Endoplasmic reticulum-associated degradation of the mouse PC1/3-N222D hypomorph and human PCSK1 mutations contributes to obesity.

BACKGROUND: The proprotein convertase 1/3 (PC1/3), encoded by proprotein convertase subtilisin/kexin type 1 (PCSK1), cleaves and hence activates several orexigenic and anorexigenic proproteins. Congenital inactivation of PCSK1 leads to obesity in human but not in mice. However, a mouse model harboring the hypomorphic mutation N222D is obese. It is not clear why the mouse models differ in phenotype. METHODS: Gene expression analysis was performed with pancreatic islets from Pcsk1(N222D/N222D) mice. Subsequently, biosynthesis, maturation, degradation and activity were studied in islets, pituitary, hypothalamus and cell lines. Coimmunoprecipitation of PC1/3-N222D and human PC1/3 variants associated with obesity with the endoplasmic reticulum (ER) chaperone BiP was studied in cell lines. RESULTS: Gene expression analysis of islets of Pcsk1(N222D/N222D) mice showed enrichment of gene sets related to the proteasome and the unfolded protein response. Steady-state levels of PC1/3-N222D and in particular the carboxy-terminally processed form were strongly reduced in islets, pituitary and hypothalamus. However, impairment of substrate cleavage was tissue dependent. Proinsulin processing was drastically reduced, while processing of proopiomelanocortin (POMC) to adrenocorticotropic hormone (ACTH) in pituitary was only mildly impaired. Growth hormone expression and IGF-1 levels were normal, indicating near-normal processing of hypothalamic proGHRH. PC1/3-N222D binds to BiP and is rapidly degraded by the proteasome. Analysis of human PC1/3 obesity-associated mutations showed increased binding to BiP and prolonged intracellular retention for all investigated mutations, in particular for PC1/3-T175M, PC1/3-G226R and PC1/3-G593R. CONCLUSIONS: This study demonstrates that the hypomorphic mutation in Pcsk1(N222D) mice has an effect on catalytic activity in pancreatic islets, pituitary and hypothalamus. Reduced substrate processing activity in Pcsk1(N222D/N222D) mice is due to enhanced degradation in addition to reduced catalytic activity of the mutant. PC1/3-N222D binds to BiP, suggesting impaired folding and reduced stability. Enhanced BiP binding is also observed in several human obesity-associated PC1/3 variants, suggesting a common mechanism.

A nonsense loss-of-function mutation in PCSK1 contributes to dominantly inherited human obesity.

BACKGROUND: A significant proportion of severe familial forms of obesity remain genetically elusive. Taking advantage of our unique cohort of multigenerational obese families, we aimed to assess the contribution of rare mutations in 29 common obesity-associated genes to familial obesity, and to evaluate in these families the putative presence of nine known monogenic forms of obesity. METHODS: Through next-generation sequencing, we sequenced the coding regions of 34 genes involved in polygenic and/or monogenic forms of obesity in 201 participants (75 normal weight individuals, 54 overweight individuals and 72 individuals with obesity class I, II or III) from 13 French families. In vitro functional analyses were performed to investigate the mutation PCSK1-p.Arg80* which was identified in a family. RESULTS: A novel heterozygous nonsense variant in PCSK1 (p.Arg80*), encoding a propeptide truncated to less than two exons (out of 14), was found to co-segregate with obesity in a three-generation family. We demonstrated that this mutation inhibits PCSK1 enzyme activity and that this inhibition most likely does not involve a strong physical interaction. Furthermore, both mutations PCSK1-p.Asn180Ser and POMC-p.Phe144Leu, which had previously been reported to be associated with severe obesity, were also identified in this study, but did not co-segregate with obesity. Finally, we did not identify any rare mutations co-segregating with obesity in common obesity susceptibility genes, except for CADM2 and QPCTL, where we found two novel variants (p.Arg81His and p.Leu98Pro, respectively) in three obese individuals. CONCLUSIONS: We showed for the first time that a nonsense mutation in PCSK1 was likely to cause dominantly inherited human obesity, due to the inhibiting properties of the propeptide fragment encoded by the null allele. Furthermore, the present family sequencing design challenged the contribution of previously reported mutations to monogenic or at least severe obesity.

[Melioidosis]. / Melioidosis.

A 34-year-old woman presented two weeks after a visit to Burma with fever peaking up to 39 degrees C, chills, non-productive cough, headache, muscle pain, shortness of breath and a painful swelling on the left lower leg. She was treated immediately with intravenous amoxycillin-clavulanic acid. The Gram negative causative agent of melioidosis, Burkholderia (previously Pseudomonas) pseudomallei, was cultured from samples taken beforehand. The patient then received ceftazidime. She recovered. In view of the risk of relapse she was treated with amoxycillin-clavulanic acid for a further six months. Melioidosis is endemic in Southeast Asia and Northern Australia. It is rarely seen outside these areas. The clinical spectrum of the disease is wide and varies from fulminating sepsis to a subclinical disease and may affect any organ system, usually the lungs. The mortality of the septicaemic form after adequate treatment is 40%. Surviving patients have a high relapse rate (4-20%). Melioidosis can become chronic with formation of abscesses or can remain subclinical for many years, probably because the microorganism can survive within phagocytic cells with a risk of reactivation at moments of immunosuppression. The optimal treatment consists of ceftazidime intravenously for at least two weeks followed by an eradication phase consisting of oral antibiotics for at least 3 months.

Recovery of chronic hepatitis by treatment of concomitant hyperthyroidism.

A 15-year-old boy presented with biochemical and histological hepatic abnormalities consistent with chronic aggressive hepatitis and concomitant hyperthyroidism. After treatment with antithyroid therapy not only the hyperthyroidism subsided but also the hepatic function normalized. Two years later, the hyperthyroidism and liver function disorders relapsed in combination with a striking vitiligo and once again the liver function normalized after treating the hyperthyroidism. The liver biopsy sample taken in remission showed a normal picture without signs of hepatitis, fibrosis or cirrhosis. The diagnosis of a polyglandular syndrome was made, of which three types have been described. At this moment the patient fits best in type 3, which is a rather heterogenic group. Recovery of chronic hepatitis by treatment of concomitant hyperthyroidism has never been described before.

Bacterial infections and thrombocytopenia in chronic idiopathic thrombocytopenic purpura.

A bacterial infection was considered to be responsible for provoking or containing episodes of thrombocytopenia in 5 patients with chronic idiopathic thrombocytopenic purpura (ITP). In 3 patients the course of the disease was continuous and in 2 of them remission was attained after eradication of the infection. In the other 2 patients the course was intermittent and a number of relapses was provoked by the infection. The possible causal connection of chronic ITP and bacterial infections is briefly discussed.