Endothelial Poldip2 regulates sepsis-induced lung injury via Rho pathway activation

AIMS

Sepsis-induced lung injury is associated with significant morbidity and mortality. Previously, we showed that heterozygous deletion of polymerase δ-interacting protein 2 (Poldip2) was protective against sepsis-induced lung injury. Since endothelial barrier disruption is thought to be the main mechanism of sepsis-induced lung injury, we sought to determine if the observed protection was specifically due to the effect of reduced endothelial Poldip2.

METHODS AND RESULTS

Endothelial-specific Poldip2 knock-out mice (EC-/-) and their wild-type littermates (EC+/+) were injected with saline or lipopolysaccharide (18 mg/kg) to model sepsis-induced lung injury. At 18 h post-injection mice, were euthanized and bronchoalveolar lavage (BAL) fluid and lung tissue were collected to assess leucocyte infiltration. Poldip2 EC-/- mice showed reduced lung leucocyte infiltration in BAL (0.21 ± 0.9×106 vs. 1.29 ± 1.8×106 cells/mL) and lung tissue (12.7 ± 1.8 vs. 23 ± 3.7% neutrophils of total number of cells) compared to Poldip2 EC+/+ mice. qPCR analysis of the lung tissue revealed a significantly dampened induction of inflammatory gene expression (TNFα 2.23 ± 0.39 vs. 4.15 ± 0.5-fold, IκBα 4.32 ± 1.53 vs. 8.97 ± 1.59-fold), neutrophil chemoattractant gene expression (CXCL1 68.8 ± 29.6 vs. 147 ± 25.7-fold, CXCL2 65 ± 25.6 vs. 215 ± 27.3-fold) and a marker of endothelial activation (VCAM1 1.25 ± 0.25 vs. 3.8 ± 0.38-fold) in Poldip2 EC-/- compared to Poldip2 EC+/+ lungs. An in vitro model using human pulmonary microvascular endothelial cells was used to assess the effect of Poldip2 knock-down on endothelial activation and permeability. TNFα-induced endothelial permeability and VE-cadherin disruption were significantly reduced with siRNA-mediated knock-down of Poldip2 (5 ± 0.5 vs. 17.5 ± 3-fold for permeability, 1.5 ± 0.4 vs. 10.9 ± 1.3-fold for proportion of disrupted VE-cadherin). Poldip2 knock-down altered expression of Rho-GTPase-related genes, which correlated with reduced RhoA activation by TNFα (0.94 ± 0.05 vs. 1.29 ± 0.01 of relative RhoA activity) accompanied by redistribution of active-RhoA staining to the centre of the cell.

CONCLUSION

Poldip2 is a potent regulator of endothelial dysfunction during sepsis-induced lung injury, and its endothelium-specific inhibition may provide clinical benefit.

Mitochondrial Fission Mediates Endothelial Inflammation

Endothelial inflammation and mitochondrial dysfunction have been implicated in cardiovascular diseases, yet, a unifying mechanism tying them together remains limited. Mitochondrial dysfunction is frequently associated with mitochondrial fission/fragmentation mediated by the GTPase Drp1 (dynamin-related protein 1). Nuclear factor (NF)-κB, a master regulator of inflammation, is implicated in endothelial dysfunction and resultant complications. Here, we explore a causal relationship between mitochondrial fission and NF-κB activation in endothelial inflammatory responses. In cultured endothelial cells, TNF-α (tumor necrosis factor-α) or lipopolysaccharide induces mitochondrial fragmentation. Inhibition of Drp1 activity or expression suppresses mitochondrial fission, NF-κB activation, vascular cell adhesion molecule-1 induction, and leukocyte adhesion induced by these proinflammatory factors. Moreover, attenuations of inflammatory leukocyte adhesion were observed in Drp1 heterodeficient mice as well as endothelial Drp1 silenced mice. Intriguingly, inhibition of the canonical NF-κB signaling suppresses endothelial mitochondrial fission. Mechanistically, NF-κB p65/RelA seems to mediate inflammatory mitochondrial fission in endothelial cells. In addition, the classical anti-inflammatory drug, salicylate, seems to maintain mitochondrial fission/fusion balance against TNF-α via inhibition of NF-κB. In conclusion, our results suggest a previously unknown mechanism whereby the canonical NF-κB cascade and a mitochondrial fission pathway interdependently regulate endothelial inflammation.

Involvement of Senescence and Mitochondrial Fission in Endothelial Cell Pro-Inflammatory Phenotype Induced by Angiotensin II

Angiotensin II (AngII) has a crucial role in cardiovascular pathologies, including endothelial inflammation and premature vascular aging. However, the precise molecular mechanism underlying aging-related endothelial inflammation induced by AngII remains elusive. Here, we have tested a hypothesis in cultured rat aortic endothelial cells (ECs) that the removal of AngII-induced senescent cells, preservation of proteostasis, or inhibition of mitochondrial fission attenuates the pro-inflammatory EC phenotype. AngII stimulation in ECs resulted in cellular senescence assessed by senescence-associated β galactosidase activity. The number of β galactosidase-positive ECs induced by AngII was attenuated by treatment with a senolytic drug ABT737 or the chemical chaperone 4-phenylbutyrate. Monocyte adhesion assay revealed that the pro-inflammatory phenotype in ECs induced by AngII was alleviated by these treatments. AngII stimulation also increased mitochondrial fission in ECs, which was mitigated by mitochondrial division inhibitor-1. Pretreatment with mitochondrial division inhibitor-1 attenuated AngII-induced senescence and monocyte adhesion in ECs. These findings suggest that mitochondrial fission and endoplasmic reticulum stress have causative roles in endothelial senescence-associated inflammatory phenotype induced by AngII exposure, thus providing potential therapeutic targets in age-related cardiovascular diseases.

Loss of dynamic regulation of G protein-coupled receptor kinase 2 by nitric oxide leads to cardiovascular dysfunction with aging

Nitric oxide (NO) and S-nitrosothiol (SNO) are considered cardio- and vasoprotective substances. We now understand that one mechanism in which NO/SNOs provide cardiovascular protection is through their direct inhibition of cardiac G protein-coupled receptor (GPCR) kinase 2 (GRK2) activity via S-nitrosylation of GRK2 at cysteine 340 (C340). This maintains GPCR homeostasis, including β-adrenergic receptors, through curbing receptor GRK2-mediated desensitization. Previously, we have developed a knockin mouse (GRK2-C340S) where endogenous GRK2 is resistant to dynamic S-nitrosylation, which led to increased GRK2 desensitizing activity. This unchecked regulation of cardiac GRK2 activity resulted in significantly more myocardial damage after ischemic injury that was resistant to NO-mediated cardioprotection. Although young adult GRK2-C340S mice show no overt phenotype, we now report that as these mice age, they develop significant cardiovascular dysfunction due to the loss of SNO-mediated GRK2 regulation. This pathological phenotype is apparent as early as 12 mo of age and includes reduced cardiac function, increased cardiac perivascular fibrosis, and maladaptive cardiac hypertrophy, which are common maladies found in patients with cardiovascular disease (CVD). There are also vascular reactivity and aortic abnormalities present in these mice. Therefore, our data demonstrate that a chronic and global increase in GRK2 activity is sufficient to cause cardiovascular remodeling and dysfunction, likely due to GRK2’s desensitizing effects in several tissues. Because GRK2 levels have been reported to be elevated in elderly CVD patients, GRK2-C340 mice can give insight into the aged-molecular landscape leading to CVD.

NEW & NOTEWORTHY Research on G protein-coupled receptor kinase 2 (GRK2) in the setting of cardiovascular aging is largely unknown despite its strong established functions in cardiovascular physiology and pathophysiology. This study uses a mouse model of chronic GRK2 overactivity to further investigate the consequences of long-term GRK2 on cardiac function and structure. We report for the first time that chronic GRK2 overactivity was able to cause cardiac dysfunction and remodeling independent of surgical intervention, highlighting the importance of GRK activity in aged-related heart disease.

An acceleration in hypertension-related mortality for middle-aged and older Americans, 1999-2016: An observational study

BACKGROUND

Hypertension-related mortality has been increasing in recent years; however, limited information exists concerning rate, temporal, secular, and geographic trends in the United States.

METHODS AND RESULTS

Using CDC death certificate data spanning 1999-2016, we sought to delineate trends in deaths attributable to an underlying cause of hypertension using joinpoint regression and proportion testing. From 1999-2016, the hypertension-related mortality rate increased by 36.4% with an average annual percent change (AAPC) of 1.8% for individuals ≥ 35 years of age. Interestingly, there was a notable acceleration in the AAPC of hypertension mortality between 2011 and 2016 (2.7% per year). This increase was due to a significant uptick in mortality for individuals ≥ 55 years of age with the greatest AAPC occurring in individuals 55-64 (4.5%) and 65-74 (5.1%) years of age. Increased mortality and AAPC were pervasive throughout sex, ethnicity, and White and American Indian or Alaska Native race, but not Black or African American race. From 2011-2016, there were significant increases in AAPC for hypertension-related mortality with contributing causes of atrial fibrillation, heart failure, diabetes, obesity, and vascular dementia. Elevated mortality was observed for conditions with a contributing cause of hypertension that included chronic obstructive pulmonary disease, diabetes, Alzheimer's, Parkinson's, and all types of falls. Geographically, increases in AAPCs and mortality rates were observed for 25/51 States between 2011 and 2016.

CONCLUSIONS

Our results indicate hypertension-related mortality may have accelerated since 2011 for middle-aged and older Americans, which may create new challenges in care and healthcare planning.

Poldip2 mediates blood-brain barrier disruption in a model of sepsis-associated encephalopathy

Background

Sepsis-associated encephalopathy (SAE), a diffuse cerebral dysfunction in the absence of direct CNS infection, is associated with increased rates of mortality and morbidity in patients with sepsis. Increased cytokine production and disruption of the blood-brain barrier (BBB) are implicated in the pathogenesis of SAE. The induction of pro-inflammatory mediators is driven, in part, by activation of NF-κΒ. Lipopolysaccharide (LPS), an endotoxin produced by gram-negative bacteria, potently activates NF-κΒ and its downstream targets, including cyclooxygenase-2 (Cox-2). Cox-2 catalyzes prostaglandin synthesis and in the brain prostaglandin, E2 is capable of inducing endothelial permeability. Depletion of polymerase δ-interacting protein 2 (Poldip2) has previously been reported to attenuate BBB disruption, possibly via regulation of NF-κΒ, in response to ischemic stroke. Here we investigated Poldip2 as a novel regulator of NF-κΒ/cyclooxygenase-2 signaling in an LPS model of SAE.

Methods

Intraperitoneal injections of LPS (18 mg/kg) were used to induce BBB disruption in Poldip2^+/+ and Poldip2^+/− mice. Changes in cerebral vascular permeability and the effect of meloxicam, a selective Cox-2 inhibitor, were assessed by Evans blue dye extravasation. Cerebral cortices of Poldip2^+/+ and Poldip2^+/− mice were further evaluated by immunoblotting and ELISA. To investigate the role of endothelial Poldip2, immunofluorescence microscopy and immunoblotting were performed to study the effect of siPoldip2 on LPS-mediated NF-κΒ subunit p65 translocation and Cox-2 induction in rat brain microvascular endothelial cells. Finally, FITC-dextran transwell assay was used to assess the effect of siPoldip2 on LPS-induced endothelial permeability.

Results

Heterozygous deletion of Poldip2 conferred protection against LPS-induced BBB permeability. Alterations in Poldip2^+/+ BBB integrity were preceded by induction of Poldip2, p65, and Cox-2, which was not observed in Poldip2^+/− mice. Consistent with these findings, prostaglandin E2 levels were significantly elevated in Poldip2^+/+ cerebral cortices compared to Poldip2^+/− cortices. Treatment with meloxicam attenuated LPS-induced BBB permeability in Poldip2^+/+ mice, while having no significant effect in Poldip2^+/− mice. Moreover, silencing of Poldip2 in vitro blocked LPS-induced p65 nuclear translocation, Cox-2 expression, and endothelial permeability.

Conclusions

These data suggest Poldip2 mediates LPS-induced BBB disruption by regulating NF-κΒ subunit p65 activation and Cox-2 and prostaglandin E2 induction. Consequently, targeted inhibition of Poldip2 may provide clinical benefit in the prevention of sepsis-induced BBB disruption.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1575-4) contains supplementary material, which is available to authorized users.

Reactive Oxygen Species in Metabolic and Inflammatory Signaling

Reactive oxygen species (ROS) are well known for their role in mediating both physiological and pathophysiological signal transduction. Enzymes and subcellular compartments that typically produce ROS are associated with metabolic regulation, and diseases associated with metabolic dysfunction may be influenced by changes in redox balance. In this review, we summarize the current literature surrounding ROS and their role in metabolic and inflammatory regulation, focusing on ROS signal transduction and its relationship to disease progression. In particular, we examine ROS production in compartments such as the cytoplasm, mitochondria, peroxisome, and endoplasmic reticulum and discuss how ROS influence metabolic processes such as proteasome function, autophagy, and general inflammatory signaling. We also summarize and highlight the role of ROS in the regulation metabolic/inflammatory diseases including atherosclerosis, diabetes mellitus, and stroke. In order to develop therapies that target oxidative signaling, it is vital to understand the balance ROS signaling plays in both physiology and pathophysiology, and how manipulation of this balance and the identity of the ROS may influence cellular and tissue homeostasis. An increased understanding of specific sources of ROS production and an appreciation for how ROS influence cellular metabolism may help guide us in the effort to treat cardiovascular diseases.

Polymerase-δ-interacting protein 2 activates the RhoGEF epithelial cell transforming sequence 2 in vascular smooth muscle cells

Polymerase-δ-interacting protein 2 (Poldip2) controls a wide variety of cellular functions and vascular pathologies. To mediate these effects, Poldip2 interacts with numerous proteins and generates reactive oxygen species via the enzyme NADPH oxidase 4 (Nox4). We have previously shown that Poldip2 can activate the Rho family GTPase RhoA, another signaling node within the cell. In this study, we aimed to better understand how Poldip2 activates Rho family GTPases and the functions of the involved proteins in vascular smooth muscle cells (VSMCs). RhoA is activated by guanine nucleotide exchange factors. Using nucleotide-free RhoA (isolated from bacteria) to pulldown active RhoGEFs, we found that the RhoGEF epithelial cell transforming sequence 2 (Ect2) is activated by Poldip2. Ect2 is a critical RhoGEF for Poldip2-mediated RhoA activation, because siRNA against Ect2 prevented Poldip2-mediated RhoA activity (measured by rhotekin pulldowns). Surprisingly, we were unable to detect a direct interaction between Poldip2 and Ect2, as they did not coimmunoprecipitate. Nox4 is not required for Poldip2-driven Ect2 activation, as Poldip2 overexpression induced Ect2 activation in Nox4 knockout VSMCs similar to wild-type cells. However, antioxidant treatment blocked Poldip2-induced Ect2 activation. This indicates a novel reactive oxygen species-driven mechanism by which Poldip2 regulates Rho family GTPases. Finally, we examined the function of these proteins in VSMCs, using siRNA against Poldip2 or Ect2 and determined that Poldip2 and Ect2 are both essential for vascular smooth muscle cell cytokinesis and proliferation.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Abstract P243: Vascular Drp1 Mediates Angiotensin II-Induced Cardiovascular Hypertrophy via Global as Well as Selective de novo Protein Synthesis

Mitochondrial fission has been implicated in various cardiovascular and metabolic diseases but the role of the mitochondrial fission inducer Drp1 in regulating hypertension and cardiovascular remodeling remains unclear. To study the involvement of Drp1 in cardiovascular hypertrophy, rat aortic vascular smooth muscle cells (VSMCs) are infected with dominant negative (dn) Drp1 adenovirus and stimulated with 100 nM angiotensin II (AngII). In vivo, tamoxiphen-inducible SMMHC-Cre+/- Drp1 floxed mice and control mice are infused with AngII (1000ng/kg/min) for 2 weeks. In VSMCs, AngII-induced mitochondrial fission was attenuated with AT1 blocker RNH6270 (ARB) as well as with dnDrp1 (100 moi). ARB and dnDrp1 treatment also inhibited AngII-enhanced global as well as specific de novo protein synthesis evaluated by SunSet assay. To identify potential mediators downstream of Drp1-mitochondrial fission contributing to VSMC hypertrophy, shotgun proteomic analysis was performed on proteins extracted from AngII or vehicle treated VSMC with dnDrp1 or control adenovirus infection. 22 exclusively regulated proteins induced by AngII and attenuated by dnDrp1 were identified including previously known AngII targets, HMGB1 and PAIRB. In addition, ARB and dnDrp1 inhibited AngII-induced enhancement of mitochondrial ox-phosphorylation and oxidative stress (assessed with mito-timer adenovirus). In vivo, VSMC specific DRP1 silencing suppressed AngII-induced cardiac hypertrophy assessed with heart weight/body weight ratio Mean±SEM: 6.33±0.14 vs 5.25±0.07 (p<0.001) as well as with echocardiogram: LVPWd 1.46±0.02 vs 0.81±0.03 (p<0.001). However, both control and the Drp1 silenced mice developed hypertension when infused with AngII as assessed by DSI radio-telemetry system. In conclusion, these data suggest that Drp1 mediates AngII-induced global as well as specific de novo protein synthesis thereby contributing to cardiovascular hypertrophic remodeling.

Vascular ADAM17 (a Disintegrin and Metalloproteinase Domain 17) Is Required for Angiotensin II/β-Aminopropionitrile-Induced Abdominal Aortic Aneurysm

Angiotensin II (AngII)-activated epidermal growth factor receptor has been implicated in abdominal aortic aneurysm (AAA) development. In vascular smooth muscle cells (VSMCs), AngII activates epidermal growth factor receptor via a metalloproteinase, ADAM17 (a disintegrin and metalloproteinase domain 17). We hypothesized that AngII-dependent AAA development would be prevented in mice lacking ADAM17 in VSMCs. To test this concept, control and VSMC ADAM17-deficient mice were cotreated with AngII and a lysyl oxidase inhibitor, β-aminopropionitrile, to induce AAA. We found that 52.4% of control mice did not survive because of aortic rupture. All other surviving control mice developed AAA and demonstrated enhanced expression of ADAM17 in the AAA lesions. In contrast, all AngII and β-aminopropionitrile-treated VSMC ADAM17-deficient mice survived and showed reduction in external/internal diameters (51%/28%, respectively). VSMC ADAM17 deficiency was associated with lack of epidermal growth factor receptor activation, interleukin-6 induction, endoplasmic reticulum/oxidative stress, and matrix deposition in the abdominal aorta of treated mice. However, both VSMC ADAM17-deficient and control mice treated with AngII and β-aminopropionitrile developed comparable levels of hypertension. Treatment of C57Bl/6 mice with an ADAM17 inhibitory antibody but not with control IgG also prevented AAA development. In conclusion, VSMC ADAM17 silencing or systemic ADAM17 inhibition seems to protect mice from AAA formation. The mechanism seems to involve suppression of epidermal growth factor receptor activation.

Caveolin-1 Deletion Prevents Hypertensive Vascular Remodeling Induced by Angiotensin II

It has been proposed that membrane microdomains, caveolae, in vascular cells are critical for signal transduction and downstream functions induced by angiotensin II (AngII). We have tested our hypothesis that caveolin-1 (Cav1), a major structural protein of vascular caveolae, plays a critical role in the development of vascular remodeling by AngII via regulation of epidermal growth factor receptor and vascular endothelial adhesion molecule-1. Cav1^-/- and control Cav^+/+ mice were infused with AngII for 2 weeks to induce vascular remodeling and hypertension. On AngII infusion, histological assessments demonstrated medial hypertrophy and perivascular fibrosis of aorta and coronary and renal arteries in Cav1^+/+ mice compared with sham-operated Cav1^+/+ mice. AngII-infused Cav1^+/+ mice also showed a phenotype of cardiac hypertrophy with increased heart weight to body weight ratio compared with control Cav1^+/+ mice. In contrast, Cav1^-/- mice infused with AngII showed attenuation of vascular remodeling but not cardiac hypertrophy. Similar levels of AngII-induced hypertension were found in both Cav1^+/+ and Cav1^-/- mice as assessed by telemetry. In Cav1^+/+ mice, AngII enhanced tyrosine-phosphorylated epidermal growth factor receptor staining in the aorta, which was attenuated in Cav1^-/- mice infused with AngII. Enhanced Cav1 and vascular endothelial adhesion molecule-1 expression was also observed in aorta from AngII-infused Cav1^+/+ mice but not in Cav1^-/- aorta. Experiments with vascular cells further provided a potential mechanism for our in vivo findings. These data suggest that Cav1, and presumably caveolae, in vascular smooth muscle and the endothelium plays a critical role in vascular remodeling and inflammation independent of blood pressure or cardiac hypertrophy regulation.

Abstract 012: Involvement of Drp1, A Mitochondrial Fission Inducer, in Angiotensin Ii-induced Hypertensive Vascular Remodeling in vitro and in vivo

Mitochondrial dysfunction has been implicated in various types of cardiovascular diseases which may involve overload and de-compensation in mitochondrial quality/quantity control. However, limited mechanistic insight is available regarding the contribution and mechanism of mitochondrial quality control in hypertension. In the present study, we tested our hypothesis that enhancement of mitochondrial fission via Drp1 activation in vascular smooth muscle cells (VSMCs) is involved in hypertensive vascular remodeling. Rat aortic VSMCs pretreated with adenovirus encoding Drp1 siRNA (Ad-siDrp1) or control non-silencing RNA (100 moi) were stimulated with 100 nM angiotensin II (AngII) up to 72 h. 8 week old male C57/BL6 mice were infused with (1000 ng/kg/min) for 2 weeks with or without treatment of Drp1 inhibitor mdivi1 (25 mg/kg ip every other day). In VSMCs, AngII induced transient mitochondrial fission (max at 2-4 h assessed by mito-tracker staining) associated with Drp1 phosphorylation at Ser616 (10-30 min). Pretreatment of ad-siDrp1 (100 moi) or mdivi1 (5 μM) attenuated AngII-induced mitochondrial fission. Ad-siDrp1 or mdivi1 also attenuated AngII-induced enhancements of mitochondrial reactive oxygen species (ROS) generation, total cell protein, cell volume and extracellular collagen content. In mice, mdivi1 significantly suppressed vascular hypertrophy and perivascular fibrosis induced by AngII in aorta, heart and kidney. mdivi1 also inhibited AngII-induced left ventricular hypertrophy assessed by heart weight body weight ratio (mg/g: 7.8±0.9 vs 6.3±0.2 p<0.01) as well as by echocardiogram. However, mdivi1 did not affect hypertension induced by AngII assessed by telemetry (mean arterial pressure: sham 150±8 vs mdivi1 155±7 mmHg). KDEL and nitro-tyrosine staining of the heart and kidney suggest attenuation of vascular ER stress and oxidative stress, respectively. In conclusion, this data suggests that Drp1-dependent mitochondrial fission contributes to AngII-induced cardiovascular remodeling independently of hypertension via enhancement of mitochondrial ROS and ER stress in target organs.

Abstract 087: Mitochondrial Fission Inducer, Dynamin-Related Protein 1 (DRP1), is Required for Endothelial Inflammatory Responses

Among various cardiovascular diseases, hypertension (HTN) is considered to be a disease plagued by chronic low-grade inflammation associated with endothelial dysfunction. Interestingly, recent studies have identified mitochondrial adaptation and/or dysfunction as components to hypertensive vascular dysfunction. While mitochondria are indispensable to maintain cellular metabolism, they also participate in adaptive and maladaptive cell/tissue responses via several retro grade signaling pathways. DRP1 plays a major role in mitochondrial quality control. However, whether DRP1 is involved in mitochondrial dysfunction and endothelial inflammation during development of HTN remains unknown. In the present study, we tested the hypothesis that inflammatory stimuli, through DRP1-dependent mitochondrial alteration, enhance endothelial inflammation. In cultured rat aortic endothelial cells (RAECs), TNFα (10 μg/mL) transiently induced mitochondrial fission maximally at 3h which was inhibited using a mitochondrial fission inhibitor, Mdivi1 (10 μM) (0.16±0.04 vs 0.10±0.02 mitochondria fragmentation count with MitoTracker, p<.01 ). TNFα and FCCP (a fission agonist, 10 μM) increased THP-1 monocyte adhesion to RAECs, which was also inhibited with Mdivi1 (256±17 vs 139±16 for TNFα, 238±30 vs 156±14 for FCCP, attached cells per field scanned, p<.01 ). Likewise, mdivi1 and adenoviruses encoding siRNA for DRP1 or dominant-negative K38A DRP1 (50 moi) attenuated TNFα-induced VCAM-1 induction in RAECs. TNFα increased aerobic respiration, which was prevented by mdivi1 or ER stress inhibitor PBA (10 mM). Inhibition of ER stress, glycolysis or mitochondrial respiration using PBA, 2-DG (1 mg/mL) or oligomycin (1 μM) prevented VCAM-1 induction. However, suppression of TNFα-induced mitochondrial ROS production by mito-Tempo (25 nM) was unable to prevent VCAM-1 induction. In C57BL6 mice receiving AngII (1000 ng/kg/min, 2 weeks) infusion, treatment with Mdivi-1 (25 mg/kg ip every other day) or PBA (1g/kg/day) prevented vascular VCAM-1 induction. In conclusion, our data suggests a critical role for ER stress and subsequent functional and structural remodeling of mitochondria induced by DRP1 in mediating endothelial inflammatory activation in HTN.

Vascular ADAM17 as a Novel Therapeutic Target in Mediating Cardiovascular Hypertrophy and Perivascular Fibrosis Induced by Angiotensin II

Angiotensin II (AngII) has been strongly implicated in hypertension and its complications. Evidence suggests the mechanisms by which AngII elevates blood pressure and enhances cardiovascular remodeling and damage may be distinct. However, the signal transduction cascade by which AngII specifically initiates cardiovascular remodeling, such as hypertrophy and fibrosis, remains insufficiently understood. In vascular smooth muscle cells, a metalloproteinase ADAM17 mediates epidermal growth factor receptor transactivation, which may be responsible for cardiovascular remodeling but not hypertension induced by AngII. Thus, the objective of this study was to test the hypothesis that activation of vascular ADAM17 is indispensable for vascular remodeling but not for hypertension induced by AngII. Vascular ADAM17-deficient mice and control mice were infused with AngII for 2 weeks. Control mice infused with AngII showed cardiac hypertrophy, vascular medial hypertrophy, and perivascular fibrosis. These phenotypes were prevented in vascular ADAM17-deficient mice independent of blood pressure alteration. AngII infusion enhanced ADAM17 expression, epidermal growth factor receptor activation, and endoplasmic reticulum stress in the vasculature, which were diminished in ADAM17-deficient mice. Treatment with a human cross-reactive ADAM17 inhibitory antibody also prevented cardiovascular remodeling and endoplasmic reticulum stress but not hypertension in C57Bl/6 mice infused with AngII. In vitro data further supported these findings. In conclusion, vascular ADAM17 mediates AngII-induced cardiovascular remodeling via epidermal growth factor receptor activation independent of blood pressure regulation. ADAM17 seems to be a unique therapeutic target for the prevention of hypertensive complications.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

Abstract 557: Pharmacological Inhibition of ADAM17 by a Human-Cross Reactive Antibody and Selective Inhibitor JG26 Prevents Vascular Fibrosis Induced by Angiotensin II in vivo and in vitro

In cultured vascular smooth muscle cells (VSMCs), we have shown that a metalloprotease, ADAM17, mediates EGF receptor (EGFR) transactivation induced by angiotensin II (AngII). We have also shown that in mice with AngII infusion, EGFR inhibitor erlotinib prevents vessel remodeling independently from hypertension. In the present study, we hypothesized that pharmacological inhibition of ADAM17 prevents AngII-induced vascular fibrosis in vivo and in vitro. A novel human-cross reactive ADAM17 inhibitory antibody, A9(B8), (10 mg/kg ip on day 1 and 7) was utilized in C57Bl/6 mice with AngII infusion (1000 ng/kg/min for 2 weeks). A novel ADAM17 inhibitor JG26 (1 μM) was utilized in cultured rat aortic VSMCs stimulated with 100 nM AngII. A9(B8) but not control IgG treatment attenuated perivascular fibrosis and vascular hypertrophy in mouse coronary arteries (assessed by Sirius Red staining) infused with AngII. A9(B8) also attenuated cardiac hypertrophy (assessed by echocardiogram and heart body weight ratio) but not hypertension in mice with AngII infusion. In VSMCs, 30 min pretreatment of JG26 inhibited AngII-induced extracellular collagen accumulation at 48 h (assessed by a Sirius Red quantification kit). JG26 also inhibited AngII-induced EGFR transactivation (2 and 10 min) and ERK activation (10 min) in VSMCs. We conclude that inhibition of ADAM17 is an effective approach to attenuate pathophysiological cardiovascular remodeling in an AngII-dependent model of hypertension. These data highlight ADAM17 as a novel therapeutic target to prevent end-organ damage associated with hypertension.

Abstract 152: Mitochondrial Fission Inhibitor Mdivi-1 Attenuates Angiotensin II-Induced Cardiovascular Remodeling

Mitochondrial dysfunction has been implicated in various types of cardiovascular diseases which may involve overload and de-compensation in mitochondrial quality/quantity control. However, limited mechanistic insight is available regarding the contribution and mechanism of mitochondrial quality control in hypertension. In the present study, we tested our hypothesis that enhancement of mitochondrial fission in vascular cells is involved in hypertensive vascular remodeling. 8 week old male C57/Bl6 mice were infused with angiotensin II (1000 ng/kg/min) for 2 weeks with or without treatment of mitochondrial fission inhibitor Mdivi-1 (25 mg/kg ip every other day). Mdivi-1 significantly inhibited AngII-induced left ventricular hypertrophy assessed by heart weight body weight ratio as well as by echocardiogram. Histological assessment of the Mdivi-1-treated mouse hearts further demonstrated significant suppression of vessel hypertrophy and fibrosis induced by AngII. However, Mdivi-1 did not affect heart rate or hypertension induced by AngII assessed by telemetry. KDEL and VCAM1 staining of the heart and aorta suggest attenuation of vascular ER stress and inflammation, respectively. In cultured rat vascular smooth muscle cell (VSMCs), AngII induced mitochondrial fission promoting Drp1 phosphorylation at Ser616 and Ser637. Pretreatment of Mdivi-1 (5 microM 30 min) attenuated 100 nM AngII-induced mitochondrial fission in VSMCs assessed by mito-tracker staining. Mdivi-1 also attenuated extracellular collagen accumulation induced by AngII in VSMCs assessed by Sirius Red staining quantification kit. In conclusion, this data suggests that Mdivi-1 treatment prevents AngII-induced cardiovascular remodeling independently of hypertension via suppression of mitochondrial fission and attenuation of ER stress and inflammation in target organs.

Abstract 9: Involvement of Caveolin-1 in Vascular Remodeling and Inflammation Induced by Angiotensin II

We have recently reported that caveolin-1 (Cav1) enriched membrane microdomains in vascular smooth muscle cells (VSMC) mediate a metalloprotease ADAM17-dependent EGF receptor (EGFR) transactivation, which is linked to vascular remodeling induced by AngII. We have tested our hypothesis that Cav1, a major structural protein of caveolae, plays a critical role for development of vascular remodeling by AngII via regulation of ADAM17 and EGFR. Here, 8 week old male Cav1-/- and control Cav+/+ wild-type mice (WT) were infused with AngII (1 μg/kg/min) for 2 weeks to induce vascular remodeling and hypertension. Upon AngII infusion, histological assessments demonstrated medial hypertrophy and perivascular fibrosis of coronary and renal arteries in WT mice compared with saline-infused control mice. The AngII-infused WT mice also showed a phenotype of cardiac hypertrophy with increased HW/BW ratio (mg/g: 8.0±0.6 vs 5.7±0.7 p<0.01) compared with WT control. In contrast to AngII-infused WT mice, Cav1-/- mice with AngII showed attenuation of vascular remodeling but not cardiac hypertrophy ; HW/BW ratio (8.6±0.5 vs 6.4±0.2 p<0.05). Similar levels of AngII-induced hypertension were observed in both WT and Cav1-/- mice assessed by telemetry (MAP mmHg: 142±9 vs 154±20). In WT mice, Ang II enhanced ADAM17 expression and phospho-Tyr EGFR staining in heart and kidney vasculature. These events were attenuated in vessels from Cav1-/- mice infused with AngII. In addition, IHC analysis revealed less ER stress in heart and kidney vasculature of AngII-infused Cav1-/- mice compared with WT mice. Enhanced Cav1 and VCAM-1 expression were also observed in the aorta from AngII-infused WT mice but not in Cav1-/- aorta. These data suggest that Cav1 and presumably vascular caveolae play critical roles for vascular remodeling and inflammation via induction of ADAM17 and activation of EGFR independent of blood pressure or cardiac hypertrophy regulation.

Epidermal Growth Factor Receptor Transactivation: Mechanisms, Pathophysiology, and Potential Therapies in the Cardiovascular System

Epidermal growth factor receptor (EGFR) activation impacts the physiology and pathophysiology of the cardiovascular system, and inhibition of EGFR activity is emerging as a potential therapeutic strategy to treat diseases including hypertension, cardiac hypertrophy, renal fibrosis, and abdominal aortic aneurysm. The capacity of G protein-coupled receptor (GPCR) agonists, such as angiotensin II (AngII), to promote EGFR signaling is called transactivation and is well described, yet delineating the molecular processes and functional relevance of this crosstalk has been challenging. Moreover, these critical findings are dispersed among many different fields. The aim of our review is to highlight recent advancements in defining the signaling cascades and downstream consequences of EGFR transactivation in the cardiovascular renal system. We also focus on studies that link EGFR transactivation to animal models of the disease, and we discuss potential therapeutic applications.

Effect of Interleukin-10 and Laminar Shear Stress on Endothelial Nitric Oxide Synthase and Nitric Oxide in African American Human Umbilical Vein Endothelial Cells

BACKGROUND

African Americans have a predisposition to heightened systemic inflammation and a high prevalence of hypertension.

OBJECTIVE

The purpose of this study was to evaluate the influence of interleukin-10 (IL-10) and laminar shear stress (LSS) on African American endothelial cells by measuring total endothelial nitric oxide synthase (eNOS) protein expression and its phosphorylated form (p-eNOS) at Serine 1177, and nitric oxide (NO) levels, in response to IL-10 incubation and high physiological levels of LSS, used as an in vitro mimetic for aerobic exercise training (AEXT).

DESIGN

Human umbilical vein endothelial cells (HUVEC) from an African American donor were cultured. The experimental conditions included Static, Static with IL-10 Incubation, LSS at 20 dynes/cm², and LSS at 20 dynes/cm² with IL-10 Incubation. Western blotting was used to measure eNOS and p-eNOS protein expression in the cells. A modified Griess assay was used to measure NO metabolites in the cell culture media.

RESULTS

There were significant increases in p-eNOS, eNOS, and NO in the LSS at 20 dynes/cm² and LSS at 20 dynes/cm² with IL-10 Incubation experimental conditions when compared to the Static experimental condition. There were no other statistically significant differences demonstrating that IL-10 did not have an additive effect on eNOS activity in our study.

CONCLUSION

The significant increases in p-eNOS, eNOS, and NO as a result of LSS in African American HUVECs suggest that AEXT may be a viable, nonpharmacologic method to improve vascular inflammation status and vasodilation, and thereby contribute to hypertension reduction in the African American population.

Abstract P108: Caveolin-1 is Required for Vascular Remodeling Induced by Angiotensin Ii

We have recently reported that caveolin-1 (Cav1) enriched membrane microdomains in vascular smooth muscle cells (VSMC) mediates a metalloprotease ADAM17-dependent EGF receptor (EGFR) transactivation, which is linked to vascular remodeling induced by AngII. We have tested our hypothesis that Cav1, a major structural protein of caveolae, plays a critical role in AngII-mediated vascular remodeling via regulation of ADAM17 and EGFR. 8 week old male Cav1-/- and control Cav+/+ wild-type mice (WT) were infused with AngII (1 μg/kg/min) for 2 weeks to induce vascular remodeling and hypertension. Upon AngII infusion, histological assessments demonstrated medial hypertrophy and perivascular fibrosis of coronary and renal arteries in WT mice compared to sham-operated mice. The AngII-infused WT mice also showed a phenotype of cardiac hypertrophy with increased HW/BW ratio (mg/g: 8.0±0.6 vs 5.7±0.7 p<0.01) compared with sham-operated WT control. In contrast, vascular remodeling but not cardiac hypertrophy were attenuated in Cav1-/- mice with AngII infusion; HW/BW ratio (8.6±0.5 vs 6.4±0.2 p<0.05) compared to sham-operated mice. However, AngII induced similar levels of hypertension in both WT and Cav1-/- mice as assessed by telemetry (MAP mmHg: 142±9 vs 154±20). AngII infusion in WT mice enhanced ADAM17 and phospho-Tyr EGFR staining in heart and kidney vasculature, whereas AngII-infused Cav1-/- mice showed diminished ADAM17 and phospho-Tyr EGFR staining within the vasculature. In addition, IHC analyses revealed reduced vascular ER stress in heart and kidney samples of AngII-infused Cav1-/- mice compared to WT mice. Expression of Cav1 was predominantly observed within the endothelium and was enhanced upon AngII infusion in WT mice. These data suggest that Cav1, and presumably endothelial caveolae microdomains, plays a critical role in vascular remodeling via vascular induction of ADAM17 and activation of EGFR independent of blood pressure or cardiac hypertrophy regulation.

Regulation of Renal Hemodynamics and Function by RGS2

Regulator of G protein signaling 2 (RGS2) controls G protein coupled receptor (GPCR) signaling by acting as a GTPase-activating protein for heterotrimeric G proteins. Certain Rgs2 gene mutations have been linked to human hypertension. Renal RGS2 deficiency is sufficient to cause hypertension in mice; however, the pathological mechanisms are unknown. Here we determined how the loss of RGS2 affects renal function. We examined renal hemodynamics and tubular function by monitoring renal blood flow (RBF), glomerular filtration rate (GFR), epithelial sodium channel (ENaC) expression and localization, and pressure natriuresis in wild type (WT) and RGS2 null (RGS2-/-) mice. Pressure natriuresis was determined by stepwise increases in renal perfusion pressure (RPP) and blood flow, or by systemic blockade of nitric oxide synthase with L-NG-Nitroarginine methyl ester (L-NAME). Baseline GFR was markedly decreased in RGS2-/- mice compared to WT controls (5.0 ± 0.8 vs. 2.5 ± 0.1 μl/min/g body weight, p<0.01). RBF was reduced (35.4 ± 3.6 vs. 29.1 ± 2.1 μl/min/g body weight, p=0.08) while renal vascular resistance (RVR; 2.1 ± 0.2 vs. 3.0 ± 0.2 mmHg/μl/min/g body weight, p<0.01) was elevated in RGS2-/- compared to WT mice. RGS2 deficiency caused decreased sensitivity and magnitude of changes in RVR and RBF after a step increase in RPP. The acute pressure–natriuresis curve was shifted rightward in RGS2-/- relative to WT mice. Sodium excretion rate following increased RPP by L-NAME was markedly decreased in RGS2-/- mice and accompanied by increased translocation of ENaC to the luminal wall. We conclude that RGS2 deficiency impairs renal function and autoregulation by increasing renal vascular resistance and reducing renal blood flow. These changes impair renal sodium handling by favoring sodium retention. The findings provide a new line of evidence for renal dysfunction as a primary cause of hypertension.

Role of epidermal growth factor receptor and endoplasmic reticulum stress in vascular remodeling induced by angiotensin II

The mechanisms by which angiotensin II (AngII) elevates blood pressure and enhances end-organ damage seem to be distinct. However, the signal transduction cascade by which AngII specifically mediates vascular remodeling such as medial hypertrophy and perivascular fibrosis remains incomplete. We have previously shown that AngII-induced epidermal growth factor receptor (EGFR) transactivation is mediated by disintegrin and metalloproteinase domain 17 (ADAM17), and that this signaling is required for vascular smooth muscle cell hypertrophy but not for contractile signaling in response to AngII. Recent studies have implicated endoplasmic reticulum (ER) stress in hypertension. Interestingly, EGFR is capable of inducing ER stress. The aim of this study was to test the hypothesis that activation of EGFR and ER stress are critical components required for vascular remodeling but not hypertension induced by AngII. Mice were infused with AngII for 2 weeks with or without treatment of EGFR inhibitor, erlotinib, or ER chaperone, 4-phenylbutyrate. AngII infusion induced vascular medial hypertrophy in the heart, kidney and aorta, and perivascular fibrosis in heart and kidney, cardiac hypertrophy, and hypertension. Treatment with erlotinib as well as 4-phenylbutyrate attenuated vascular remodeling and cardiac hypertrophy but not hypertension. In addition, AngII infusion enhanced ADAM17 expression, EGFR activation, and ER/oxidative stress in the vasculature, which were diminished in both erlotinib-treated and 4-phenylbutyrate-treated mice. ADAM17 induction and EGFR activation by AngII in vascular cells were also prevented by inhibition of EGFR or ER stress. In conclusion, AngII induces vascular remodeling by EGFR activation and ER stress via a signaling mechanism involving ADAM17 induction independent of hypertension.

Bioinformatic identification of connective tissue growth factor as an osteogenic protein within skeletal muscle

Aging is associated with increasing incidence of osteoporosis; a skeletal disorder characterized by compromised bone strength that may predispose patients to an increased risk of fracture. It is imperative to identify novel ways in which to attenuate such declines in the functional properties of bone. The purpose of this study was to identify, through in silico, in vitro, and in vivo approaches, a protein secreted from skeletal muscle that is putatively involved in bone formation. We performed a functional annotation bioinformatic analysis of human skeletal muscle‐derived secretomes (n = 319) using DAVID software. Cross‐referencing was conducted using OMIM, Unigene, UniProt, GEO, and CGAP databases. Signal peptides and transmembrane residues were analyzed using SignalP and TMHMM software. To further investigate functionality of the identified protein, L6 and C2C12 myotubes were grown for in vitro analysis. C2C12 myotubes were subjected to 16 h of glucose deprivation (GD) prior to analysis. In vivo experiments included analysis of 6‐week calorie restricted (CR) rat muscle samples. Bioinformatic analysis yielded 15 genes of interest. GEO dataset analysis identified BMP5, COL1A2, CTGF, MGP, MMP2, and SPARC as potential targets for further processing. Following TMHMM and SignalP processing, CTGF was chosen as a candidate gene. CTGF expression level was increased during L6 myoblast differentiation (P <0.01). C2C12 myotubes showed no change in response to GD. Rat soleus muscle samples exhibited an increase in CTGF expression (n = 16) in response to CR (35%) (P <0.05). CTGF was identified as a skeletal muscle expressed protein through bioinformatic analysis of skeletal muscle‐derived secretomes and in vitro/in vivo analysis. Future study is needed to determine the role of muscle‐derived CTGF in bone formation and remodeling processes.

In this study, we explore the method of bioinformatic analysis, coupled with in vitro and in vivo investigation, to identify a new skeletal muscle‐derived protein with osteogenic properties. CTGF is expressed in young, healthy skeletal muscle, and this expression is increased with calorie restriction. Muscular secretion of CTGF might play an osteogenic role in maintaining bone health.