Mutations in the human melanocortin-4 receptor gene associated with severe familial obesity disrupts receptor function through multiple molecular mechanisms

Mutations in the melanocortin-4 receptor gene (MC4R) represent the commonest monogenic cause of human obesity. However, information regarding the precise effects of such mutations on receptor function is very limited. We examined the functional properties of 12 different mutations in human MC4R that result in severe, familial, early-onset obesity. Of the nine missense mutants studied, four were completely unable to generate cAMP in response to ligand and five were partially impaired. Four showed evidence of impaired cell surface expression and six of reduced binding affinity for ligand. One mutation in the C-terminal tail, I316S, showed reduced affinity for alpha-MSH but retained normal affinity for the antagonist AgRP. None of the mutations inhibited signaling through co-transfected wild-type receptors. Thus, in the most comprehensive study to date of the functional properties of naturally occurring MC4R mutations we have (1) established that defective expression on the cell surface is a common mechanism impairing receptor function, (2) identified mutations which specifically affect ligand binding affinity thus aiding the definition of receptor structure-function relationships, (3) provided evidence against the notion that these receptor mutants act as dominant-negatives, and (4) identified a potentially novel molecular mechanism of receptor dysfunction whereby a mutation alters the relative affinities of a receptor for its natural agonist versus antagonist.     

The role of beta-catenin, TGF beta 3, NGF2, FGF2, IGFR2, and BMP4 in the pathogenesis of mesenteric sclerosis and angiopathy in midgut carcinoids

A subset of midgut carcinoids (MCs) result in mesenteric angiopathy (MA) and bowel infarction as a consequence of vascular compression caused by extensive mesenteric sclerosis (MS). The goal of this study was to determine whether the level of expression of several fibrosing-related growth factors was related to the finding of MA and/or MS in MCs. Eighteen cases of MC, 6 with both extensive MS and MA (group I), 5 with extensive MS only (group II), and 7 with ordinary MS only (group III), were analyzed for immunoexpression of beta-catenin, transforming growth factor-beta 2 (TGF beta 2), nerve growth factor 2 (NGF2), fibroblast growth factor 2 (FGF2), insulin growth factor receptor (IGFR), and bone morphogenic protein 4 (BMP4) in formalin-fixed, paraffin-embedded sections. Standard immunohistochemical technique was used following antigen retrieval. Immunostaining was scored semiquantitively as the product of the percentage and intensity (0 to 2+) of the immunostaining, giving a possible range of 0 to 200. One-way analysis of variance and Mann-Whitney nonparametric analyses were used for statistical analysis. The mean scores of immunoreactivity of each factor in groups I, II, and III were as follows: 135, 174, and 147 for beta-catenin (cytoplasmic reactivity only); 106, 112, and 92 for TGF beta 3; 1.67, 32, and 36 for NGF-2; 2.5, 48, and 55 for FGF-2; 19, 112, and 66 for IGFR2; 140, 45, and 52 for BMP4. There were significant differences in NGF-2 immunoreactivity between groups I and III (P = 0.0023) and in BMP4 immunoreactivity between groups I and II (P = 0.017) and groups I and III (P = 0.022). All MCs expressed high levels of membranous beta-catenin, moderate levels of TGF beta 3 and IGFR2, and low levels of FGF-2, with no significant differences seen among the groups. MCs with prominent MS and MA (group I) expressed significantly higher BMP4 than those in groups II and III, suggesting a potential role of BMP4 in the pathogenesis of MA. The level of NGF-2 expression was significantly lower in group I than in group III, possibly indicating abnormal angiogenesis in the formation of angiopathy.     

Activation of mucosal Vβ3+ T cells and tissue damage in human small intestine by the bacterial superantigen,Staphylococcus aureus enterotoxin B

Staphylococcus aureus enterotoxin B (SEB) was added to explants of fetal human intestine in organ culture or administered into the lumen of fetal small intestine prior to culture. Both routes produced a massive increase in lamina propria T cells expressing Vβ33, and to a lesser extent, those expressing Vβ5 and Vβ12. SEB-activated lamina propria T cells produced interleukin-2 and interferon-Y and T cell activation was accompanied by tissue damage, which was inhibited by FK506.     

Changes in bone turnover during tibolone treatment

OBJECTIVES: An open study was carried out to evaluate changes in bone remodeling markers such as N-telopeptide (NTx), tartrate-resistant acid phosphatase (TRAP), total alkaline phosphatase (TAP), and bone alkaline phosphatase (BAP) during a 1-year continuous tibolone treatment in postmenopausal women. MATERIAL AND METHODS: Thirty-six postmenopausal women were recruited for receiving tibolone 2.5 mg per day for 1 year. Densitometry and determination of biochemical markers of bone metabolism in serum and urine were performed at 1, 3, 6, and 12 months. RESULTS: Comparing baseline with 12 month's values, BAP and all resorption markers decreased significantly. NTx began to decrease since the initiation of the treatment (baseline: 74.4 +/- 5.3; 1 month: 57.5 +/- 4.2; 12 months: 36.6 +/- 2.8). BAP increased at the first month (baseline: 37.3 +/- 2.1; 1 month: 42.6 +/- 3.0) but diminished in the following months (12 months: 23.1 +/- 1.5). TAP started to decrease significantly only after 6 months of treatment (baseline: 37.3 +/- 2.1; 12 months: 31.4 +/- 2.3) and TRAP after 3 months (baseline: 9.8 +/- 0.4; 6 months: 9.1 +/- 0.5; 12 months: 8.2 +/- 0.4). Normal bone mineral density at distal and ultradistal forearm was maintained during the 1-year treatment (baseline: 0.42 +/- 0.01; 12 months: 0.42 +/- 0.01 and baseline: 0.33 +/- 0.01; 12 months: 0.33 +/- 0.01, respectively). CONCLUSION: The use of tibolone 2.5 mg per day diminished progressively and significantly bone resorption and formation markers during 1-year treatment period.     

Activity-dependent control of bulk endocytosis by protein dephosphorylation in central nerve terminals

Bulk endocytosis is the process by which nerve terminals retrieve large amounts of synaptic vesicle membrane during periods of strong stimulation intensity. The process is rapidly activated and is most probably calcium dependent in a similar manner to synaptic vesicle exocytosis. This article briefly summarizes the current knowledge of bulk endocytosis with respect to its activation, kinetics and molecular mechanism. It also presents recent data from our laboratory showing that the dephosphorylation of a group of endocytosis proteins called the dephosphins by the Ca²⁺-dependent protein phosphatase calcineurin is key to the activity-dependent stimulation of the process. Possible downstream effectors of calcineurin are discussed such as the large GTPase dynamin I and its phosphorylation-dependent interaction partner syndapin I.     

Effect of Down syndrome on the dimensions of dental crowns and tissues

Abnormal growth in Down syndrome (DS) is reflected by variable reduction in size and simplification in form of many physical traits. This study aimed to compare the thickness of enamel and dentine in deciduous and permanent mandibular incisor teeth between DS and non‐DS individuals and to clarify how these tissues contribute to altered tooth size in DS. Sample groups comprised 61 mandibular incisors (29 permanent and 32 deciduous) from DS individuals and 55 mandibular incisors (29 permanent and 26 deciduous) from non‐DS individuals. Maximum mesiodistal and labiolingual crown dimensions were measured initially, then the crowns were sectioned midsagittally and photographed using a stereomicroscope. Linear measurements of enamel and dentine thickness were obtained on the labial and lingual surfaces of the crowns, together with enamel and dentine–pulp areas and lengths of the dentino‐enamel junction. Reduced permanent crown size in DS was associated with a reduction in both enamel and dentine thickness. After adjustments were made for tooth size, DS permanent incisors had significantly thinner enamel than non‐DS permanent teeth. The DS permanent teeth also exhibited significant differences in shape and greater variability in dimensions than the non‐DS permanent teeth. Crown dimensions of deciduous incisors were similar in size or larger in DS compared with non‐DS deciduous teeth. Enamel and dentine thicknesses of the deciduous teeth were similar in DS and non‐DS individuals. The findings indicate that growth retardation in DS reduces both enamel and dentine deposition in the permanent incisors but not in the earlier‐forming deciduous predecessors. The results are also consistent with the concept of amplified developmental instability for dental traits in DS. Am. J. Hum. Biol. 13:690–698, 2001. © 2001 Wiley‐Liss, Inc.     

Retrospective evidence that the MHC (B haplotype) of chickens influences genetic resistance to attenuated infectious bronchitis vaccine strains in chickens.

Infectious bronchitis is a respiratory disease of chickens that is caused by the coronavirus infectious bronchitis virus (IBV). Virtually all broiler and layer breeder flocks are routinely vaccinated against IBV. Two hatches of 1-day-old chicks from four lines were mistakenly vaccinated for infectious bronchitis using a moderately attenuated vaccine designed for chicks of an older age. The vaccination resulted in high mortality, and chicks from three of four lines died with signs typical of infectious bronchitis. The mortality that occurred using this less-attenuated vaccine was significantly influenced by the genetic line, and the MHC (B) haplotype in chickens of three B congenic lines. B congenic chickens possessing the B*15 haplotype were resistant in contrast to chickens possessing the B*13 or B*21 haplotypes. Chicks from two further hatches of the four lines were vaccinated appropriately with a more attenuated IBV vaccine, and only limited chick mortality was seen. These retrospective data from two repeated hatches confirm earlier data indicating chicken genes influence resistance to IBV, and indicate for the first time that genes tightly linked to the B haplotype are relevant in resistance to IBV. Due to extenuating circumstances it was not possible to verify results with chicks from F2 matings. Factors that may enhance definition of the role of the B haplotype in immune response to IBV, and the desirability for further analysis of a B haplotype-linked influence on immunity to IBV are discussed.