Poly(A) tail length of neurohypophysial hormones is shortened under endoplasmic reticulum stress

Differentiation of human induced pluripotent stem cells into hypothalamic vasopressin neurons with minimal exogenous signals and partial conversion to the naive state

Familial neurohypophyseal diabetes insipidus (FNDI) is a degenerative disease of vasopressin (AVP) neurons. Studies in mouse in vivo models indicate that accumulation of mutant AVP prehormone is associated with FNDI pathology. However, studying human FNDI pathology in vivo is technically challenging. Therefore, an in vitro human model needs to be developed. When exogenous signals are minimized in the early phase of differentiation in vitro, mouse embryonic stem cells (ESCs)/induced pluripotent stem cells (iPSCs) differentiate into AVP neurons, whereas human ESCs/iPSCs die. Human ESCs/iPSCs are generally more similar to mouse epiblast stem cells (mEpiSCs) compared to mouse ESCs. In this study, we converted human FNDI-specific iPSCs by the naive conversion kit. Although the conversion was partial, we found improved cell survival under minimal exogenous signals and differentiation into rostral hypothalamic organoids. Overall, this method provides a simple and straightforward differentiation direction, which may improve the efficiency of hypothalamic differentiation.

Oxytocin and Related Peptide Hormones: Candidate Anti-Inflammatory Therapy in Early Stages of Sepsis

Sepsis is a potentially life-threatening systemic inflammatory syndrome characterized by dysregulated host immunological responses to infection. Uncontrolled immune cell activation and exponential elevation in circulating cytokines can lead to sepsis, septic shock, multiple organ dysfunction syndrome, and death. Sepsis is associated with high re-hospitalization and recovery may be incomplete, with long term sequelae including post-sepsis syndrome. Consequently, sepsis continues to be a leading cause of morbidity and mortality across the world. In our recent review of human chorionic gonadotropin (hCG), we noted that its major properties including promotion of fertility, parturition, and lactation were described over a century ago. By contrast, the anti-inflammatory properties of this hormone have been recognized only more recently. Vasopressin, a hormone best known for its anti-diuretic effect, also has anti-inflammatory actions. Surprisingly, vasopressin's close cousin, oxytocin, has broader and more potent anti-inflammatory effects than vasopressin and a larger number of pre-clinical studies supporting its potential role in limiting sepsis-associated organ damage. This review explores possible links between oxytocin and related octapeptide hormones and sepsis-related modulation of pro-inflammatory and anti-inflammatory activities.

Oxytocin Signaling Pathway: From Cell Biology to Clinical Implications

BACKGROUND

In addition to the well-known role played in lactation and parturition, Oxytocin (OT) and OT receptor (OTR) are involved in many other aspects such as the control of maternal and social behavior, the regulation of the growth of the neocortex, the maintenance of blood supply to the cortex, the stimulation of limbic olfactory area to mother-infant recognition bond, and the modulation of the autonomic nervous system via the vagal pathway. Moreover, OT and OTR show antiinflammatory, anti-oxidant, anti-pain, anti-diabetic, anti-dyslipidemic and anti-atherogenic effects.

OBJECTIVE

The aim of this narrative review is to summarize the main data coming from the literature dealing with the role of OT and OTR in physiology and pathologic conditions focusing on the most relevant aspects.

METHODS

Appropriate keywords and MeSH terms were identified and searched in Pubmed. Finally, references of original articles and reviews were examined.

RESULTS

We report the most significant and updated data on the role played by OT and OTR in physiology and different clinical contexts.

CONCLUSION

Emerging evidence indicates the involvement of OT system in several pathophysiological mechanisms influencing brain anatomy, cognition, language, sense of safety and trust and maternal behavior, with the possible use of exogenous administered OT in the treatment of specific neuropsychiatric conditions. Furthermore, it modulates pancreatic β-cell responsiveness and lipid metabolism leading to possible therapeutic use in diabetic and dyslipidemic patients and for limiting and even reversing atherosclerotic lesions.

Endoplasmic reticulum chaperone BiP/GRP78 knockdown leads to autophagy and cell death of arginine vasopressin neurons in mice

The immunoglobulin heavy chain binding protein (BiP), also referred to as 78-kDa glucose-regulated protein (GRP78), is a pivotal endoplasmic reticulum (ER) chaperone which modulates the unfolded protein response under ER stress. Our previous studies showed that BiP is expressed in arginine vasopressin (AVP) neurons under non-stress conditions and that BiP expression is upregulated in proportion to the increased AVP expression under dehydration. To clarify the role of BiP in AVP neurons, we used a viral approach in combination with shRNA interference for BiP knockdown in mouse AVP neurons. Injection of a recombinant adeno-associated virus equipped with a mouse AVP promoter and BiP shRNA cassette provided specific BiP knockdown in AVP neurons of the supraoptic (SON) and paraventricular nuclei (PVN) in mice. AVP neuron-specific BiP knockdown led to ER stress and AVP neuronal loss in the SON and PVN, resulting in increased urine volume due to lack of AVP secretion. Immunoelectron microscopy of AVP neurons revealed that autophagy was activated through the process of AVP neuronal loss, whereas no obvious features characteristic of apoptosis were observed. Pharmacological inhibition of autophagy by chloroquine exacerbated the AVP neuronal loss due to BiP knockdown, indicating a protective role of autophagy in AVP neurons under ER stress. In summary, our results demonstrate that BiP is essential for the AVP neuron system.

Degradation of Mutant Protein Aggregates within the Endoplasmic Reticulum of Vasopressin Neurons

Misfolded or unfolded proteins in the ER are said to be degraded only after translocation or isolation from the ER. Here, we describe a mechanism by which mutant proteins are degraded within the ER. Aggregates of mutant arginine vasopressin (AVP) precursor were confined to ER-associated compartments (ERACs) connected to the ER in AVP neurons of a mouse model of familial neurohypophysial diabetes insipidus. The ERACs were enclosed by membranes, an ER chaperone and marker protein of phagophores and autophagosomes were expressed around the aggregates, and lysosomes fused with the ERACs. Moreover, lysosome-related molecules were present within the ERACs, and aggregate degradation within the ERACs was dependent on autophagic-lysosomal activity. Thus, we demonstrate that protein aggregates can be degraded by autophagic-lysosomal machinery within specialized compartments of the ER.

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Mutant AVP precursors are confined to ERACs connected to the ER of FNDI AVP neurons

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Lysosomes fuse with ERACs surrounded by phagophore-like membranes

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Lysosome-related molecules are localized within ERACs

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Rapamycin reduces and chloroquine increases protein aggregate accumulation in ERACs

Forty-One Individuals With Mutations in the AVP-NPII Gene Associated With Familial Neurohypophyseal Diabetes Insipidus

CONTEXT

Familial neurohypophyseal diabetes insipidus is a rare disease produced by a deficiency in the secretion of antidiuretic hormone and is caused by mutations in the arginine vasopressin gene.

OBJECTIVE

Clinical, biochemical, and genetic characterization of a group of patients clinically diagnosed with familial neurohypophyseal diabetes insipidus, 1 of the largest cohorts of patients with protein neurophysin II (AVP-NPII) gene alterations studied so far.

DESIGN

The AVP-NPII gene was screened for mutations by PCR followed by direct Sanger sequencing in 15 different unrelated families from Spain.

RESULTS

The 15 probands presented with polyuria and polydipsia as the most important symptoms at the time of diagnosis. In these patients, the disease was diagnosed at a median of 6 years of age. We observed 11 likely pathogenic variants. Importantly, 4 of the AVP-NPII variants were novel (p.(Tyr21Cys), p.(Gly45Ser), p.(Cys75Tyr), p.(Gly88Cys)).

CONCLUSIONS

Cytotoxicity seems to be due to consequences common to all the variants found in our cohort, which are not able to fold correctly and pass the quality control of the ER. In concordance, we found autosomal dominant familial neurohypophyseal diabetes insipidus in the 15 families studied.

Lessons from animal models of endocrine disorders caused by defects of protein folding in the secretory pathway

Most peptide hormones originate from secretory protein precursors synthesized within the endoplasmic reticulum (ER). In this specialized organelle, the newly-made prohormones must fold to their native state. Completion of prohormone folding usually occurs prior to migration through the secretory pathway, as unfolded/misfolded prohormones are retained by mechanisms collectively known as ER quality control. Not only do most monomeric prohormones need to fold properly, but many also dimerize or oligomerize within the ER. If oligomerization occurs before completion of monomer folding then when a poorly folded peptide prohormone is retained by quality control mechanisms, it may confer ER retention upon its oligomerization partners. Conversely, oligomerization between well-folded and improperly folded partners might help to override ER quality control, resulting in rescue of misfolded forms. Both scenarios appear to be possible in different animal models of endocrine disorders caused by genetic defects of protein folding in the secretory pathway. In this paper, we briefly review three such conditions, including familial neurohypophyseal diabetes insipidus, insulin-deficient diabetes mellitus, and hypothyroidism with defective thyroglobulin.

Therapeutic Potential of Oxytocin in Atherosclerotic Cardiovascular Disease: Mechanisms and Signaling Pathways

Coronary artery disease (CAD) is a major cardiovascular disease responsible for high morbidity and mortality worldwide. The major pathophysiological basis of CAD is atherosclerosis in association with varieties of immunometabolic disorders that can suppress oxytocin (OT) receptor (OTR) signaling in the cardiovascular system (CVS). By contrast, OT not only maintains cardiovascular integrity but also has the potential to suppress and even reverse atherosclerotic alterations and CAD. These protective effects of OT are associated with its protection of the heart and blood vessels from immunometabolic injuries and the resultant inflammation and apoptosis through both peripheral and central approaches. As a result, OT can decelerate the progression of atherosclerosis and facilitate the recovery of CVS from these injuries. At the cellular level, the protective effect of OT on CVS involves a broad array of OTR signaling events. These signals mainly belong to the reperfusion injury salvage kinase pathway that is composed of phosphatidylinositol 3-kinase-Akt-endothelial nitric oxide synthase cascades and extracellular signal-regulated protein kinase 1/2. Additionally, AMP-activated protein kinase, Ca²⁺/calmodulin-dependent protein kinase signaling and many others are also implicated in OTR signaling in the CVS protection. These signaling events interact coordinately at many levels to suppress the production of inflammatory cytokines and the activation of apoptotic pathways. A particular target of these signaling events is endoplasmic reticulum (ER) stress and mitochondrial oxidative stress that interact through mitochondria-associated ER membrane. In contrast to these protective effects and machineries, rare but serious cardiovascular disturbances were also reported in labor induction and animal studies including hypotension, reflexive tachycardia, coronary spasm or thrombosis and allergy. Here, we review our current understanding of the protective effect of OT against varieties of atherosclerotic etiologies as well as the approaches and underlying mechanisms of these effects. Moreover, potential cardiovascular disturbances following OT application are also discussed to avoid unwanted effects in clinical trials of OT usages.

Sequestosome 1 (SQSTM1/p62) maintains protein folding capacity under endoplasmic reticulum stress in mouse hypothalamic organotypic culture

Sequestosome 1 (SQSTM1) also known as ubiquitin-binding protein p62 (p62) is a cargo protein involved in the degradation of misfolded proteins via selective autophagy. Disruption of autophagy and resulting accumulation of misfolded proteins in the endoplasmic reticulum (ER) leads to ER stress. ER stress is implicated in several neurodegenerative diseases and obesity. As knockout of p62 (p62KO) reportedly induces obesity in mice, we examined how p62 contributes to ER stress and the ensuing unfolded protein response (UPR) in hypothalamus using mouse organotypic cultures in the present study. Cultures from p62KO mice showed significantly reduced formation of LC3-GFP puncta, an index of autophagosome formation, in response to the chemical ER stressor thapsigargin compared to wild-type (WT) cultures. Hypothalamic cultures from p62KO mice exhibited higher basal expression of the UPR/ER stress markers CHOP mRNA and ATF4 mRNA than WT cultures. Thapsigargin enhanced CHOP, ATF4, and BiP mRNA as well as p-eIF2α protein expression in both WT and p62KO cultures, but all peak values were greater in p62KO cultures. A proteasome inhibitor increased p62 expression in WT cultures and upregulated the UPR/ER stress markers CHOP mRNA and ATF4 mRNA in both genotypes, but to a greater extent in p62KO cultures. Therefore, p62 deficiency disturbed autophagosome formation and enhanced both basal and chemically induced ER stress, suggesting that p62 serves to prevent ER stress in mouse hypothalamus by maintaining protein folding capacity.

Endoplasmic Reticulum (ER) Stress and Endocrine Disorders

The endoplasmic reticulum (ER) is the organelle where secretory and membrane proteins are synthesized and folded. Unfolded proteins that are retained within the ER can cause ER stress. Eukaryotic cells have a defense system called the “unfolded protein response” (UPR), which protects cells from ER stress. Cells undergo apoptosis when ER stress exceeds the capacity of the UPR, which has been revealed to cause human diseases. Although neurodegenerative diseases are well-known ER stress-related diseases, it has been discovered that endocrine diseases are also related to ER stress. In this review, we focus on ER stress-related human endocrine disorders. In addition to diabetes mellitus, which is well characterized, several relatively rare genetic disorders such as familial neurohypophyseal diabetes insipidus (FNDI), Wolfram syndrome, and isolated growth hormone deficiency type II (IGHD2) are discussed in this article.

Induced pluripotent stem cells derived from a patient with autosomal dominant familial neurohypophyseal diabetes insipidus caused by a variant in the AVP gene

Autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI) is caused by variants in the arginine vasopressin (AVP) gene. Here we report the generation of induced pluripotent stem cells (iPSCs) from a 42-year-old man carrying an adFNDI causing variant in exon 1 of the AVP gene using lentivirus-mediated nuclear reprogramming. The iPSCs carried the expected variant in the AVP gene. Furthermore, the iPSCs expressed pluripotency markers; displayed in vitro differentiation potential to the three germ layers and had a normal karyotype consistent with the original fibroblasts. This iPSC line is useful in future studies focusing on the pathogenesis of adFNDI.

Unfolded protein response in hypothalamic cultures of wild-type and ATF6α-knockout mice

Recent studies suggest that endoplasmic reticulum (ER) stress in the hypothalamus could affect systemic homeostatic regulation in areas such as energy and water balance. Activating transcription factor 6α (ATF6α) is an ER stress transducer which increases the expression of ER chaperones and ER-associated degradation (ERAD) components under ER stress. In the present study, we examined the regulation of the unfolding protein response (UPR) in mouse hypothalamic cultures of wild-type (WT) and ATF6α(-/-) mice. Thapsigargin (TG), an ER stressor, significantly increased the mRNA expression of immunoglobulin heavy chain binding protein (BiP), spliced X-box binding protein 1 (XBP1), activating transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), and ERAD components, in hypothalamic cultures of WT mice with the same threshold (0.1μM) and similar time courses. On the other hand, TG-induced upregulation of BiP and CHOP as well as most ERAD-related genes, but not spliced XBP1 or ATF4, was attenuated in ATF6α(-/-) mice compared with WT mice. Our data suggest that all the UPR arms are activated similarly in the mouse hypothalamus under ER stress conditions, where ATF6α regulates the expression of ER chaperones, CHOP, and ERAD components.

Arginine vasopressin neuronal loss results from autophagy-associated cell death in a mouse model for familial neurohypophysial diabetes insipidus

Familial neurohypophysial diabetes insipidus (FNDI) characterized by progressive polyuria is mostly caused by mutations in the gene encoding neurophysin II (NPII), which is the carrier protein of the antidiuretic hormone, arginine vasopressin (AVP). Although accumulation of mutant NPII in the endoplasmic reticulum (ER) could be toxic for AVP neurons, the precise mechanisms of cell death of AVP neurons, reported in autopsy studies, remain unclear. Here, we subjected FNDI model mice to intermittent water deprivation (WD) in order to promote the phenotypes. Electron microscopic analyses demonstrated that, while aggregates are confined to a certain compartment of the ER in the AVP neurons of FNDI mice with water access ad libitum, they were scattered throughout the dilated ER lumen in the FNDI mice subjected to WD for 4 weeks. It is also demonstrated that phagophores, the autophagosome precursors, emerged in the vicinity of aggregates and engulfed the ER containing scattered aggregates. Immunohistochemical analyses revealed that expression of p62, an adapter protein between ubiquitin and autophagosome, was elicited on autophagosomal membranes in the AVP neurons, suggesting selective autophagy induction at this time point. Treatment of hypothalamic explants of green fluorescent protein (GFP)-microtubule-associated protein 1 light chain 3 (LC3) transgenic mice with an ER stressor thapsigargin increased the number of GFP-LC3 puncta, suggesting that ER stress could induce autophagosome formation in the hypothalamus of wild-type mice as well. The cytoplasm of AVP neurons in FNDI mice was occupied with vacuoles in the mice subjected to WD for 12 weeks, when 30–40% of AVP neurons are lost. Our data thus demonstrated that autophagy was induced in the AVP neurons subjected to ER stress in FNDI mice. Although autophagy should primarily be protective for neurons, it is suggested that the organelles including ER were lost over time through autophagy, leading to autophagy-associated cell death of AVP neurons.

Endoplasmic reticulum stress in vasopressin neurons of familial diabetes insipidus model mice: aggregate formation and mRNA poly(A) tail shortening

The immunoglobulin heavy chain binding protein (BiP) is an endoplasmic reticulum (ER) chaperone, which binds to newly synthesized secretory and transmembrane proteins to facilitate protein folding. BiP mRNA is expressed in the arginine vasopressin (AVP) neurons in the supraoptic nucleus of wild-type mice even in basal conditions, and the expression levels increase in response to dehydration. These data suggest that AVP neurons are subjected to ER stress. Familial neurohypophysial diabetes insipidus (FNDI) is caused by mutations in the gene locus of AVP. The mutant proteins could accumulate in the ER and possibly increase ER stress in the AVP neurons. We bred mice possessing a mutation causing FNDI, which manifested progressive polyuria, as do the patients with FNDI. Electron microscopic analyses demonstrated that aggregates accumulated in the ER of AVP neurons in FNDI mice. Despite polyuria, which could potentially induce dehydration, AVP mRNA expression was decreased in the supraoptic nucleus, and the AVP mRNA poly(A) tail length was shortened in FNDI mice compared with wild-type mice. Incubation of hypothalamic explants of wild-type mice with ER stressors caused shortening of the poly(A) tail length of AVP mRNA, accompanied by decreases in the expression. These data revealed a mechanism by which ER stress decreases poly(A) tail length of AVP mRNA, and this reduces the load of unfolded proteins that form the aggregates in ER of the AVP neurons in FNDI mice.

A novel variation in the AVP gene resulting in familial neurohypophyseal diabetes insipidus in a large Italian kindred

Familial neurohypophyseal diabetes insipidus (FNDI) is mostly an autosomal dominant inherited disorder presenting with severe polydipsia and polyuria typically in early childhood. To date, 69 different variations in the AVP gene encoding the AVP prohormone have been identified in autosomal dominant FNDI (adFNDI). In this study we present a family of seven generations, in which a novel variation in the AVP gene seems to cause adFNDI. Clinical assessment by 24 h urine collection, water deprivation test, desmopressin (dDAVP) challenge, and magnetic resonance imaging (MRI) of the posterior pituitary are presented. The diagnosis of adFNDI was confirmed by direct DNA sequence analysis of the AVP gene. Inheritance pattern and clinical history clearly pointed towards adFNDI. Inability of concentrating urine upon dehydration was demonstrated by a water deprivation test, and neurohypophyseal diabetes insipidus was strongly suspected after dDAVP administration, during which renal concentration ability quadrupled. MRI revealed a very weak pituitary "bright spot" in each of six subjects and a further reduction in the size of the neurohypophysis in a 7-year follow-up MRI scan in one subject. DNA sequence analysis revealed heterozygousity for a novel g.1785T > C gene variation predicting a p.Leu63Pro substitution in four affected subjects. Genetic testing in the diagnostic evaluation of families in which diabetes insipidus segregates is highly recommended in that interpretation of clinical assessments can be difficult. Furthermore, presymptomatic diagnosis can ease the parental concern of the carrier status of their offspring, and also avoid unnecessary surveillance of those being unaffected.

BiP mRNA expression is upregulated by dehydration in vasopressin neurons in the hypothalamus in mice

The immunoglobulin heavy chain binding protein (BiP) is an endoplasmic reticulum (ER) chaperone that facilitates the proper folding of newly synthesized secretory and transmembrane proteins. Here we report that BiP mRNA was expressed in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus in wild-type mice under basal conditions. Dual in situ hybridization in the SON and PVN demonstrated that BiP mRNA was expressed in almost all the neurons of arginine vasopressin (AVP), an antidiuretic hormone. BiP mRNA expression levels were increased in proportion to AVP mRNA expression in the SON and PVN under dehydration. These data suggest that BiP is involved in the homeostasis of ER function in the AVP neurons in the SON and PVN.