Rac1 Signaling Is Required for Insulin-Stimulated Glucose Uptake and Is Dysregulated in Insulin-Resistant Murine and Human Skeletal Muscle

The actin cytoskeleton–regulating GTPase Rac1 is required for insulin-stimulated GLUT4 translocation in cultured muscle cells. However, involvement of Rac1 and its downstream signaling in glucose transport in insulin-sensitive and insulin-resistant mature skeletal muscle has not previously been investigated. We hypothesized that Rac1 and its downstream target, p21-activated kinase (PAK), are regulators of insulin-stimulated glucose uptake in mouse and human skeletal muscle and are dysregulated in insulin-resistant states. Muscle-specific inducible Rac1 knockout (KO) mice and pharmacological inhibition of Rac1 were used to determine whether Rac1 regulates insulin-stimulated glucose transport in mature skeletal muscle. Furthermore, Rac1 and PAK1 expression and signaling were investigated in muscle of insulin-resistant mice and humans. Inhibition and KO of Rac1 decreased insulin-stimulated glucose transport in mouse soleus and extensor digitorum longus muscles ex vivo. Rac1 KO mice showed decreased insulin and glucose tolerance and trended toward higher plasma insulin concentrations after intraperitoneal glucose injection. Rac1 protein expression and insulin-stimulated PAK^Thr423 phosphorylation were decreased in muscles of high fat–fed mice. In humans, insulin-stimulated PAK activation was decreased in both acute insulin-resistant (intralipid infusion) and chronic insulin-resistant states (obesity and diabetes). These findings show that Rac1 is a regulator of insulin-stimulated glucose uptake and a novel candidate involved in skeletal muscle insulin resistance.Insulin increases glucose uptake in skeletal muscle by stimulating translocation of GLUT4 from intracellular compartments to the plasma membrane and transverse tubuli (1–4). Skeletal muscle accounts for up to 75% of postprandial glucose disposal in humans (5), and normal insulin action in skeletal muscle is therefore crucial for maintaining glucose homeostasis.The Rho family GTPase Rac1 has been shown to regulate insulin-stimulated GLUT4 translocation and glucose transport in cultured muscle cells (6–8). Insulin activates Rac1, which leads to reorganization of the cortical actin cytoskeleton. Downregulation of Rac1 by small interfering RNA prevents this process (7,9) and also abolishes insulin-stimulated glucose uptake and GLUT4 translocation in L6 myoblasts (6,7). In addition, expression of a constitutively active Rac1 increases GLUT4 translocation to the same level seen after maximal insulin stimulation in this cell line (6).Even though cultured muscle cell lines are powerful tools to understand intracellular mechanisms, they differ from mature skeletal muscle in the expression and reliance of various proteins in the regulation of insulin-stimulated glucose uptake (10). Cultured muscle myoblasts, although able to fuse into myotubes, do not reach the same end-stage differentiation (e.g., do not have cross striations and do not develop transverse tubules) as muscles in vivo and therefore do not fully mature into a system that mimics fully developed skeletal muscles (11,12). Furthermore, the location, expression, and insulin-stimulated GLUT4 translocation are very different in cultured cells compared with mature muscle and may not require the same trafficking steps (2,3,13,14). As a consequence, it is imperative to investigate the role of Rac1 in insulin-stimulated glucose uptake in fully matured skeletal muscle in order to understand its role in glucose metabolism. Furthermore, the importance of skeletal muscle Rac1 on whole-body glucose homeostasis has not been determined.Rac1 activates p21-activated kinase (PAK) by facilitating autophosphorylation of PAK on threonine 423 (p-PAK^Thr423), and this pathway induces actin remodeling of the actin cytoskeleton (15). Accordingly, disruption of the actin cytoskeleton by actin-depolymerizing agents, such as latrunculin B, inhibits insulin-stimulated GLUT4 translocation in L6 myotubes (16,17). Dynamic rearrangement of the actin cytoskeleton is thus necessary for insulin to induce GLUT4 translocation in these cells (18).These findings also apply to mature skeletal muscle, since latrunculin B inhibits insulin-stimulated glucose uptake in rat epitrochlearis muscle (19). Furthermore, Ueda et al. (20) recently showed that Rac1 is activated by insulin in mouse skeletal muscle and that insulin-stimulated GLUT4 translocation is decreased in muscle-specific Rac1 knockout (KO) mice. PAK1 was also recently shown to be implicated in the regulation of insulin-stimulated GLUT4 translocation in mouse skeletal muscle (21). However, GLUT4 translocation does not always mimic glucose uptake, and numerous studies have reported experimental conditions where GLUT4 translocation and transport can be clearly dissociated (22–27), suggesting that GLUT4 translocation is not always an adequate measure of the functional end point, glucose uptake. Thus, the involvement of Rac1 and its downstream signaling in insulin-stimulated glucose uptake in mature skeletal muscle has not yet been investigated, and Rac1-dependent signaling has not been characterized in animal or human models of insulin resistance.A decreased ability to rearrange the cortical actin cytoskeleton in response to insulin has been proposed as a central defect in insulin-resistant muscle cells (28–30). Although exposure to insulin resistance–inducing agents decreased Rac1 activation and GLUT4 translocation (7), only small reductions in Akt signaling were observed in L6 myotubes (8). It is therefore possible that Rac1 is a major regulator of glucose uptake in mature skeletal muscle, and its dysregulation might contribute to the phenotype of muscular insulin resistance and type 2 diabetes (T2D). In the current study, we hypothesized that activation of Rac1 and its downstream target, PAK, is crucial for insulin-induced glucose uptake in mature skeletal muscle and for maintaining whole-body glucose homeostasis. We further hypothesized that Rac1-dependent signaling is downregulated in insulin-resistant states.     

Patient reported outcome measures in women undergoing surgery for urinary incontinence and pelvic organ prolapse in Denmark, 2006–2011

Introduction and hypothesis

The aim of this study was to evaluate the impact of urogynecological surgery on quality of life based on patient reported outcome measures (PROMs).

Methods

Data were retrieved from the Danish Urogynaecological Database. Inclusion criteria were Danish women undergoing surgery for urinary incontinence (UI) or pelvic organ prolapse (POP) from 2006 to 2011. Using frequency of symptoms and a visual analogue scale (VAS) both pre- and postoperatively, their severity of symptoms and quality of life were measured by questionnaires.

Results

During the study period, 20,629 urogynecological procedures were performed. The questionnaires on severity of symptoms and the VAS had been completed both pre- and postoperatively for approximately one third of women undergoing surgery. For UI surgery, 83 % had improved symptoms, 13 % were unchanged, and 4 % had worse symptoms postoperatively. For POP surgery, 80, 17, and 3 % were improved, unchanged, and worsened, respectively. The postoperative bother of symptoms and interference in everyday life evaluated by VAS were significantly reduced for both UI [preoperative median VAS score 9, postoperative median score 1 (p?<?0.001)] and POP [8 preoperatively and 0 postoperatively (p?<?0.001)].

Conclusions

Based on PROMs, surgery for UI and POP is effective in alleviating symptoms associated with UI or POP, and it can improve quality of life in symptomatic women. Pre- and postoperative questionnaires are useful tools in assessing symptomatic outcome measures after surgery.     

Epilepsy in Individuals with a History of Asperger’s Syndrome: A Danish Nationwide Register-Based Cohort Study

We performed a nationwide, register-based retrospective follow-up study of epilepsy in all people who were born between January 1, 1980 and June 29, 2006 and registered in the Danish Psychiatric Central Register with Asperger’s syndrome on February 7, 2011. All 4,180 identified cases with AS (3,431 males and 749 females) were screened through the nationwide Danish National Hospital Register (DNHR) with respect to epilepsy. Mean age at follow-up was 18.1 years (range 4–31 years). Of the 4,180 individuals with AS, 164 (3.9 %) were registered with at least one epilepsy diagnosis in the DNHR, which is significantly increased (p < 0.0001) relative to the same age group in the general population, where an estimate is about 2.0 %.     

Implications of caries diagnostic strategies for clinical management decisions

Baelum V, Hintze H, Wenzel A, Danielsen B, Nyvad B. Implications of caries diagnostic strategies for clinical management decisions. Community Dent Oral Epidemiol 2011. © 2011 John Wiley & Sons A/S Abstract – Objectives: In clinical practice, a visual–tactile caries examination is frequently supplemented by bitewing radiography. This study evaluated strategies for combining visual–tactile and radiographic caries detection methods and determined their implications for clinical management decisions in a low‐caries population. Methods: Each of four examiners independently examined preselected contacting interproximal surfaces in 53 dental students aged 20–37 years using a visual–tactile examination and bitewing radiography. The visual–tactile examination distinguished between noncavitated and cavitated lesions while the radiographic examination determined lesion depth. Direct inspection of the surfaces following tooth separation for the presence of cavitated or noncavitated lesions was the validation method. The true‐positive rate (i.e. the sensitivity) and the false‐positive rate (i.e. 1‐specificity) were calculated for each diagnostic strategy. Results: Visual–tactile examination provided a true‐positive rate of 34.2% and a false‐positive rate of 1.5% for the detection of a cavity. The combination of a visual–tactile and a radiographic examination using the lesion in dentin threshold for assuming cavitation had a true‐positive rate of 76.3% and a false‐positive rate of 8.2%. When diagnostic observations were translated into clinical management decisions using the rule that a noncavitated lesion should be treated nonoperatively and a cavitated lesion operatively, our results showed that the visual–tactile method alone was the superior strategy, resulting in most correct clinical management decisions and most correct decisions regarding the choice of treatment.     

Experimental and Numerical Investigation of an Axial Rotary Blood Pump

Left ventricular assist devices (LVADs) have become a standard therapy for patients with severe heart failure. As low blood trauma in LVADs is important for a good clinical outcome, the assessment of the fluid loads inside the pump is critical. More specifically, the flow features on the surfaces where the interaction between blood and artificial material happens is of great importance. Therefore, experimental data for the near‐wall flows in an axial rotary blood pump were collected and directly compared to computational fluid dynamic results. For this, the flow fields based on unsteady Reynolds‐averaged Navier–Stokes simulations‐computational fluid dynamics (URANS‐CFD) of an axial rotary blood pump were calculated and compared with experimental flow data at one typical state of operation in an enlarged model of the pump. The focus was set on the assessment of wall shear stresses (WSS) at the housing wall and rotor gap region by means of the wall‐particle image velocimetry technique, and the visualization of near‐wall flow structures on the inner pump surfaces by a paint erosion method. Additionally, maximum WSS and tip leakage volume flows were measured for 13 different states of operation. Good agreement between CFD and experimental data was found, which includes the location, magnitude, and direction of the maximum and minimum WSS and the presence of recirculation zones on the pump stators. The maximum WSS increased linearly with pressure head. They occurred at the upstream third of the impeller blades and exceeded the critical values with respect to hemolysis. Regions of very high shear stresses and recirculation zones could be identified and were in good agreement with simulations. URANS‐CFD, which is often used for pump performance and blood damage prediction, seems to be, therefore, a valid tool for the assessment of flow fields in axial rotary blood pumps. The magnitude of maximum WSS could be confirmed and were in the order of several hundred Pascal.     

Mortality and Causes of Death in Patients With Osteogenesis Imperfecta: A Register‐Based Nationwide Cohort Study

Osteogenesis imperfecta (OI) is a hereditary connective tissue disease that causes frequent fractures. Little is known about causes of death and length of survival in OI. The objective of this work was to calculate the risk and cause of death, and the median survival time in patients with OI. This study was a Danish nationwide, population‐based and register‐based cohort study. We used National Patient Register data from 1977 until 2013 with complete long‐term follow‐up. Participants comprised all patients registered with the diagnosis of OI from 1977 until 2013, and a reference population matched five to one to the OI cohort. We calculated hazard ratios for all‐cause mortality and subhazard ratios for cause‐specific mortality in a comparison of the OI cohort and the reference population. We also calculated all‐cause mortality hazard ratios for males, females, and age groups (0 to 17.99 years, 18.00 to 34.99 years, 35.00 to 54.99 years, 55.00 to 74.99 years, and >75 years). We identified 687 cases of OI (379 women) and included 3435 reference persons (1895 women). A total of 112 patients with OI and 257 persons in the reference population died during the observation period. The all‐cause mortality hazard ratio between the OI cohort and the reference population was 2.90. The median survival time for males with OI was 72.4 years, compared to 81.9 in the reference population. The median survival time for females with OI was 77.4 years, compared to 84.5 years in the reference population. Patients with OI had a higher risk of death from respiratory diseases, gastrointestinal diseases, and trauma. We were limited by the lack of clinical information about phenotype and genotype of the included patients. Patients with OI had a higher mortality rate throughout their life compared to the general population. © 2016 American Society for Bone and Mineral Research.