Coordinated Regulation of Vasopressin Inactivation and Glucose Uptake by Action of TUG Protein in Muscle

In adipose and muscle cells, insulin stimulates the exocytic translocation of vesicles containing GLUT4, a glucose transporter, and insulin-regulated aminopeptidase (IRAP), a transmembrane aminopeptidase. A substrate of IRAP is vasopressin, which controls water homeostasis. The physiological importance of IRAP translocation to inactivate vasopressin remains uncertain. We previously showed that in skeletal muscle, insulin stimulates proteolytic processing of the GLUT4 retention protein, TUG, to promote GLUT4 translocation and glucose uptake. Here we show that TUG proteolysis also controls IRAP targeting and regulates vasopressin action in vivo. Transgenic mice with constitutive TUG proteolysis in muscle consumed much more water than wild-type control mice. The transgenic mice lost more body weight during water restriction, and the abundance of renal AQP2 water channels was reduced, implying that vasopressin activity is decreased. To compensate for accelerated vasopressin degradation, vasopressin secretion was increased, as assessed by the cosecreted protein copeptin. IRAP abundance was increased in T-tubule fractions of fasting transgenic mice, when compared with controls. Recombinant IRAP bound to TUG, and this interaction was mapped to a short peptide in IRAP that was previously shown to be critical for GLUT4 intracellular retention. In cultured 3T3-L1 adipocytes, IRAP was present in TUG-bound membranes and was released by insulin stimulation. Together with previous results, these data support a model in which TUG controls vesicle translocation by interacting with IRAP as well as GLUT4. Furthermore, the effect of IRAP to reduce vasopressin activity is a physiologically important consequence of vesicle translocation, which is coordinated with the stimulation of glucose uptake.

Endoproteolytic cleavage of TUG protein regulates GLUT4 glucose transporter translocation

To promote glucose uptake into fat and muscle cells, insulin causes the translocation of GLUT4 glucose transporters from intracellular vesicles to the cell surface. Previous data support a model in which TUG traps GLUT4-containing vesicles and tethers them intracellularly in unstimulated cells and in which insulin mobilizes this pool of vesicles by releasing this tether. Here we show that TUG undergoes site-specific endoproteolytic cleavage, which separates a GLUT4-binding, N-terminal region of TUG from a C-terminal region previously suggested to bind an intracellular anchor. Cleavage is accelerated by insulin stimulation in 3T3-L1 adipocytes and is highly dependent upon adipocyte differentiation. The N-terminal TUG cleavage product has properties of a novel 18-kDa ubiquitin-like modifier, which we call TUGUL. The C-terminal product is observed at the expected size of 42 kDa and also as a 54-kDa form that is released from membranes into the cytosol. In transfected cells, intact TUG links GLUT4 to PIST and also binds Golgin-160 through its C-terminal region. PIST is an effector of TC10α, a GTPase previously shown to transmit an insulin signal required for GLUT4 translocation, and we show using RNAi that TC10α is required for TUG proteolytic processing. Finally, we demonstrate that a cleavage-resistant form of TUG does not support highly insulin-responsive GLUT4 translocation or glucose uptake in 3T3-L1 adipocytes. Together with previous results, these data support a model whereby insulin stimulates TUG cleavage to liberate GLUT4 storage vesicles from the Golgi matrix, which promotes GLUT4 translocation to the cell surface and enhances glucose uptake.

Dual-mode of insulin action controls GLUT4 vesicle exocytosis

Insulin releases an intracellular brake and promotes fusion pore expansion to translocate GLUT4 vesicles, and switches vesicle trafficking between distinct exocytic circuits.

Insulin stimulates translocation of GLUT4 storage vesicles (GSVs) to the surface of adipocytes, but precisely where insulin acts is controversial. Here we quantify the size, dynamics, and frequency of single vesicle exocytosis in 3T3-L1 adipocytes. We use a new GSV reporter, VAMP2-pHluorin, and bypass insulin signaling by disrupting the GLUT4-retention protein TUG. Remarkably, in unstimulated TUG-depleted cells, the exocytic rate is similar to that in insulin-stimulated control cells. In TUG-depleted cells, insulin triggers a transient, twofold burst of exocytosis. Surprisingly, insulin promotes fusion pore expansion, blocked by acute perturbation of phospholipase D, which reflects both properties intrinsic to the mobilized vesicles and a novel regulatory site at the fusion pore itself. Prolonged stimulation causes cargo to switch from ∼60 nm GSVs to larger exocytic vesicles characteristic of endosomes. Our results support a model whereby insulin promotes exocytic flux primarily by releasing an intracellular brake, but also by accelerating plasma membrane fusion and switching vesicle traffic between two distinct circuits.

Intracellular retention and insulin-stimulated mobilization of GLUT4 glucose transporters

GLUT4 glucose transporters are expressed nearly exclusively in adipose and muscle cells, where they cycle to and from the plasma membrane. In cells not stimulated with insulin, GLUT4 is targeted to specialized GLUT4 storage vesicles (GSVs), which sequester it away from the cell surface. Insulin acts within minutes to mobilize these vesicles, translocating GLUT4 to the plasma membrane to enhance glucose uptake. The mechanisms controlling GSV sequestration and mobilization are poorly understood. An insulin-regulated aminopeptidase that cotraffics with GLUT4, IRAP, is required for basal GSV retention and insulin-stimulated mobilization. TUG and Ubc9 bind GLUT4, and likely retain GSVs within unstimulated cells. These proteins may be components of a retention receptor, which sequesters GLUT4 and IRAP away from recycling vesicles. Insulin may then act on this protein complex to liberate GLUT4 and IRAP, discharging GSVs into a recycling pathway for fusion at the cell surface. How GSVs are anchored intracellularly, and how insulin mobilizes these vesicles, are the important topics for ongoing research. Regulation of GLUT4 trafficking is tissue-specific, perhaps in part because the formation of GSVs requires cell type-specific expression of sortilin. Proteins controlling GSV retention and mobilization can then be more widely expressed. Indeed, GLUT4 likely participates in a general mechanism by which the cell surface delivery of various membrane proteins can be controlled by extracellular stimuli. Finally, it is not known if defects in the formation or intracellular retention of GSVs contribute to human insulin resistance, or play a role in the pathogenesis of type 2 diabetes.

Efficacy and safety of etoricoxib 30 mg and celecoxib 200 mg in the treatment of osteoarthritis in two identically designed, randomized, placebo-controlled, non-inferiority studies

OBJECTIVE

To compare the efficacy of etoricoxib 30 mg with the generally maximum recommended dose of celecoxib, 200 mg, in the treatment of osteoarthritis (OA) in two identically designed studies.

METHODS

Two multi-centre, 26-week, double-blind, placebo-controlled, non-inferiority studies were conducted, enrolling patients who were prior non-steroidal anti-inflammatory drug (NSAID) or acetaminophen users. There were 599 patients in study 1 and 608 patients in study 2 randomized 4:4:1:1 to etoricoxib 30 mg qd, celecoxib 200 mg qd or one of two placebo groups for 12 weeks. After 12 weeks, placebo patients were evenly distributed to etoricoxib or celecoxib based on their initial enrollment randomization schedule. The primary hypothesis was that etoricoxib 30 mg would be at least as effective as celecoxib 200 mg for the time-weighted average change from baseline over 12 weeks for Western Ontario and McMaster (WOMAC) Pain Subscale, WOMAC Physical Function Subscale and Patient Global Assessment of Disease Status. Active treatments were also assessed over the full 26 weeks. Adverse experiences were collected for safety assessment.

RESULTS

In both studies, etoricoxib was non-inferior to celecoxib for all three efficacy outcomes over 12 and 26 weeks; both were superior to placebo (P < 0.001) for all three outcomes in each study over 12 weeks. The safety and tolerability of etoricoxib 30 mg qd and celecoxib 200 mg qd were similar over 12 and 26 weeks.

CONCLUSIONS

Etoricoxib 30 mg qd was at least as effective as celecoxib 200 mg qd and had similar safety in the treatment of knee and hip OA; both were superior to placebo. ClinicalTrials.gov Identifiers: NCT00092768; NCT00092791.

Oral polymeric N-acetyl-D-glucosamine and osteoarthritis

Many patients with arthritis are using alternative modes of therapy, including nutritional supplements, to treat their arthritis. Most patients never tell their doctors that they are taking alternative medications, and few doctors even ask about such activities. Over-the-counter supplements are expensive and consume large amounts of patients' healthcare dollars. Glucosamine has been widely touted as being an effective arthritis treatment. The authors designed and undertook a study to test the efficacy of a polymer of N-acetyl-D-glucosamine (NAG), or POLY-Nag, in a double-blind, placebo-controlled study in patients with osteoarthritis. Results indicate that POLY-Nag may be useful in treating patients with osteoarthritis.

Osteoarthritis

Arthritis is a common, disabling condition that affects an increasing percentage of the population. This article includes discussion of new theories of risk factors and treatment paradigms.

Specific cyclooxygenase-2 (COX-2) inhibitors

Nonsteroidal anti-inflammatory drugs (NSAIDs) are currently among the most widely prescribed drugs worldwide. Their therapeutic benefits and their side effects in the gastrointestinal tract and kidney, as well as in hemostasis, are of great importance in modern medicine. Within the past decade, new insights into how NSAIDs produce both their therapeutic benefits and their serious side effects have been discovered. It is now known that there are two froms of the cyclooxygenase (COX) enzyme that metabolize arachidonic acid into prostaglandins. Drugs that specifically inhibit the COX-2 enzyme were formulated and put into clinical trials during the past 5 years. These drugs are now available to treat patients in the United States. Specific COX-2 inhibitors offer the benefit of being able to treat the pain and inflammation of arthritis with potentially little risk of serious gastrointestinal injury.

Gastropathy induced by nonsteroidal anti-inflammatory drugs: prescribing patterns among geriatric practitioners

The objective of this study was to determine patterns among geriatric practitioners in prescribing agents that protect the gastrointestinal tract when nonsteroidal anti-inflammatory drug (NSAID) treatment is started for elderly patients. A questionnaire describing five scenarios of elderly patients requiring NSAID therapy asked respondents to choose gastrointestinal-protective agents for each scenario. Respondents were then asked to what extent four established risk factors for NSAID gastropathy (age, previous peptic ulcer, previous gastrointestinal bleeding, and heart disease) affected their choices. The choice of gastrointestinal-protective agent was compared with the training and experience of the respondents. This self-administered survey was provided to 821 randomly selected physicians from the membership of the American Geriatrics Society throughout the United States and Puerto Rico. Statistical Package for the Social Sciences (SPSS), version 6.1.4, was used to obtain frequencies. Of 821 surveys, 229 (28%) were returned. It was found that well elderly patients and nursing home residents were not treated with any gastrointestinal-protective agent by 64% (well elderly patients) and 32% (nursing home residents) of respondents. Among respondents who would prescribe, about half would choose misoprostol for a well elderly patient or a nursing home resident, whereas half or more preferred histamine H2-receptor antagonists. Twenty-three percent would not prescribe misoprostol when NSAID therapy was resumed after an active ulcer had healed, and 68% preferred H2 antagonists in that setting. The difference in response attributable to training/experience was less than 9%. Factors that did not affect prescribing patterns included the patient's age (15% to 62%) and heart disease (44% to 50%). The study concluded that age and heart disease are risk factors to which physicians give less consideration when choosing gastrointestinal-protective agents. Although misoprostol is the only agent approved by the Food and Drug Administration for prophylaxis against NSAID gastropathy, 23% of respondents chose not to prescribe misoprostol when NSAID therapy was resumed after an active ulcer had healed. Histamine H2-receptor antagonists were preferred over misoprostol for well elderly patients and nursing home residents. Training and experience were not responsible for differences among respondents' prescribing patterns.

Juvenile rheumatoid arthritis

Musculoskeletal problems account for the majority of initial complaints attended to by primary care physicians. It is likely that a child who eventually has juvenile rheumatoid arthritis diagnosed will initially be evaluated by a family physician or a pediatrician. Primary care physicians will play an increasingly important role in management of juvenile rheumatoid arthritis, as the availability of specialists in many communities is limited, and access to them may be further limited by managed care initiatives. This article offers a brief review of the definition and classification of juvenile rheumatoid arthritis and introduces a diagnostic algorithm to provide a simplified approach toward evaluating children with arthritis. Treatment and outcomes are summarized in text and graphic formats.

Biochemical characterization of ADP-ribose polymer metabolism in SLE

The metabolism of poly(ADP-ribose) in peripheral blood mononuclear (PBM) cells was studied in 13 patients with systemic lupus erythematosus (SLE) and in 12 age and sex matched controls. Poly(ADP-ribose) polymerase activity was measured as the net accumulation of ADP-ribose polymers during the conversion of 32P-NAD to poly(ADP-ribose) in PBM cells in vitro. The control population showed a mean activity of 418 +/- 91(s.d.)pmol ADP-ribose/10 min/10(6) cells. The SLE population was more heterogeneous and showed a lower mean of 225 +/- 147(s.d.)pmol ADP-ribose/10 min/10(6) cells. The mechanism of decreased ADP-ribose polymer accumulation was investigated. Measurements of turnover of the ADP-ribose polymers and its substrate, NAD+, showed that diminished ADP-ribose polymer accumulation in SLE subjects resulted from decreased poly(ADP-ribose) synthesis and not from altered rates of polymer turnover or NAD utilization. Western blot analyses of enzyme protein levels, kinetic studies of poly(ADP-ribose) polymerase activity and analyses of polymer size distribution suggested that the mechanisms of poly(ADP-ribose) synthesis in SLE cells is not altered but that the number of active poly(ADP-ribose) polymerase molecules is reduced.

Understanding antinuclear antibodies

The American College of Rheumatology (formerly the American Rheumatism Association) diagnostic criteria for connective tissue disorders frequently include positive antinuclear antibody (ANA) assays. Proper interpretation of these tests requires an understanding of the principles governing ANA assays. Assay results are reported in two ways: as titers and as descriptions of fluorescent patterns. A titer is a quantitative measure of ANAs in serum. Different patterns of immunofluorescence are associated with different subsets of collagen vascular disease. Positive results can occur in the absence of connective tissue disease. Accurate diagnosis of connective tissue disorders requires judicious use of ANA assays as well as skillful interpretation of the results.

Pain management in the older adult with rheumatoid arthritis or osteoarthritis

The study's major purpose was to explore the pain management of the older adult with rheumatic disease. Medication, rest, heat, distraction, exercise, and talking with others were methods most often used by older adults (n = 31). Methods identified by them as most helpful included medication, rest, and heat. When the pain management techniques of those adults 65 and over were compared with those of younger adults (n = 51), several differences were noted. The combined number of methods used by the younger group was significantly greater, and they rated relaxation techniques as being significantly more helpful. Increasing the elderly arthritis patient's repertoire of pain management modalities and measuring the ongoing individual effectiveness of the individual and combined methods used are identified as needs to be addressed in improving pain management.

Increased carbonyl content of proteins in synovial fluid from patients with rheumatoid arthritis

The carbonyl content of proteins in the synovial fluid (SF) of patients with rheumatoid arthritis was significantly (p less than or equal to 0.10) elevated over levels in the SF of patients with osteoarthritis (OA). Other indicators of oxidative damage including catalse, ceruloplasmin, ferritin and superoxide dismutase also showed statistically significant differences (p less than or equal to 0.05) compared to patients with OA.

Acute visual loss in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) often presents as a multisystem disease that can be difficult to diagnose. Although ocular symptoms are infrequent, actual acute visual loss has been reported. A review of four cases of acute visual loss from a lupus clinic revealed that two patients had visual loss as a presenting sign of SLE. One had bilateral occipital lobe infarctions, the other multiple cotton wool spots and an attenuated retinal vascular system. Of the two patients with documented SLE prior to the onset of visual problems, one presented with a coincidental retinal tear and the other with retinal phlebitis.

The redox state in lymphocytes from patients with rheumatoid arthritis

Our study was designed to quantitate levels of NAD+, NADH, NADP(H), and ATP in peripheral blood lymphocytes with and without mitogenic stimulation from patients with rheumatoid arthritis (RA). No differences were found in patients with RA and healthy controls. Our data suggest the ability of the redox system of circulating peripheral lymphocytes to respond to mitogenic stimulation in patients with RA is not markedly impaired.