Loss-of-Function ENPP1 Mutations Cause Both Generalized Arterial Calcification of Infancy and Autosomal-Recessive Hypophosphatemic Rickets

The analysis of rare genetic disorders affecting phosphate homeostasis led to the identification of several proteins that are essential for the renal regulation of phosphate homeostasis; for example, fibroblast growth factor 23 (FGF23), which inhibits renal phosphate reabsorption and 1,25-dihydroxyvitamin D synthesis. Here, we report presumable loss-of-function mutations in the ENPP1 gene (ectonucleotide pyrophosphatase/phosphodiesterase) in members of four families affected with hypophosphatemic rickets. We provide evidence for the conclusion that ENPP1 is the fourth gene—in addition to PHEX, FGF23, and DMP1—that, if mutated, causes hypophosphatemic rickets resulting from elevated FGF23 levels. Surprisingly, ENPP1 loss-of-function mutations have previously been described in generalized arterial calcification of infancy, suggesting an as yet elusive mechanism that balances arterial calcification with bone mineralization.     

Molecular mimicry and horror autotoxicus: do chlamydial infections elicit autoimmunity?

All species of the order Chlamydiales are obligate intracellular eubacterial pathogens of their various hosts. Two chlamydial species, Chlamydia trachomatis and Chlamydia pneumoniae, are primarily human pathogens, and each is known to cause important diseases. Some strains of C. trachomatis are sexually transmitted and frequently cause severe reproductive problems, primarily in women. Other strains of the organism serve as the aetiological agents for blinding trachoma, still the leading cause of preventable blindness in underdeveloped nations. C. pneumoniae is a respiratory pathogen known to cause community-acquired pneumonia. Importantly, both organisms engender an immunopathogenic response in the human host, and both have been associated with widely diverse, relatively common and currently idiopathic chronic diseases, most of which include an important autoimmune component. In this article, we explore the available experimental data regarding the possible elicitation of autoimmunity in various contexts by chlamydial infection, and we suggest several avenues for research to explore this potentially important issue further.     

Isolation and characterization of new exon 11-associated N-terminal splice variants of the human mu opioid receptor gene

Alternative splicing of the mu opioid receptor genes to create multiple mu receptor subtypes has been demonstrated in animals and humans. Previously, we identified a number of C-terminal variants in mice, rats and human, followed by several N-terminal variants associated with a new upstream exon in mice (exon 11). Behavioral studies in exon 11 knockout mice suggest an important role for the exon 11 variants in the analgesic actions of heroin and morphine-6β-glucuronide, but not morphine or methadone. We now have identified a homologous human exon 11 and three similar human exon 11-associated variants, suggesting conservation of exon 11 and its associated variants across species. hMOR-1i has an additional 93 amino acids at the tip of the N-terminus but is otherwise identical to hMOR-1. When expressed in Chinese hamster ovary cells, the additional 93 amino acids in hMOR-1i had little effect on opioid binding, but significantly altered agonist-induced G-protein activation. hMOR-1G1 and hMOR-1G2 predicted six transmembrane domain variants, similar to those seen in mice. The regional expression of these exon 11-associated variants, as determined by RT-PCR, varied markedly, implying region-specific alternative splicing. The presence of exon 11-associated variants in humans raises questions regarding their potential role in heroin and morphine-6β-glucuronide actions in people as they do in mice.     

How do fish ectoparasites Argulus spp. (Crustacea: Branchiura) match with their hosts at the behavioural and ecological scales?

Features of the Argulus foliaceus and A. coregoni life cycles including spatial distribution and hatching patterns of the resting eggs as well as their host searching behaviour were analyzed on the basis of field and experimental data obtained in lakes and a fish farm in the Central Finland. Published data on behaviour and ecology of these parasites were also used. The main point of this analysis was an ecological adjustment of the life cycles of parasites to that of their fish hosts at different spatial and temporal scales. Due to different spatial distribution of overwintering eggs, the newly hatched larvae of A. coregoni are more likely to attach to salmonids, which are their main hosts, while A. foliaceus to percids and cyprinids. The main peak of argulid hatching occurs in late spring-early summer and coincides with the period when most of freshwater fishes concentrate close to the shore, either for spawning, or, foraging. Nevertheless, despite the general coincidence, the parasite-host encounter rate could still be very low. The main peak of hatching is followed by a long "tail". We suggest that under fluctuating and uncertain environmental conditions characterised by both abiotic stochasticity and poor predictability of the hosts, an optimal recruitment strategy is to hedge a bet, with a proportion of eggs synchronously hatching and a proportion remaining dormant and hatching at much lower rate during an extended period. One of the main behavioural adaptations to match with the hosts is all-over-the-day searching activity of argulids. The boreal A. coregoni relies primarily on vision, which is most effective in transparent waters during long polar days in summer. Vision is also important in the behavioural repertoire of the temperate A. foliaceus in the light, but olfaction and mechanoreception in the dark provide the highest host searching rate. The two generally sympatric species of argulids segregated on the finer habitat scale. Partially overlapping on salmonid hosts, they prefer ecologically distinct categories of fish, and use different microhabitats for egg laying and searching for hosts.     

Modeling the influence of superoxide dismutase on superoxide and nitric oxide interactions,including reversible inhibition of oxygen consumption

A mathematical mass transport model was constructed in cylindrical geometry to follow coupled biochemical reactions and diffusion of oxygen, nitric oxide, superoxide, peroxynitrite, hydrogen peroxide, nitrite, and nitrate around a blood vessel. Computer simulations were performed for a 50 microm internal diameter arteriole to characterize mass transport in five concentric regions (blood, plasma layer, endothelium, vascular wall, perivascular tissue). Steady state gradients in nitric oxide, oxygen partial pressure, superoxide, and peroxynitrite, and associated production of hydrogen peroxide, nitrite, and nitrate were predicted for varying superoxide production rates, superoxide dismutase concentrations, and other physiological conditions. The model quantifies how competition between superoxide scavenging by nitric oxide and superoxide dismutase catalyzed removal varies spatially. Reversible inhibition of oxygen consumption by nitric oxide, which causes increased tissue oxygenation at deeper locations, was also included in the model. The mass transport model provides insight into complex interactions between reactive oxygen and nitrogen species in blood and tissue, and provides an objective way to evaluate the relative influence of different biochemical pathways on these interactions.     

Nicastrin is a resident lysosomal membrane protein

Nicastrin has been recently identified as part of the gamma-secretase complex that includes presenilin and other proteins. It is involved in the degradation of amyloid precursor protein to produce beta-amyloid peptides which are believed to be central to the pathophysiology of Alzheimer's disease. Previous reports have localized presenilin and nicastrin to the endoplasmic reticulum. However, during a proteomics-based characterization of lysosomal membrane proteins, a major spot observed on silver-stained IEF/SDS-PAGE gels was identified by mass spectrometric sequencing as nicastrin. Its M(r) corresponded to the reported mature M(r) for nicastrin, indicating that it is stable in the lysosomal environment. Furthermore, protease protection assays confirmed that nicastrin is contained in the outer lysosomal membrane, rather than in an internalized vesicle awaiting degradation, and that it is properly orientated with its amino-terminus facing the lysosomal lumen with its carboxyl-terminus facing the cytosol. We conclude that nicastrin is a resident lysosomal membrane protein.     

Mutational analysis of the hMSH6 gene in familial and early-onset colorectal and endometrial cancer in Israeli patients

Familial colorectal cancer (CRC) is noted in about 15% of incident CRC cases, and at times is hallmarked by an age at diagnosis less than 50 years. Familial adenomatous polyposis (FAP) and hereditary non-polyposis colon cancer (HNPCC) account for about 40% of familial cases. Thus, the majority of familial and early-onset CRC remain genetically elusive. Similarly, the majority of familial and early onset endometrial cancer (EC), the most prevalent extracolonic tumor in HNPCC, are genetically undefined. An attractive candidate is the hMSH6 gene. Israeli patients with early onset (age under 50 years) (n = 44) and familial nonsyndromic (n = 23) CRC, and women with familial clustering of EC or CRC (n = 12), and those diagnosed with EC at, or under, the age of 50 years (n = 5) were genotyped for germ-line mutations within the hMSH6 gene. Exon-specific PCR was followed by denaturing gradient gel electrophoresis (DGGE) analysis, complemented by DNA sequencing of abnormally migrating fragments. No patients displayed a truncating mutation, and 1 CRC patient harbored a novel missense mutation (V878A). In addition, 6 previously described polymorphisms were detected. In conclusion, mutations in the hMSH6 gene occur uncommonly in Israeli patients with familial and early-onset CRC and EC.