Genetics of rheumatoid arthritis: what have we learned?

Rheumatoid arthritis (RA) is a chronic autoimmune disease affecting 0.5–1% of the population worldwide. The disease has a heterogeneous character, including clinical subsets of anti-citrullinated protein antibody (ACPA)-positive and APCA-negative disease. Although the pathogenesis of RA is poorly understood, progress has been made in identifying genetic factors that contribute to the disease. The most important genetic risk factor for RA is found in the human leukocyte antigen (HLA) locus. In particular, the HLA molecules carrying the amino acid sequence QKRAA, QRRAA, or RRRAA at positions 70–74 of the DRβ1 chain are associated with the disease. The HLA molecules carrying these “shared epitope” sequences only predispose for ACPA-positive disease. More than two decades after the discovery of HLA-DRB1 as a genetic risk factor, the second genetic risk factor for RA was identified in 2003. The introduction of new techniques, such as methods to perform genome-wide association has led to the identification of more than 20 additional genetic risk factors within the last 4 years, with most of these factors being located near genes implicated in immunological pathways. These findings underscore the role of the immune system in RA pathogenesis and may provide valuable insight into the specific pathways that cause RA.     

The rise in testicular androgens during the first days of treatment with an LHRH agonist in the dog can be blocked by aminoglutethimide or ketoconazole

Up to day 6 of treatment of adult dogs, daily subcutaneous administration of 50 micrograms of the LHRH agonist [D-Trp6, des-Gly-NH2-10]LHRH ethylamide causes up to a 3-fold increase in serum testosterone (T) concentration which is followed by a progressive decrease to castration levels (less than or equal to 0.2 ng/ml) at later time intervals (up to 21 days, the last time interval studied). Both aminoglutethimide and ketoconazole, two inhibitors of steroid biosynthesis, cause a 30-40% rise in serum T when administered alone. However, either drug administered in combination with the LHRH agonist completely blocks the transient rise in serum T observed when the LHRH agonist is administered alone. On the other hand, the LHRH agonist prevents the secondary rise in steroid secretion observed when either of the two inhibitors of steroid secretion is used alone. Administration of the pure antiandrogen Flutamide alone or in combination with LHRH-A and an inhibitor of steroid biosynthesis does not influence serum T levels. When the serum levels of pregnenolone, 17-OH-pregnenolone, progesterone, 17-OH-progesterone, dehydroepiandrosterone (DHEA), androstenedione (delta 4-dione), androst-5-ene-3 beta, 17 beta-diol (delta 5-diol), T, dihydrotestosterone (DHT), androstane-3 alpha, 17 beta-diol, androstane-3 beta. 17 beta-diol and 17 beta-estradiol (E2) are analyzed in detail, it can be seen that both aminoglutethimide and ketoconazole not only prevent the rise in serum steroids observed during the first 8 days of treatment with the LHRH agonist but that both compounds enhance the inhibitory effect of the LHRH agonist at later time intervals. A predominant inhibitory effect of ketoconazole is exerted on 17,20-desmolase activity. Aminoglutethimide has little influence on the loss of serum LH bioactivity induced by the LHRH agonist while ketoconazole stimulates the concentration of serum bioactive LH in the absence or presence of simultaneous treatment with the LHRH agonist. The present data clearly demonstrate that aminoglutethimide or ketoconazole can prevent the rise in serum androgens accompanying the first days of treatment with an LHRH agonist in the dog. Moreover, after 3 weeks of treatment, the inhibitory effect of the LHRH agonist on serum androgen levels is enhanced by addition of aminoglutethimide or ketoconazole. Moreover, Flutamide does not interfere with the inhibitory action of the LHRH agonist, aminoglutethimide or ketoconazole, thus suggesting that maximal inhibition of androgen action is likely to be achieved by a combination of these drugs.     

Phagosomes fuse with late endosomes and/or lysosomes by extension of membrane protrusions along microtubules: role of Rab7 and RILP

Nascent phagosomes must undergo a series of fusion and fission reactions to acquire the microbicidal properties required for the innate immune response. Here we demonstrate that this maturation process involves the GTPase Rab7. Rab7 recruitment to phagosomes was found to precede and to be essential for their fusion with late endosomes and/or lysosomes. Active Rab7 on the phagosomal membrane associates with the effector protein RILP (Rab7-interacting lysosomal protein), which in turn bridges phagosomes with dynein-dynactin, a microtubule-associated motor complex. The motors not only displace phagosomes in the centripetal direction but, strikingly, promote the extension of phagosomal tubules toward late endocytic compartments. Fusion of tubules with these organelles was documented by fluorescence and electron microscopy. Tubule extension and fusion with late endosomes and/or lysosomes were prevented by expression of a truncated form of RILP lacking the dynein-dynactin-recruiting domain. We conclude that full maturation of phagosomes requires the retrograde emission of tubular extensions, which are generated by activation of Rab7, recruitment of RILP, and consequent association of phagosomes with microtubule-associated motors.     

Transforming growth factor beta inhibits proliferation of somatic cells without influencing germ cell number in the chicken embryonic ovary

The gonadal development of chicken embryo is regulated by hormones and growth factors. Transforming growth factor beta (TGF-β) isoforms may play a critical role in the regulation of growth in chicken gonads. We have investigated the effect of the TGF-β isoforms on the number of germ and somatic cells in the ovary of the chicken embryo. Ovaries were obtained from chicken embryos at 9 days of incubation. They were organ-cultured for 72 h in groups treated with TGF-β1, TGF-β2, soluble betaglycan, TGF-β1 plus soluble betaglycan, or TGF-β2 plus soluble betaglycan, and untreated (control). TGF-β1 and TGF-β2 diminished the somatic cell number in the ovary of the chicken embryo at this age by inhibiting the proliferation of the somatic cells without increasing apoptosis. On the other hand, TGF-β1 and TGF-β2 did not affect the number of germ cells in the cultured ovary. The capacity of TGF-β1 and TGF-β2 to diminish the number of somatic cells in the ovary was blocked with soluble betaglycan, a natural TGF-β antagonist. However, changes in the location of germ cells within the ovary suggested that TGF-β promoted the migration of the germ cells from the ovarian cortex to the medulla. Thus, TGF-β affects germ and somatic cells in the ovary of the 9-day-old chicken embryo and inhibits the proliferation of somatic cells.This work was supported by DGAPA-UNAM (IN214403) and CONACYT (45030).     

Potential role of annexin AnnAt1 from Arabidopsis thaliana in pH-mediated cellular response to environmental stimuli

Plant annexins, Ca(2+)- and membrane-binding proteins, are probably implicated in the cellular response to stress resulting from acidification of cytosol. To understand how annexins can contribute to cellular ion homeostasis, we investigated the pH-induced changes in the structure and function of recombinant annexin AnnAt1 from Arabidopsis thaliana. The decrease of pH from 7.0 to 5.8 reduced the time of the formation of ion channels by AnnAt1 in artificial lipid membranes from 3.5 h to 15-20 min and increased their unitary conductance from 32 to 63 pS. These changes were accompanied by an increase in AnnAt1 hydrophobicity as revealed by hydrophobicity predictions, by an increase in fluorescence of 2-(p-toluidino)naphthalene-6-sulfonic acid (TNS) bound to AnnAt1 and fluorescence resonance energy transfer from AnnAt1 tryptophan residues to TNS. Concomitant lipid partition of AnnAt1 at acidic pH resulted in its partial protection from proteolytic digestion. Secondary structures of AnnAt1 determined by circular dichroism and infrared spectroscopy were also affected by lowering the pH from 7.2 to 5.2. These changes were characterized by an increase in beta-sheet content at the expense of alpha-helical structures, and were accompanied by reversible formation of AnnAt1 oligomers as probed by ultracentrifugation in a sucrose gradient. A further decrease of pH from 5.2 to 4.5 or lower led to the formation of irreversible aggregates and loss of AnnAt1 ionic conductance. Our findings suggest that AnnAt1 can sense changes of the pH milieu over the pH range from 7 to 5 and respond by changes in ion channel conductance, hydrophobicity, secondary structure of the protein and formation of oligomers. Further acidification irreversibly inactivated AnnAt1. We suggest that the pH-sensitive ion channel activity of AnnAt1 may play a role in intracellular ion homeostasis.     

Y-chromosomal diversity in Lebanon is structured by recent historical events

Lebanon is an eastern Mediterranean country inhabited by approximately four million people with a wide variety of ethnicities and religions, including Muslim, Christian, and Druze. In the present study, 926 Lebanese men were typed with Y-chromosomal SNP and STR markers, and unusually, male genetic variation within Lebanon was found to be more strongly structured by religious affiliation than by geography. We therefore tested the hypothesis that migrations within historical times could have contributed to this situation. Y-haplogroup J*(xJ2) was more frequent in the putative Muslim source region (the Arabian Peninsula) than in Lebanon, and it was also more frequent in Lebanese Muslims than in Lebanese non-Muslims. Conversely, haplogroup R1b was more frequent in the putative Christian source region (western Europe) than in Lebanon and was also more frequent in Lebanese Christians than in Lebanese non-Christians. The most common R1b STR-haplotype in Lebanese Christians was otherwise highly specific for western Europe and was unlikely to have reached its current frequency in Lebanese Christians without admixture. We therefore suggest that the Islamic expansion from the Arabian Peninsula beginning in the seventh century CE introduced lineages typical of this area into those who subsequently became Lebanese Muslims, whereas the Crusader activity in the 11(th)-13(th) centuries CE introduced western European lineages into Lebanese Christians.