MAL3-101. In particular, we discovered that treatment of on RMS13 cell line with an Hsp70 inhibitor, known as MAL3-101, activates the PERK driven unfolded protein response that results in CHOP-dependent cell death (Sabinis et al., 2016). Nevertheless, the mechanism underlying how Hsp70 inhibition triggered apoptosis was poorly understood. By taking advantage of a MAL3-101-resistant cell line (RMS13-R), we have now determined which compensatory mechanism alters MAL3-101-driven cell death. We found that both endoplasmic reticulum-associated degradation (ERAD) and autophagy are upregulated in RMS13-R cells, underlying the increased demand on two protein degradation pathways upon inhibition of Hsp70. Specifically, autophagy related genes were upregulated, and increased conversion of LC3BI to LC3BII and accumulation of LC3BII was detected in RMS13-R cells. Further experiments demonstrated that autophagy was further induced by MAL3-101 treatment in RMS13-R cells, as evidenced by an increase in the messages and proteins corresponding to key autophagy components. Finally, we discovered that only autophagy inhibition—but not inhibition of ERAD—re-sensitized RMS13-R cells to Hsp70 inhibition, which was apparent from an induction of apoptotic markers and cell death. These data highlight a pro-survival role for autophagy induction upon exposure to an Hsp70 inhibitor in cancer, and provide a link between Hsp70, proteasomal degradation, the unfolded protein response, and autophagy in rhabdomyosarcoma.

Citation Format: Sara Sannino, Christopher J. Guerriero, Amit J. Sabnis, Trever G. Bivona, Jeffrey L. Brodsky. Protein homeostasis adaptation to Hsp70 inhibition in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2325.

Targeting protein quality control pathways in breast cancer

The efficient production, folding, and secretion of proteins is critical for cancer cell survival. However, cancer cells thrive under stress conditions that damage proteins, so many cancer cells overexpress molecular chaperones that facilitate protein folding and target misfolded proteins for degradation via the ubiquitin-proteasome or autophagy pathway. Stress response pathway induction is also important for cancer cell survival. Indeed, validated targets for anti-cancer treatments include molecular chaperones, components of the unfolded protein response, the ubiquitin-proteasome system, and autophagy. We will focus on links between breast cancer and these processes, as well as the development of drug resistance, relapse, and treatment.

N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

N-acetyl-l-cysteine (NAC) exhibits protective properties in brain injury models and has undergone a number of clinical trials. Most studies of NAC have focused on neurons. However, neuroprotection may be complemented by the protection of astrocytes because healthier astrocytes can better support the viability of neurons. Here, we show that NAC can protect astrocytes against protein misfolding stress (proteotoxicity), the hallmark of neurodegenerative disorders. Although NAC is thought to be a glutathione precursor, NAC protected primary astrocytes from the toxicity of the proteasome inhibitor MG132 without eliciting any increase in glutathione. Furthermore, glutathione depletion failed to attenuate the protective effects of NAC. MG132 elicited a robust increase in the folding chaperone heat shock protein 70 (Hsp70), and NAC mitigated this effect. Nevertheless, three independent inhibitors of Hsp70 function ablated the protective effects of NAC, suggesting that NAC may help preserve Hsp70 chaperone activity and improve protein quality control without need for Hsp70 induction. Consistent with this view, NAC abolished an increase in ubiquitinated proteins in MG132-treated astrocytes. However, NAC did not affect the loss of proteasome activity in response to MG132, demonstrating that it boosted protein homeostasis and cell viability without directly interfering with the efficacy of this proteasome inhibitor. The thiol-containing molecules l-cysteine and d-cysteine both mimicked the protective effects of NAC, whereas the thiol-lacking molecule N-acetyl-S-methyl-l-cysteine failed to exert protection or blunt the rise in ubiquitinated proteins. Collectively, these findings suggest that the thiol group in NAC is required for its effects on glial viability and protein quality control.

Abstract 4503: Role of ER-associated degradation in rhabdomyosarcoma

Due to their higher proliferation rate, most cancers experience impaired ATP generation, hypoxia, hypoglycemia, and increased genetic mutations that may perturb cellular and protein homeostasis. Persistent stress conditions induce the unfolded protein response (UPR) as well as increased expression of molecular chaperones, such as Hsp70, to modulate cell fate. Our recent studies demonstrate how perturbing cytosolic Hsp70 activity with a small molecule modulator, MAL3-101, induces rhabdomyosarcoma cell (RMS13) death, patient-derived cells of one of the most common soft-tissue cancers in children. MAL3-101 addition activates PERK- and CHOP-dependent RMS13 cell death in a dose dependent manner (Sabnis et al., PNAS, 2016). To identify the mechanism that links UPR-triggered cell death and cytosolic Hsp70 inhibition, an isogenic MAL3-101-resistant cell line was generated (MAR4C). Even though both RMS13 and MAR4C cells were equally sensitive to a diverse panel of therapeutic compounds, we now find that they have different efficiencies of ER-associated degradation (ERAD), a quality control pathway that degrades misfolded proteins in the secretory pathway and that lessens proteotioxic stress. Specifically, MAR4C cells remove both soluble and membrane associated ERAD substrates faster than RMS13 cells and possess increased levels of ubiquitinated proteins upon proteasomal inhibition. These data suggest that higher ERAD efficiency is required for MAR4C cell survival upon Hsp70 inhibition and highlight an unexpected link between cytosolic Hsp70 inhibition and the ERAD pathway in cancer cells. Moreover, RNAseq analysis suggests that select redox-related ER quality control chaperones are differentially expressed between MAR4C and RMS13 cells, and lower levels of the BiP and PDI chaperones and Peroxiredoxin 4 are found in MAR4C cells. Because new therapeutic agents as well as reliable biomarkers are critically needed in rhabdomyosarcoma and other cancers, this study sheds light on one mechanism of cancer pathogenesis and suggests that different cancer subtypes modulate ER quality protein quality uniquely.

Citation Format: Sara Sannino, Christopher J. Guerriero, Jeffrey L. Brodsky. Role of ER-associated degradation in rhabdomyosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4503. doi:10.1158/1538-7445.AM2017-4503

Effects of alpha1-blockers on urodynamic parameters of bladder outlet obstruction in patients with lower urinary tract symptoms suggestive of benign prostatic enlargement: a review

α1-adrenergic receptors blockers (ABs) are recommended as first-line medical therapy in men with Lower Urinary Tract Symptoms suggestive of Benign Prostatic Enlargement (LUTS/BPE). Available ABs include: terazosin, doxazosin, tamsulosin, naftopidil, alfuzosin and silodosin. These agents have different profiles of selectivity for α1-adrenergic receptors subtypes. All these agents are efficacious in improving both storage and voiding LUTS. In recent years the efficacy of ABs in improving urodynamic parameters of bladder outlet obstruction (BOO) has been questioned. We reviewed literature evidences about the effects of available ABs on invasive urodynamic parameters of BOO in men with LUTS/BPE. The impact of ABs therapy on urodynamic parameters indicative of BOO has been evaluated for all currently approved drugs. Available data demonstrate improvements in terms of both free uroflowmetry and pressure-flow parameters. While the impact of ABs on maximum urinary flow is clinically modest, the improvement of detrusor pressure at maximum urinary flow is more robust. Only few studies exist that directly compare the urodynamic effects of a small number of ABs. According to these studies there are no differences among ABs in terms of urodynamic efficacy. Indirect comparison of ABs suggests greater effectiveness of silodosin in terms of detrusor pressure at maximum urinary flow reduction. Studies that stratified populations based upon the degree of obstruction at baseline demonstrated greater urodynamic changes in patients with baseline BOO with respect to the unobstructed patients. Globally, the quality of studies available is low and there is considerable heterogeneity among studies.

Proteostasis and "redoxtasis" in the secretory pathway: Tales of tails from ERp44 and immunoglobulins

In multicellular organisms, some cells are given the task of secreting huge quantities of proteins. To comply with their duty, they generally equip themselves with a highly developed endoplasmic reticulum (ER) and downstream organelles in the secretory pathway. These professional secretors face paramount proteostatic challenges in that they need to couple efficiency and fidelity in their secretory processes. On one hand, stringent quality control (QC) mechanisms operate from the ER onward to check the integrity of the secretome. On the other, the pressure to secrete can be overwhelming, as for instance on antibody-producing cells during infection. Maintaining homeostasis is particularly hard when the products to be released contain disulfide bonds, because oxidative folding entails production of reactive oxygen species. How are redox homeostasis ("redoxtasis") and proteostasis maintained despite the massive fluxes of cargo proteins traversing the pathway? Here we describe recent findings on how ERp44, a multifunctional chaperone of the secretory pathway, can modulate these processes integrating protein QC, redoxtasis, and calcium signaling.

A dynamic study of protein secretion and aggregation in the secretory pathway

Precise coordination of protein biogenesis, traffic and homeostasis within the early secretory compartment (ESC) is key for cell physiology. As a consequence, disturbances in these processes underlie many genetic and chronic diseases. Dynamic imaging methods are needed to follow the fate of cargo proteins and their interactions with resident enzymes and folding assistants. Here we applied the Halotag labelling system to study the behavior of proteins with different fates and roles in ESC: a chaperone, an ERAD substrate and an aggregation-prone molecule. Exploiting the Halo property of binding covalently ligands labelled with different fluorochromes, we developed and performed non-radioactive pulse and chase assays to follow sequential waves of proteins in ESC, discriminating between young and old molecules at the single cell level. In this way, we could monitor secretion and degradation of ER proteins in living cells. We can also follow the biogenesis, growth, accumulation and movements of protein aggregates in the ESC. Our data show that protein deposits within ESC grow by sequential apposition of molecules up to a given size, after which novel seeds are detected. The possibility of using ligands with distinct optical and physical properties offers a novel possibility to dynamically follow the fate of proteins in the ESC.

Progressive quality control of secretory proteins in the early secretory compartment by ERp44

ERp44 is a pH-regulated chaperone of the secretory pathway. In the acidic milieu of the Golgi, its C-terminal tail changes conformation, simultaneously exposing the substrate-binding site for cargo capture and the RDEL motif for ER retrieval through interactions with cognate receptors. Protonation of cysteine 29 in the active site allows tail movements in vitro and in vivo. Here, we show that conserved histidine residues in the C-terminal tail also regulate ERp44 in vivo. Mutants lacking these histidine residues retain substrates more efficiently. Surprisingly, they are also O-glycosylated and partially secreted. Co-expression of client proteins prevents secretion of the histidine mutants, forcing tail opening and RDEL accessibility. Client-induced RDEL exposure allows retrieval of proteins from distinct stations along the secretory pathway, as indicated by the changes in O-glycosylation patterns upon overexpression of different partners. The ensuing gradients might help to optimize folding and assembly of different cargoes. Endogenous ERp44 is O-glycosylated and secreted by human primary endometrial cells, suggesting possible pathophysiological roles of these processes.

Chronic and acute intranasal oxytocin produce divergent social effects in mice

Intranasal administration of oxytocin (OXT) might be a promising new adjunctive therapy for mental disorders characterized by social behavioral alterations such as autism and schizophrenia. Despite promising initial studies in humans, it is not yet clear the specificity of the behavioral effects induced by chronic intranasal OXT and if chronic intranasal OXT could have different effects compared with single administration. This is critical for the aforementioned chronic mental disorders that might potentially involve life-long treatments. As a first step to address these issues, here we report that chronic intranasal OXT treatment in wild-type C57BL/6J adult mice produced a selective reduction of social behaviors concomitant to a reduction of the OXT receptors throughout the brain. Conversely, acute intranasal OXT treatment produced partial increases in social behaviors towards opposite-sex novel-stimulus female mice, while on the other hand, it decreased social exploration of same-sex novel stimulus male mice, without affecting social behavior towards familiar stimulus male mice. Finally, prolonged exposure to intranasal OXT treatments did not alter, in wild-type animals, parameters of general health such as body weight, locomotor activity, olfactory and auditory functions, nor parameters of memory and sensorimotor gating abilities. These results indicate that a prolonged over-stimulation of a 'healthy' oxytocinergic brain system, with no inherent deficits in social interaction and normal endogenous levels of OXT, results in specific detrimental effects in social behaviors.

COMT Genetic Reduction Produces Sexually Divergent Effects on Cortical Anatomy and Working Memory in Mice and Humans

Genetic variations in catechol-O-methyltransferase (COMT) that modulate cortical dopamine have been associated with pleiotropic behavioral effects in humans and mice. Recent data suggest that some of these effects may vary among sexes. However, the specific brain substrates underlying COMT sexual dimorphisms remain unknown. Here, we report that genetically driven reduction in COMT enzyme activity increased cortical thickness in the prefrontal cortex (PFC) and postero-parieto-temporal cortex of male, but not female adult mice and humans. Dichotomous changes in PFC cytoarchitecture were also observed: reduced COMT increased a measure of neuronal density in males, while reducing it in female mice. Consistent with the neuroanatomical findings, COMT-dependent sex-specific morphological brain changes were paralleled by divergent effects on PFC-dependent working memory in both mice and humans. These findings emphasize a specific sex-gene interaction that can modulate brain morphological substrates with influence on behavioral outcomes in healthy subjects and, potentially, in neuropsychiatric populations.

Automatic visual tracking and social behaviour analysis with multiple mice

Social interactions are made of complex behavioural actions that might be found in all mammalians, including humans and rodents. Recently, mouse models are increasingly being used in preclinical research to understand the biological basis of social-related pathologies or abnormalities. However, reliable and flexible automatic systems able to precisely quantify social behavioural interactions of multiple mice are still missing. Here, we present a system built on two components. A module able to accurately track the position of multiple interacting mice from videos, regardless of their fur colour or light settings, and a module that automatically characterise social and non-social behaviours. The behavioural analysis is obtained by deriving a new set of specialised spatio-temporal features from the tracker output. These features are further employed by a learning-by-example classifier, which predicts for each frame and for each mouse in the cage one of the behaviours learnt from the examples given by the experimenters. The system is validated on an extensive set of experimental trials involving multiple mice in an open arena. In a first evaluation we compare the classifier output with the independent evaluation of two human graders, obtaining comparable results. Then, we show the applicability of our technique to multiple mice settings, using up to four interacting mice. The system is also compared with a solution recently proposed in the literature that, similarly to us, addresses the problem with a learning-by-examples approach. Finally, we further validated our automatic system to differentiate between C57B/6J (a commonly used reference inbred strain) and BTBR T+tf/J (a mouse model for autism spectrum disorders). Overall, these data demonstrate the validity and effectiveness of this new machine learning system in the detection of social and non-social behaviours in multiple (>2) interacting mice, and its versatility to deal with different experimental settings and scenarios.

COMT as a drug target for cognitive functions and dysfunctions

Catechol-O-methyltransferase (COMT) is a promising target for modulation of cognitive functions and dysfunctions. COMT dominates the regulation of dopamine metabolism in the prefrontal cortex. Thus, COMT effects are particularly evident in prefrontal cortex-dependent cognitive functions including executive control, working memory, attentional control and long-term memory. This has been determined by both genetic and pharmacological studies that we will highlight in the present review. In particular, we will discuss how common functional variants of the COMT gene may predict individual variation in selective cognitive abilities and vulnerability to cognitive deficits that characterize several neuropsychiatric disorders. Moreover, COMT genetic variants represent one source of individual differences in the cognitive responses to medications such as those used in psychiatric illnesses. COMT genetic testing may then predict some cognitive dysfunctions often seen in certain psychiatric illnesses even from presymptomatic stages and the efficacy/dosage of drugs used to treat them. The consideration of COMT-dependent differences may be important for the development of more efficient personalized healthcare.

Role of the dorsal hippocampus in object memory load

The dorsal hippocampus is crucial for mammalian spatial memory, but its exact role in item memory is still hotly debated. Recent evidence in humans suggested that the hippocampus might be selectively involved in item short-term memory to deal with an increasing memory load. In this study, we sought to test this hypothesis. To this aim we developed a novel behavioral procedure to study object memory load in mice by progressively increasing the stimulus set size in the spontaneous object recognition task. Using this procedure, we demonstrated that naive mice have a memory span, which is the number of elements they can remember for a short-time interval, of about six objects. Then, we showed that excitotoxic selective lesions of the dorsal hippocampus did not impair novel object discrimination in the condition of low memory load. In contrast, the same lesion impaired novel object discrimination in the high memory load condition, and reduced the object memory span to four objects. These results have important heuristic and clinical implications because they open new perspective toward the understanding of the role of the hippocampus in item memory and in memory span deficits occurring in human pathologies, such as Alzheimer's disease and schizophrenia.