Hyperglycemia potentiates H(2)O(2) production in adipocytes and enhances insulin signal transduction: potential role for oxidative inhibition of thiol-sensitive protein-tyrosine phosphatases

Insulin signal transduction in adipocytes is accompanied by a burst of cellular hydrogen peroxide (H(2)O(2)) that facilitates insulin signaling by inhibiting thiol-dependent protein-tyrosine phosphatases (PTPs) that are negative regulators of insulin action. As hyperglycemia is associated with increased cellular reactive oxygen species, we postulated that high glucose conditions might potentiate the H(2)O(2) generated by insulin and modulate insulin-stimulated protein phosphorylation. Basal H(2)O(2) generation was increased threefold in differentiated 3T3-L1 adipocytes by growth in 25 mM glucose versus 5 mM glucose. High glucose increased the sensitivity of the insulin-stimulated H(2)O(2) signal to lower concentrations of insulin. Basal endogenous total PTP activity and the activity of PTP1B, a PTP implicated in the negative regulation of insulin signaling, were reduced in high glucose conditions, and their further reduction by insulin stimulation was more enhanced in high versus low glucose medium. Phosphorylation of the insulin receptor, IRS-1, and Akt in response to insulin was also significantly enhanced in high glucose conditions, especially at submaximal insulin concentrations. In primary rat adipocytes, high glucose increased insulin-stimulated H(2)O(2) production and potentiated the oxidative inhibition of total PTP and PTP1B activity; however, insulin signaling was not enhanced in the primary cells in high glucose apparently due to cross-regulation of insulin-stimulated protein phosphorylation by activation of protein kinase C (PKC). These studies indicate that high glucose can enhance insulin stimulated H(2)O(2) generation and augment oxidative PTP inhibition in cultured and primary adipocytes, but the overall balance of insulin signal transduction is determined by additional signal effects in high glucose, including the activation of PKC.     

Structural basis for p50RhoGAP BCH domain–mediated regulation of Rho inactivation

Spatiotemporal regulation of signaling cascades is crucial for various biological pathways, under the control of a range of scaffolding proteins. The BNIP-2 and Cdc42GAP Homology (BCH) domain is a highly conserved module that targets small GTPases and their regulators. Proteins bearing BCH domains are key for driving cell elongation, retraction, membrane protrusion, and other aspects of active morphogenesis during cell migration, myoblast differentiation, and neuritogenesis. We previously showed that the BCH domain of p50RhoGAP (ARHGAP1) sequesters RhoA from inactivation by its adjacent GAP domain; however, the underlying molecular mechanism for RhoA inactivation by p50RhoGAP remains unknown. Here, we report the crystal structure of the BCH domain of p50RhoGAP Schizosaccharomyces pombe and model the human p50RhoGAP BCH domain to understand its regulatory function using in vitro and cell line studies. We show that the BCH domain adopts an intertwined dimeric structure with asymmetric monomers and harbors a unique RhoA-binding loop and a lipid-binding pocket that anchors prenylated RhoA. Interestingly, the β5-strand of the BCH domain is involved in an intermolecular β-sheet, which is crucial for inhibition of the adjacent GAP domain. A destabilizing mutation in the β5-strand triggers the release of the GAP domain from autoinhibition. This renders p50RhoGAP active, thereby leading to RhoA inactivation and increased self-association of p50RhoGAP molecules via their BCH domains. Our results offer key insight into the concerted spatiotemporal regulation of Rho activity by BCH domain–containing proteins.

Small GTPases are molecular switches that cycle between an active GTP-bound state and an inactive GDP-bound state and are primarily involved in cytoskeletal reorganization during cell motility, morphogenesis, and cytokinesis (1, 2). These small GTPases are tightly controlled by activators and inactivators, such as guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs), respectively (3, 4), which are multidomain proteins that are themselves regulated through their interactions with other proteins, lipids, secondary messengers, and/or by posttranslational modifications (5–7). Despite our understanding of the mechanisms of action of GTPases, GAPs, and GEFs, little is known about how they are further regulated by other cellular proteins in tightly controlled local environments.The BNIP-2 and Cdc42GAP Homology (BCH) domain has emerged as a highly conserved and versatile scaffold protein domain that targets small GTPases, their GEFs, and GAPs to carry out various cellular processes in a spatial, temporal, and kinetic manner (8–15). BCH domain–containing proteins are classified into a distinct functional subclass of the CRAL_TRIO/Sec14 superfamily, with ∼175 BCH domain–containing proteins (in which 14 of them are in human) present across a range of eukaryotic species (16). Some well-studied BCH domain–containing proteins include BNIP-2, BNIP-H (CAYTAXIN), BNIP-XL, BNIP-Sα, p50RhoGAP (ARHGAP1), and BPGAP1 (ARHGAP8), with evidence to show their involvement in cell elongation, retraction, membrane protrusion, and other aspects of active morphogenesis during cell migration, growth activation and suppression, myoblast differentiation, and neuritogenesis (17–21). Aside from interacting with small GTPases and their regulators, some of these proteins can also associate with other signaling proteins, such as fibroblast growth factor receptor tyrosine kinases, myogenic Cdo receptor, p38-MAP kinase, Mek2/MP1, and metabolic enzymes, such as glutaminase and ATP-citrate lyase (17–26). Despite the functional diversity and versatility of BCH domain–containing proteins, the structure of the BCH domain and its various modes of interaction remain unknown. The BCH domain resembles the Sec14 domain (from the CRAL-TRIO family) (16, 27, 28), a domain with lipid-binding characteristics, which may suggest that the BCH domain could have a similar binding strategy. However, to date, the binding and the role of lipids in BCH domain function remain inconclusive.Of the BCH domain–containing proteins, we have focused on the structure and function of p50RhoGAP. p50RhoGAP comprises an N-terminal BCH domain and a C-terminal GAP domain separated by a proline-rich region. We found that p50RhoGAP contains a noncanonical RhoA-binding motif in its BCH domain and is associated with GAP-mediated cell rounding (13). Further, we showed previously that deletion of the BCH domain dramatically enhanced the activity of the adjacent GAP domain (13); however, the full dynamics of this interaction is unclear. Previously, it has been reported that the BCH and other domains regulate GAP activity in an autoinhibited manner (18, 21, 29, 30) involving the interactions of both the BCH and GAP domains, albeit the mechanism remains to be investigated. It has also been shown that a lipid moiety on Rac1 (a Rho GTPase) is necessary for its inactivation by p50RhoGAP (29, 31), which may imply a role in lipid binding. An understanding of how the BCH domain coordinates with the GAP domain to affect the local activity of RhoA and other GTPases would offer a previously unknown insight into the multifaceted regulation of Rho GTPase inactivation.To understand the BCH domain–mediated regulation of p50RhoGAP and RhoA activities, we have determined the crystal structure of a homologous p50RhoGAP BCH domain from S. pombe for functional interrogation. We show that the BCH domain adopts an intertwined dimeric structure with asymmetric monomers and harbors a unique RhoA-interacting loop and a lipid-binding pocket. Our results show that the lipid-binding region of the BCH domain helps to anchor the prenylation tail of RhoA while the loop interacts directly with RhoA. Moreover, we show that a mutation in the β5-strand releases the autoinhibition of the GAP domain by the BCH domain. This renders the GAP domain active, leading to RhoA inactivation and the associated phenotypic effects in yeast and HeLa cells. The released BCH domain also contributes to enhanced p50RhoGAP–p50RhoGAP interaction. Our findings offer crucial insights into the regulation of Rho signaling by BCH domain–containing proteins.     

Correlation between NT proBNP and left ventricular ejection fraction in elderly patients presenting to emergency department with dyspnoea

ObjectiveShortness of breath is a common complaint for which the elderly seek medical attention in the emergency department (ED). Differentiating cardiac from respiratory causes of dyspnoea in this population is quite a challenge. N Terminal pro brain-natriuretic-peptide (NT proBNP) has been studied extensively as a biomarker of left ventricular (LV) failure.MethodsThe NT proBNP was measured in 100 patients above 60 years of age who presented to the ED with shortness of breath. The level was compared with echocardiographic findings to assess correlation with ejection fraction (EF).ResultsThe NT proBNP values increased significantly as the functional severity of heart failure (HF) increased (P < 0.001). The mean NT proBNP level was 1503.33 pg/mL. Patients with respiratory causes of dyspnoea had a mean NT proBNP level of 309.28 pg/mL with normal LV function.ConclusionThe NT proBNP levels had a good correlation with worsening LVEF.     

SCAI expert consensus update on best practices in the cardiac catheterization laboratory

The current document commissioned by the Society for Cardiovascular Angiography and Interventions (SCAI) and endorsed by the American College of Cardiology, the American Heart Association, and Heart Rhythm Society represents a comprehensive update to the 2012 and 2016 consensus documents on patient-centered best practices in the cardiac catheterization laboratory. Comprising updates to staffing and credentialing, as well as evidence-based updates to the pre-, intra-, and post-procedural logistics, clinical standards and patient flow, the document also includes an expanded section on CCL governance, administration, and approach to quality metrics. This update also acknowledges the collaboration with various specialties, including discussion of the heart team approach to management, and working with electrophysiology colleagues in particular. It is hoped that this document will be utilized by hospitals, health systems, as well as regulatory bodies involved in assuring and maintaining quality, safety, efficiency, and cost-effectiveness of patient throughput in this high volume area.     

Evaluation of Bone Density Around the Implants Placed Using Drilling Technique and Bone Expansion Technique: An In vivo Study

Bone density is a key parameter in determining the surgical procedure of implant placement and for the predictability of successful implant treatment. Several clinical studies have shown lower survival rates of implants in maxilla which was attributed to poor bone quality. The present study compared the variations in the pre-operative and post-operative bone density values in Hounsfield units using CT between drilling technique and bone expansion technique at 0.25 and 1.0 mm sections at two sites which were selected in maxillary arch between the second premolar regions of either quadrants and results have shown bone expansion technique is superior to drilling technique in division III bone.     

Intratumoral administration of paclitaxel in an in situ gelling poloxamer 407 formulation

In order to examine the efficacy of paclitaxel (Taxol, Bristol-Myers Squibb) after administration locally at the tumor site, we have developed a thermo-reversible gelling formulation in poloxamer 407 (Pluronic F-127) solution. Paclitaxel was incorporated in poloxamer 407 [20% (w/w)] at 0.5- and 1.0-mg/mL concentrations. The in vitro release studies were carried out in phosphate-buffered saline (pH 7.4) at 37 degrees C. Control and paclitaxel-poloxamer 407 formulations were administered intratumorally at a dose of 20 mg/kg in B16F1 melanoma-bearing mice. The change in tumor volume as a function of time and the survival of treated animals were used as measures of efficacy. Poloxamer 407 solution undergoes a reversible sol-gel transition when the temperature is raised to above 21 degrees C. In vitro paclitaxel release from poloxamer 407 gels was very slow (only 6.1% after 6 hr) probably due to the poor aqueous solubility of the drug. Significant enhancement in the anti-tumor efficacy was noted following intratumoral administration of paclitaxel-poloxamer 407 formulation. The initial tumor growth rate was delayed by 67% and the tumor volume doubling time was increased by 72% relative to saline control. In addition, more than 91% of the tumor-bearing animals that received paclitaxel in poloxamer 407 gel survived on day 15 post-administration as compared to 58% in the control group. The results of this study show significant benefit of paclitaxel for solid tumor when administered locally in an in situ gelling poloxamer 407 formulation.