The vasopressin precursor is not processed in the hypothalamus of Wolfram syndrome patients with diabetes insipidus: evidence for the involvement of PC2 and 7B2

Defects of WFS1-mediated peptide hormones secretion contribute to the manifestations of Wolfram syndrome

AIMS

The study aims to investigate whether WFS1 is involved in the regulation of the exportation and secretion of other peptide hormones, as well as to elucidate the precise molecular mechanisms underlying WS caused by pathogenic mutations in the WFS1 gene.

MATERIALS AND METHODS

The plasma proteome from the WS patients (n = 2, male) and WFS1-deficient mice (n = 5, male) were analyzed using liquid-chromatography tandem mass spectrometry (LC-MS/MS), while age- and gender-matched healthy individuals and wildtype (WT) mice serve as controls. WFS1-deficient mice were intraperitoneally injected with IGF1 starting from 4 weeks of age. Body weight was monitored every 2 days, fasting blood glucose and glucose tolerance test were performed on the day 30 and day 40 after injection of IGF1, respectively. BiFC (bimolecular fluorescence complementation) and Co-immunoprecipitation (IP) were used to analyze the interaction between WFS1 and peptide hormones. Confocal microscopy was employed to analyze the colocalization of IGF1 with ER and Golgi.

KEY FINDINGS

Peptide hormones are deficient in both the plasma of WS patients and WFS1-deficient mice. WFS1 binds to and mediates the secretion of these peptide hormones, suggesting that WFS1 serves as a general COPII vesicular receptor for sorting peptide hormones. Interestingly, the WFS1 pathogenic mutations significantly disrupt its interaction with these peptide hormones. Furthermore, intraperitoneal administration of IGF1 partially attenuates high blood glucose levels in WFS1-deficient male mice.

SIGNIFICANCE

This study suggests that WS is characterized by defective peptide hormone secretion and proposes administration of these deficient peptide hormones as a promising treatment regimen for WS.

Matching of the postmortem hypothalamus from patients and controls

The quality of postmortem hypothalamus research depends strongly on a thorough clinical investigation and documentation of the patient's disorder and therapies. In addition, a systematic and professional neuropathological investigation of the entire brain of both the cases and the controls is absolutely crucial. In the experience of the Netherlands Brain Bank (NBB), about 20% of the clinical neurological diagnoses, despite being made in first rate clinics, have to be revised or require extra diagnoses after a complete and thorough neuropathologic review by the NBB. The neuropathology examination may reveal for instance that the elderly "controls" already have preclinical neurodegenerative alterations. In postmortem studies, the patient and control groups must be matched for as many as possible of the known confounding factors. This is necessary to make the groups as similar as possible, except for the topic being investigated. Confounding factors are present (i) before, (ii) during, and (iii) after death. They are, respectively: (i) genetic background, systemic diseases, duration and gravity of illness, medicines and addictive compounds used, age, sex, gender identity, sexual orientation, clock- and seasonal time of death, and lateralization; (ii) agonal state, stress of dying; and (iii) postmortem delay, freezing procedures, fixation, and storage time. Agonal state is generally estimated by measuring the pH of the brain. However, there are disorders in which pH is lower as a part of the disease process. Because of the large number of potentially confounding factors that differ according to, for instance, brain area and disease, a brain bank should have a large number of controls at its disposal for appropriate matching. If matching fails for some confounders, the influence of the confounders may be determined by statistical methods, such as analysis of variance or the regression models.

Wolfram syndrome: clinical and genetic profiling of a cohort from a tertiary care centre with characterization of the primary gonadal failure

BACKGROUND

Wolfram syndrome (WFS) is a rare, monogenic neurodegenerative syndrome characterised by insulin requiring non-autoimmune diabetes mellitus (DM) and optic atrophy which are usually the earliest and commonest manifestations. However, there are other features which are under-recognized, adding to morbidity and premature mortality in these patients.

METHODS

Five patients (three males, two females) with genetically confirmed WFS at a single tertiary care centre were prospectively followed up. Their symptomatology, clinical profile, genetic analysis and radiology were analyzed. Multidisciplinary approach was used for comprehensive clinical care of this cohort. Patients with primary gonadal failure were subjected to biopsy and immunohistochemistry (IHC) for wolframin was performed.

RESULTS

DM was the earliest presenting manifestation at 6.2 ± 1.3 years followed by optic atrophy at 10.4 ± 2.3 years, diabetes insipidus at 12 ± 2.1 years and deafness at 12.8 ± 2.1 years. All patients were autoantibody negative with low C-peptide(<0.6 ng/ml). Hypoglycemic episodes were frequent (upto 60%) but there was no instance of diabetic ketoacidosis. Optic atrophy was present alongwith proliferative diabetic retinopathy and cataract in 40%. Uncommon manifestations included neuropsychiatric features, parasuicide, cystopathy, brainstem atrophy and hypergonadotropic hypogonadism only in adult males (n = 2). Testicular biopsy revealed partly hyalinised seminiferous tubules and prominence of Leydig cells. IHC confirmed the presence of mutated wolframin, which was not significantly different from normal testis specimen on protein quantification.

CONCLUSIONS

WFS requires a multidisciplinary approach with special emphasis on early diagnosis and management of other endocrine and non-endocrine features so as to improve long-term outcomes. Gonadal functions need periodic assessment, especially in adult males.

Hippocampus and Hypothalamus RNA-sequencing of WFS1-deficient Mice

Wolfram syndrome is caused by mutations in the WFS1 gene. WFS1 protein dysfunction results in a range of neuroendocrine syndromes and is mostly characterized by juvenile-onset diabetes mellitus and optic atrophy. WFS1 has been shown to participate in membrane trafficking, protein processing and Ca²⁺ homeostasis in the endoplasmic reticulum. Aim of the present study was to find the transcriptomic changes influenced by WFS1 in the hypothalamus and hippocampus using RNA-sequencing. The WFS1-deficient mice were used as a model system to analyze the changes in transcriptional networks. The number of differentially expressed genes between hypothalami of WFS1-deficient (Wfs1KO) and wild-type (WT) mice was 43 and between hippocampi 311 with False Discovery Rate (FDR) <0.05. Avpr1a and Avpr1b were significantly upregulated in the hypothalamus and hippocampus of Wfs1KO mice respectively. Trpm8 was the most upregulated gene in the hippocampus of Wfs1KO mice. The functional analysis revealed significant enrichment of networks and pathways associated with protein synthesis, cell-to-cell signaling and interaction, molecular transport, metabolic disease and nervous system development and function. In conclusion, the transcriptomic profiles of WFS1-deficient hypothalamus and hippocampus do indicate the activation of degenerative molecular pathways causing the clinical occurrences typical to Wolfram syndrome.

Knockdown of wfs1, a fly homolog of Wolfram syndrome 1, in the nervous system increases susceptibility to age- and stress-induced neuronal dysfunction and degeneration in Drosophila

Wolfram syndrome (WS), caused by loss-of-function mutations in the Wolfram syndrome 1 gene (WFS1), is characterized by juvenile-onset diabetes mellitus, bilateral optic atrophy, and a wide spectrum of neurological and psychiatric manifestations. WFS1 encodes an endoplasmic reticulum (ER)-resident transmembrane protein, and mutations in this gene lead to pancreatic β-cell death induced by high levels of ER stress. However, the mechanisms underlying neurodegeneration caused by WFS1 deficiency remain elusive. Here, we investigated the role of WFS1 in the maintenance of neuronal integrity in vivo by knocking down the expression of wfs1, the Drosophila homolog of WFS1, in the central nervous system. Neuronal knockdown of wfs1 caused age-dependent behavioral deficits and neurodegeneration in the fly brain. Knockdown of wfs1 in neurons and glial cells resulted in premature death and significantly exacerbated behavioral deficits in flies, suggesting that wfs1 has important functions in both cell types. Although wfs1 knockdown alone did not promote ER stress, it increased the susceptibility to oxidative stress-, excitotoxicity- or tauopathy-induced behavioral deficits, and neurodegeneration. The glutamate release inhibitor riluzole significantly suppressed premature death phenotypes induced by neuronal and glial knockdown of wfs1. This study highlights the protective role of wfs1 against age-associated neurodegeneration and furthers our understanding of potential disease-modifying factors that determine susceptibility and resilience to age-associated neurodegenerative diseases.

Wolfram syndrome (WS), a neurodegenerative disorder with an autosomal recessive inheritance pattern, has a variable clinical presentation that includes diabetes mellitus, optic atrophy, and a wide spectrum of neurological and psychiatric manifestations. Homozygous mutations in WFS1 are causative for WS. The prognosis of WS is poor, and most patients die prematurely with respiratory failure due to brain stem atrophy. However, the mechanisms underlying the neurological manifestations of WS remain elusive. In this study, we used the fruit fly Drosophila to examine the neurological features of WS by generating genetically modified flies harboring knockdown of wfs1, the fly homolog of WFS1, in the central nervous system. These flies developed age-dependent behavioral deficits, neurodegeneration and premature death. wfs1-deficient flies were vulnerable to various age-related stressors such as oxidative stress and excitotoxicity, and to neurodegeneration caused by Alzheimer’s disease-related toxic proteins. The premature death phenotype in wfs1-deficient flies was ameliorated by administration of riluzole, which inhibits glutamate-induced excitotoxicity. This study provides insight into the mechanisms underlying neurodegeneration not only in WS, but also in age-associated neurodegenerative diseases such as Alzheimer’s disease.

The art of matching brain tissue from patients and controls for postmortem research

The quality of postmortem research depends strongly on a thorough clinical investigation and documentation of the patient's disorder and therapies. In addition, a systematic and professional neuropathologic investigation of both cases and controls is absolutely crucial. In the experience of the Netherlands Brain Bank (NBB), about 20% of clinical neurologic diagnoses, despite being made in first-rate clinics, have to be revised or require an extra diagnosis after a complete and thorough review by the NBB. The neuropathology examination may reveal for instance that the "controls" already have preclinical neurodegenerative alterations. In postmortem studies the patient and control groups must be matched for as many of the known confounding factors as possible. This is necessary to make the groups as similar as possible, except for the topic being investigated. Confounding factors are present before, during, and after death. They are respectively: (1) genetic background, systemic diseases, duration and gravity of illness, medicines and addictive compounds used, age, sex, gender identity, sexual orientation, circadian and seasonal fluctuations, lateralization; (2) agonal state, stress of dying; and (3) postmortem delay, freezing procedures, fixation and storage time. Consequently, a brain bank should have a large number of controls at its disposal for appropriate matching. If matching fails for some confounders, then their influence may be determined by statistical methods such as analysis of variance or regression models.

Genetics of Diabetes Insipidus

Diabetes insipidus is a disease characterized by polyuria and polydipsia due to inadequate release of arginine vasopressin from the posterior pituitary gland (neurohypophyseal diabetes insipidus) or due to arginine vasopressin insensitivity by the renal distal tubule, leading to a deficiency in tubular water reabsorption (nephrogenic diabetes insipidus). This article reviews the genetics of diabetes insipidus in the context of its diagnosis, clinical presentation, and therapy.

Wfs1 is expressed in dopaminoceptive regions of the amniote brain and modulates levels of D1-like receptors

During amniote evolution, the construction of the forebrain has diverged across different lineages, and accompanying the structural changes, functional diversification of the homologous brain regions has occurred. This can be assessed by studying the expression patterns of marker genes that are relevant in particular functional circuits. In all vertebrates, the dopaminergic system is responsible for the behavioral responses to environmental stimuli. Here we show that the brain regions that receive dopaminergic input through dopamine receptor D₁ are relatively conserved, but with some important variations between three evolutionarily distant vertebrate lines–house mouse (Mus musculus), domestic chick (Gallus gallus domesticus) / common quail (Coturnix coturnix) and red-eared slider turtle (Trachemys scripta). Moreover, we find that in almost all instances, those brain regions expressing D1-like dopamine receptor genes also express Wfs1. Wfs1 has been studied primarily in the pancreas, where it regulates the endoplasmic reticulum (ER) stress response, cellular Ca²⁺ homeostasis, and insulin production and secretion. Using radioligand binding assays in wild type and Wfs1^-/- mouse brains, we show that the number of binding sites of D1-like dopamine receptors is increased in the hippocampus of the mutant mice. We propose that the functional link between Wfs1 and D1-like dopamine receptors is evolutionarily conserved and plays an important role in adjusting behavioral reactions to environmental stimuli.

Diabetes mellitus, diabetes insipidus, optic atrophy, and deafness: A case of Wolfram (DIDMOAD) syndrome

Purpose

To report a case of Wolfram syndrome (WS) characterized by diabetes mellitus, diabetes insipidus, progressive optic atrophy, and deafness.

Case report

A 19-year-old female patient, a known case of diabetes mellitus type I from six years before, presented with progressive vision loss since four years earlier. On fundoscopic examination, she had bilateral optic atrophy without diabetic retinopathy. The patient also had diabetes insipidus, neurosensory deafness, and neurogenic bladder.

Conclusion

WS should be considered a differential diagnosis in patients with diabetes mellitus who present with optic atrophy, and it is necessary to perform a hearing test as well as collecting 24-h urine output.

Prohormone convertase 2 activity is increased in the hippocampus of Wfs1 knockout mice

Background: Mutations in WFS1 gene cause Wolfram syndrome, which is a rare autosomal recessive disorder, characterized by diabetes insipidus, diabetes mellitus, optic nerve atrophy, and deafness. The WFS1 gene product wolframin is located in the endoplasmic reticulum. Mice lacking this gene exhibit disturbances in the processing and secretion of peptides, such as vasopressin and insulin. In the brain, high levels of the wolframin protein have been observed in the hippocampus, amygdala, and limbic structures. The aim of this study was to investigate the effect of Wfs1 knockout (KO) on peptide processing in mouse hippocampus. A peptidomic approach was used to characterize individual peptides in the hippocampus of wild-type and Wfs1 KO mice.

Results: We identified 126 peptides in hippocampal extracts and the levels of 10 peptides differed between Wfs1 KO and wild-type mice at P < 0.05. The peptide with the largest alteration was little-LEN, which level was 25 times higher in the hippocampus of Wfs1 KO mice compared to wild-type mice. Processing (cleavage) of little-LEN from the Pcsk1n gene product proSAAS involves prohormone convertase 2 (PC2). Thus, PC2 activity was measured in extracts prepared from the hippocampus of Wfs1 KO mice. The activity of PC2 in Wfs1 mutant mice was significantly higher (149.9 ± 2.3%, p < 0.0001, n = 8) than in wild-type mice (100.0 ± 7.0%, n = 8). However, Western blot analysis showed that protein levels of 7B2, proPC2 and PC2 were same in both groups, and so were gene expression levels.

Conclusion: Processing of proSAAS is altered in the hippocampus of Wfs1-KO mice, which is caused by increased activity of PC2. Increased activity of PC2 in Wfs1 KO mice is not caused by alteration in the levels of PC2 protein. Our results suggest a functional link between Wfs1 and PC2. Thus, the detailed molecular mechanism of the role of Wfs1 in the regulation of PC2 activity needs further investigation.

Congenital central diabetes insipidus and optic atrophy in a Wolfram newborn: is there a role for WFS1 gene in neurodevelopment?

Background

Wolfram syndrome (WS) is an autosomal recessive neurodegenerative disorder characterized by diabetes mellitus (DM), optic atrophy (OA), central diabetes insipidus (CDI) and deafness (D).

The phenotype of the disease has been associated with several mutations in the WFS1 gene, a nuclear gene localized on chromosome 4. Since the discovery of the association between WFS1 gene and Wolfram syndrome, more than 150 mutations have been identified in WS patients.

We previously described the first case of perinatal onset of Wolfram syndrome newborn carrying a segmental uniparental heterodysomy affecting the short arm of chromosome 4 responsible for a significant reduction in wolframin expression.

Here we review and discuss the pathophysiological mechanisms that we believe responsible for the perinatal onset of Wolfram syndrome as these data strongly suggest a role for WFS1 gene in foetal and neonatal neurodevelopment.

Case presentation

We described a male patient of 30 weeks’ gestation with intrauterine growth restriction and poly-hydramnios.

During the first days of life, the patient showed a 19% weight loss associated with polyuria and hypernatremia. The presence of persistent hypernatremia (serum sodium 150 mEq/L), high plasma osmolarity (322 mOsm/L) and low urine osmolarity (190 mOsm/l) with a Uosm/Posm ratio < 1 were consistent with CDI. The diagnosis of CDI was confirmed by the desmopressin test and the brain magnetic resonance imaging (MRI) at 34 weeks of age, that showed the lack of posterior pituitary hyperintense signal. In addition, a bilateral asymmetrical optic nerve hypoplasia associated with right orbital bone hypoplasia was observed, suggesting the diagnosis of WF.

During the five years follow-up the patient did not developed glucose intolerance or diabetes mellitus. By the end of the second year of life, primary non-autoimmune central hypothyroidism and mild neurodevelopment retardation were diagnosed.

Conclusions

The analysis of our case, in the light of the most recent literature, suggests a possible role for WFS1 gene in the development of certain brain structures during the fetal period.

Wolfram syndrome should be considered in the differential diagnosis of the rare cases of congenital central diabetes insipidus developed in the neonatal period.

Silencing of the WFS1 gene in HEK cells induces pathways related to neurodegeneration and mitochondrial damage

The gene WFS1 encodes a protein with unknown function although its functional deficiency causes different neuropsychiatric and neuroendocrine syndromes. In the present study, we aimed to find the functional networks influenced by the time-dependent silencing of WFS1 in HEK cells. We performed whole genome gene expression profiling (Human Gene 1.0 ST Arrays) in HEK cells 24, 48, 72, and 96 h after transfection with three different WFS1 siRNAs. To verify silencing we performed quantitative RT-PCR and Western blot analysis. Analysis was conducted in two ways. First we analyzed the overall effect of the siRNA treatment on the gene expression profile. As a next step we performed time-course analysis separately for different siRNAs and combined for all siRNAs. Quantitative RT-PCR and Western blot analysis confirmed clear silencing of the expression of WFS1 after 48 h. Significant (FDR value<10%) changes in the expression of 11 genes was identified with most of these genes being related to the mitochondrial dysfunction and apoptosis. Time-course analysis confirmed significant correlations between WFS1 silencing and changes in the expression profiles of several genes. The pathways that were influenced significantly by WFS1 silencing were related to mitochondrial damage and neurodegenerative diseases. Our findings suggest a role of WFS1 gene in cell survival and its involvement in degenerative diseases.

Wolfram syndrome 1 and Wolfram syndrome 2

PURPOSE OF REVIEW

Wolfram syndrome 1 (WS1) is an autosomal recessive disorder characterized by diabetes insipidus, diabetes mellitus, optic atrophy, and deafness (DI DM OA D syndrome) associated with other variable clinical manifestations. The causative gene for WS1 (WFS1) encoding wolframin maps to chromosome 4p16.1. Wolframin has an important function in maintaining the homeostasis of the endoplasmic reticulum (ER) in pancreatic β cells. Recently, another causative gene, CISD2, has been identified in patients with a type of Wolfram syndrome (WS2) resulting in early optic atrophy, diabetes mellitus, deafness, decreased lifespan, but not diabetes insipidus. The CISD2-encoded protein ERIS (endoplasmic reticulum intermembrane small protein) also localizes to ER, but does not interact directly with wolframin. ERIS maps to chromosome 4q22.

RECENT FINDINGS

Numerous studies have shown an interesting similarity between WFS1 and CISD2 genes. Experimental studies demonstrated that the Cisd2 knockout (Cisd2) mouse shows premature aging and typical symptoms of Wolfram syndrome. These researches provide interesting insight into the relation of neurodegenerative diseases, mitochondrial disorders, and autophagy and are useful for the pathophysiological understanding of both Wolfram syndrome and mitochondrial-mediated premature aging.

SUMMARY

The knowledge of WS1 and WS2 pathogenesis, and of the interactions between WFS1 and CISD2 genes, is useful for accurate diagnostic classification and for diagnosis of presymptomatic individuals.

Hypothalamic gene expression profile indicates a reduction in G protein signaling in the Wfs1 mutant mice

The Wfs1 gene codes for a protein with unknown function, but deficiency in this protein results in a range of neuropsychiatric and neuroendocrine syndromes. In the present study we aimed to find the functional networks influenced by Wfs1 in the hypothalamus. We performed gene expression profiling (Mouse Gene 1.0 ST Arrays) in Wfs1-deficient mice; 305 genes were differentially expressed with nominal P value<0.01. FDR (false discovery rate)-adjusted P values were significant (0.007) only for two genes: C4b (t=9.66) and Wfs1 (t=-9.03). However, several genes related to G protein signaling were very close to the FDR-adjusted significance level, such as Rgs4 (regulator of G protein signaling 4) that was downregulated (-0.34, t=-5.4) in Wfs1-deficient mice. Changes in Rgs4 and C4b expression were confirmed by QRT-PCR. In humans, Rgs4 is in the locus for bipolar disease (BPD), and its expression is downregulated in BPD. C4b is a gene related to the neurodegenerative diseases. Functional analysis including the entire data set revealed significant alterations in the canonical pathway "G protein-coupled receptor signaling." The gene expression profile in the hypothalami of the Wfs1 mutant mice was significantly similar to the profiles of following biological functions: psychological disorders, bipolar disorder, mood disorder. In conclusion, hypothalamic gene expression profile resembles with some molecular pathways functionally related to the clinical syndromes in the Wolfram syndrome patients.

Endocrine and metabolic aspects of the Wolfram syndrome

Wolfram syndrome (WS), also known as DIDMOAD (Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness), is a neurodegenerative disease with autosomal recessive inheritance with incomplete penetrance. DIDMOAD is a very rare disease with an estimated prevalence of 1 in 770,000 and it is believed to occur in 1 of 150 patients with juvenile-onset insulin-dependent diabetes mellitus. Additionally, WS may also present with different endocrine and metabolic abnormalities such as anterior and posterior pituitary gland dysfunction. This mini-review summarizes the variable presentation of WS and the need of screening for other metabolic and hormonal abnormalities, coexisting in this rare syndrome.

Familial forms of diabetes insipidus: clinical and molecular characteristics

Over the past two decades, the genetic and molecular basis of familial forms of diabetes insipidus has been elucidated. Diabetes insipidus is a clinical syndrome characterized by the excretion of abnormally large volumes of diluted urine (polyuria) and increased fluid intake (polydipsia). The most common type of diabetes insipidus is caused by lack of the antidiuretic hormone arginine vasopressin (vasopressin), which is produced in the hypothalamus and secreted by the neurohypophysis. This type of diabetes insipidus is referred to here as neurohypophyseal diabetes insipidus. The syndrome can also result from resistance to the antidiuretic effects of vasopressin on the kidney, either at the level of the vasopressin 2 receptor or the aquaporin 2 water channel (which mediates the re-absorption of water from urine), and is referred to as renal or nephrogenic diabetes insipidus. Differentiation between these two types of diabetes insipidus and primary polydipsia can be difficult owing to the existence of partial as well as complete forms of vasopressin deficiency or resistance. Seven different familial forms of diabetes insipidus are known to exist. The clinical presentation, genetic basis and cellular mechanisms responsible for them vary considerably. This information has led to improved methods of differential diagnosis and could provide the basis of new forms of therapy.

Wolfram syndrome and WFS1 gene

Wolfram syndrome (WS) (MIM 222300) is a rare multisystem neurodegenerative disorder of autosomal recessive inheritance, also known as DIDMOAD (diabetes insipidus, insulin-deficient diabetes mellitus, optic atrophy and deafness). A Wolfram gene (WFS1) has been mapped to chromosome 4p16.1 which encodes an endoplasmic reticulum (ER) membrane-embedded protein. ER localization suggests that WFS1 protein has physiological functions in membrane trafficking, secretion, processing and/or regulation of ER calcium omeostasis. Disturbances or overloading of these functions induce ER stress responses, including apoptosis. Most WS patients carry mutations in this gene, but some studies provided evidence for genetic heterogeneity, and the genotype-phenotype relationships are not clear. Here we review the data regarding the mechanisms and the mutations of WFS1 gene that relate to WS.

Pax6 regulates the proglucagon processing enzyme PC2 and its chaperone 7B2

Pax6 is important in the development of the pancreas and was previously shown to regulate pancreatic endocrine differentiation, as well as the insulin, glucagon, and somatostatin genes. Prohormone convertase 2 (PC2) is the main processing enzyme in pancreatic alpha cells, where it processes proglucagon to produce glucagon under the spatial and temporal control of 7B2, which functions as a molecular chaperone. To investigate the role of Pax6 in glucagon biosynthesis, we studied potential target genes in InR1G9 alpha cells transfected with Pax6 small interfering RNA and in InR1G9 clones expressing a dominant-negative form of Pax6. We now report that Pax6 controls the expression of the PC2 and 7B2 genes. By binding and transactivation studies, we found that Pax6 indirectly regulates PC2 gene transcription through cMaf and Beta2/NeuroD1 while it activates the 7B2 gene both directly and indirectly through the same transcription factors, cMaf and Beta2/NeuroD1. We conclude that Pax6 is critical for glucagon biosynthesis and processing by directly and indirectly activating the glucagon gene through cMaf and Beta2/NeuroD1, as well as the PC2 and 7B2 genes.

Distribution of Wfs1 protein in the central nervous system of the mouse and its relation to clinical symptoms of the Wolfram syndrome

Mutations in the coding region of the WFS1 gene cause Wolfram syndrome, a rare multisystem neurodegenerative disorder of autosomal recessive inheritance. Patients with Wolfram syndrome display considerable clinical pleiomorphism, and symptoms such as neurological complications and psychiatric disorders are common. In the present study we have characterized Wfs1 expression pattern in the mouse central nervous system by using a combination of immunohistochemistry on wild-type mice and X-Gal staining of Wfs1 knockout mice with targeted insertion of the lacZ reporter. We identified a robust enrichment of Wfs1 protein in the central extended amygdala and ventral striatum. Prominent Wfs1 expression was seen in the hippocampal CA1 region, parasubiculum, superficial part of the second and third layers of the prefrontal cortex and proisocortical areas, hypothalamic magnocellular neurosecretory system, and central auditory pathway. Wfs1 expression was also detected in numerous brainstem nuclei and in laminae VIII and IX of the spinal cord. Wfs1-positive nerve fibers were found in the medial forebrain bundle, reticular part of the substantia nigra, globus pallidus, posterior caudate putamen, lateral lemniscus, alveus, fimbria, dorsal hippocampal commissure, subiculum, and to a lesser extent in the central sublenticular extended amygdala, compact part of substantia nigra, and ventral tegmental area. The neuroanatomical findings suggest that the lack of Wfs1 protein function can be related to several neurological and psychiatric symptoms found in Wolfram syndrome. Enrichment of Wfs1 protein in the central extended amygdala suggests a role in the modulation of anxiety and fear.

Pituitary abnormalities in Prader–Willi syndrome and early onset morbid obesity

Prader-Willi syndrome (PWS) is a well-defined syndrome of childhood-obesity which can serve as a model for investigating early onset childhood obesity. Many of the clinical features of PWS (e.g., hyperphagia, hypogonadotropic hypogonadism, growth hormone deficiency) are hypothesized to be due to abnormalities of the hypothalamus and/or pituitary gland. Children who become severely obese very early in life (i.e., before age 4 years) may also have a genetic etiology of their obesity, perhaps with associated neuroendocrine and hypothalamo-pituitary defects, as infants and very young children have limited access to environmental factors that contribute to obesity. We hypothesized that morphologic abnormalities of the pituitary gland would be seen in both individuals with PWS and other subjects with early onset morbid obesity (EMO). This case-control study included individuals with PWS (n = 27, age 3 months to 39 years), patients with EMO of unknown etiology (n = 16, age 4-22 years; defined as body mass index greater than the 97th centile for age before age 4 years), and normal weight siblings (n = 25, age 7 months to 43 years) from both groups. Participants had 3-dimensional magnetic resonance imaging to evaluate the pituitary gland, a complete history and physical examination, and measurement of basal pituitary hormones. Subjects with PWS and EMO had a higher prevalence of pituitary morphological abnormalities than did control subjects (74% PWS, 69% EMO, 8% controls; P < 0.001). Anterior pituitary hormone deficiencies were universal in individuals with PWS (low IGF-1 in 100%, P < 0.001 PWS vs. controls; central hypothyroidism in 19%, P = 0.052, and hypoplastic genitalia or hypogonadotropic hypogonadism in 100%, P < 0.001), and was often seen in individuals with EMO (6%, P = 0.89 vs. control, 31%, P = 0.002, and 25%, P = 0.018, respectively). The presence of a hypoplastic pituitary gland appeared to correlate with the presence of anterior pituitary hormone deficiencies in individuals with EMO, but no correlation was apparent in individuals with PWS. In conclusion, the high frequency of both morphological and hormonal abnormalities of the pituitary gland in both individuals with PWS and EMO suggests that abnormalities in the hypothalamo-pituitary axis are features not only of PWS, but also frequently of EMO of unknown etiology.

Sodium-potassium ATPase 1 subunit is a molecular partner of Wolframin, an endoplasmic reticulum protein involved in ER stress

Wolfram syndrome, an autosomal recessive disorder characterized by diabetes mellitus and optic atrophy, is caused by mutations in the WFS1 gene encoding an endoplasmic reticulum (ER) membrane protein, Wolframin. Although its precise functions are unknown, Wolframin deficiency increases ER stress, impairs cell cycle progression and affects calcium homeostasis. To gain further insight into its function and identify molecular partners, we used the WFS1-C-terminal domain as bait in a yeast two-hybrid screen with a human brain cDNA library. Na+/K+ ATPase beta1 subunit was identified as an interacting clone. We mapped the interaction to the WFS1 C-terminal and transmembrane domains, but not the N-terminal domain. Our mapping data suggest that the interaction most likely occurs in the ER. We confirmed the interaction by co-immunoprecipitation in mammalian cells and with endogenous proteins in JEG3 placental cells, neuroblastoma SKNAS and pancreatic MIN6 beta cells. Na+/K+ ATPase beta1 subunit expression was reduced in plasma membrane fractions of human WFS1 mutant fibroblasts and WFS1 knockdown MIN6 pancreatic beta-cells compared with wild-type cells; Na+/K+ ATPase alpha1 subunit expression was also reduced in WFS-depleted MIN6 beta cells. Induction of ER stress in wild-type cells only partly accounted for the reduced Na+/K+ ATPase beta1 subunit expression observed. We conclude that the interaction may be important for Na+/K+ ATPase beta1 subunit maturation; loss of this interaction may contribute to the pathology seen in Wolfram syndrome via reductions in sodium pump alpha1 and beta1 subunit expression in pancreatic beta-cells.

Mitochondrial diabetes, DIDMOAD and other inherited diabetes syndromes

Inherited diabetes syndromes are individually rare but collectively make up a significant proportion of patients attending diabetes clinics, some of whom have multiple handicaps. This chapter focuses on syndromes in which major advances have been made in our understanding of the underlying molecular genetics. These conditions demonstrate novel genetic mechanisms such as maternal inheritance and genetic imprinting. They are also fascinating as they aid our understanding of insulin metabolism, both normal and abnormal. As the causative genes are identified, future issues will be the availability of genetic testing, their contribution to the genetic heterogeneity of the more common types of diabetes, and functional studies of the relevant proteins. It is probable that other subtypes of diabetes will be identified as the relevant metabolic pathways are characterized. This is an exciting time to be a diabetes physician as diabetology returns to being a diagnostic rather than a mainly management-based speciality.

WFS1/wolframin mutations, Wolfram syndrome, and associated diseases

Wolfram syndrome (WS) is the inherited association of juvenile-onset insulin-dependant diabetes mellitus and progressive bilateral optic atrophy. A nuclear gene, WFS1/wolframin, was identified that segregated with disease status and demonstrated an autosomal recessive mode of inheritance. Mutation analysis of the WFS1 gene in WS patients has identified mutations in 90% of patients. Most were compound heterozygotes with private mutations distributed throughout the gene with no obvious hotspots. The private nature of the mutations in WS patients and the low frequencies make it difficult to determine the biological or clinical relevance of these mutations. Mutation screening in patients with psychiatric disorders or diabetes mellitus has also been performed to test the hypothesis that heterozygous carriers of WFS1 gene mutations are at an increased risk following the observation that WS first-degree relatives have a higher frequency of these disorders. Most studies showed no association, however two missense mutations were identified that demonstrated significant association with psychiatric disorders and diabetes mellitus. Population association studies and functional studies of these variants will need to be performed to confirm these preliminary results. The elucidation of functions and functional pathways for the WFS1 gene product and variants will shed light on the effect of such disparate mutations on gene function and their role in the resulting clinical phenotype in WS and associated disorders.

Excitatory peptides and osmotic pressure modulate mechanosensitive cation channels in concert

Behavioral and neuroendocrine responses underlying systemic osmoregulation are synergistically controlled by osmoreceptors and neuropeptides released within the hypothalamus. Although mechanisms underlying osmoreception are understood, the cellular basis for the integration of osmotic and peptidergic signals remains unknown. Here we show that the excitatory effects of angiotensin II, cholecystokinin and neurotensin on supraoptic neurosecretory neurons are due to the stimulation of the stretch-inactivated cation channels responsible for osmoreception. This molecular convergence underlies the facilitatory effects of neuropeptides on responses to osmotic stimulation and provides a basis for the gating effects of plasma osmolality on the responsiveness of osmoregulatory neurons to peptidergic stimulation.

The human hypothalamo-neurohypophysial system in health and disease

The present paper reviews the changes observed in the human supraoptic (SON) and paraventricular (PVN) nuclei, and their projections to the neurohypophysis, median eminence and to other brain areas in health and disease.