Tuesday, October 10, 2006

Autoimmunity and Ubiquitin ligases

drj writes "Mutations in the AIRE (autoimmune regulator) gene cause ‘autoimmune polyendocrinopathy–candidiasis–ectodermal dystrophy’ (APECED, OMIM 240300), a rare autoimmune disease marked by lymphocyte infiltration and antibody deposition in multiple organs (review). Known human AIRE mutant alleles are recessive and were identified by positional cloning at 21q22.3 in 1997. Mice deficient in AIRE also develop autoimmune disease. AIRE protein is mostly nuclear and can activate transcription when linked to a DNA binding domain. AIRE increases the ectopic (out of place) expression of a ‘substantial’ number of genes in the thymus, which may promote T cell tolerance (self shadow). Failure to encounter these proteins in the thymus may permit autoimmune T cells to survive and mature, leading to autoimmunity. Here, disease-causing mutations in AIRE are shown to abolish ubiquitin (Ub) ligase activity without reducing transcription activation, strongly suggesting that Ub ligation is AIRE’s primary activity. The Cbl family of Ub ligases are known to deactivate the T cell receptor by targeting the associated tyrosine kinases. Is it too simplistic to ask which is (are) AIRE’s mechanism(s)?
PubMed Uchida et al., J. Exp. Med. 199(2) 167-172, 2004"
AIRE Functions As an E3 Ubiquitin Ligase. Daisuke Uchida, Shigetsugu Hatakeyama, Akemi Matsushima, Hongwei Han, Satoshi Ishido, Hak Hotta, Jun Kudoh, Nobuyoshi Shimizu, Vassilis Doucas, Keiichi I. Nakayama, Noriyuki Kuroda, and Mitsuru Matsumoto J. Exp. Med. Volume 199, Number 2, January 19, 2004 167–172

Clinical trial ethics reconsidered?

drj writes "Ethical design of randomized controlled clinical trials has required that there be substantial uncertainty about which treatment is most likely to benefit the patient, a principle known as 'equipoise'. Fries and Krishnan examined all 45 trials reported at a professional rheumatology meeting and found that all trials gave results favorable to the industry sponsor, demonstrating a significant deviation from equipoise because the results were predictable. (Nearly all patients would be concerned with even a 70:30 outcome distribution.) The authors suggest that extensive preliminary findings produced a beneficial 'design bias'. This is good, they believe, because true equipoise is inefficient, exposes more patients to risk, and conflicts with other major ethical principles. They propose a principle of "positive expected outcomes". Is this a refreshing acknowledgement of reality and useful guide or just a rewording of accepted clinical practice where treatment group size already varies based on expected outcomes?"
Full text Fries & Krishnan, Arthr. Res. & Ther. 6(3), 2004. James F Fries and Eswar Krishnan "Equipoise, design bias, and randomized controlled trials: the elusive ethics of new drug development" Arthritis Research & Therapy Vol 6 No 3

Inflammatory mediator sustains SLE T cells

drj writes "Self-reactive antibodies are a hallmark of systemic lupus erythematosus (SLE, lupus), a life-threatening autoimmune disease that disproportionately affects women in their child bearing years. Production of these antibodies is driven by autoreactive T cells that are normally eliminated but persist in SLE patients. Xu and colleagues compared the activities of thousands of genes in the T cells of SLE patients and normal controls. They found that stimulatory conditions that caused normal T cells to be eliminated instead caused SLE T cells to increase their expression of cyclooxygenase-2 (COX-2) and survive. Moreover, inhibiting COX-2 activity reversed the abnormal resistance of SLE T cells. The increased COX-2 was specific to SLE T cells and did not occur in T cells from other autoimmune diseases or cancer cells. Certain COX-2 inhibitors but not others were able to restore normal responses to SLE T cells, providing a rational basis for the use of these drugs for therapy and suggesting approaches to designing more potent and specific therapeutic drugs for use in SLE.
PubMed Xu et al, Nat. Med. February 29, 2004. L, Zhang L, Yi Y, Kang HK, Datta SK. "Human lupus T cells resist inactivation and escape death by upregulating COX-2". Nature Medicine February 29, 2004"

Arthritis suppression by TNF alpha regulators

drj writes "Many rheumatoid arthritis patients are helped by treatments that block the inflammatory cytokine TNF alpha. TNF alpha production is reduced by two proteins that bind AU-rich regions of mRNA: TIA-1 inhibits protein translation and TTP promotes mRNA degradation. Mice deficient in either TIA-1 or TTP (gene “knockouts”) develop arthritis. Not surprisingly, Phillips and colleagues show that TIA-1/TTP double knockout mice develop worse arthritis. Single knockout macrophages contain more TNF alpha protein than normal macrophages and double knockout macrophages contain much more, most markedly the membrane bound form (mTNF alpha). Surprisingly, much less TNF alpha protein is secreted by double knockout macrophages than either single knockout, suggesting TIA-1 and TTP influence secretion or mTNF alpha processing. The investigation turned to the less usual suspects, neutrophils, which also make TNF alpha and are extraordinarily abundant in the bone marrow of double knockout mice. Indeed, activated bone marrow cells from double knockout mice express much more TNF alpha than single TTP knockout macrophages. However, purified neutrophils from TTP knockout mice show only a modest increase and double knockout show no further increase, leaving the origin of the increased TNF obscure. Although failing to establish a complete mechanism, this investigation demonstrates several important interactions and represents the kind of analysis that is necessary to dissect complex disease genetics.
PubMed Phillips et al. PNAS 101:2011-2016. February 17, 2004. Arthritis suppressor genes TIA-1 and TTP dampen the expression of tumor necrosis factor alpha, cyclooxygenase 2, and inflammatory arthritis Kristine Phillips, Nancy Kedersha, Lily Shen, Perry J. Blackshear, and Paul Anderson
Additional information: Macrophages and neutrophils were activated with bacterial endotoxin, LPS. Double knockout mice are born runts and remain about half the weight of single knockout or normal mice.