IU Indianapolis ScholarWorks :: Browsing by Author "Atkinson, Simon J."

Browsing by Author "Atkinson, Simon J."

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ADF/Cofilin Activation Regulates Actin Polymerization and Tension Development in Canine Tracheal Smooth Muscle
(2009-09-03T15:28:09Z) Zhao, Rong; Gunst, Susan J.; Atkinson, Simon J.; Elmendorf, Jeffrey S.; Sturek, Michael S.
The contractile activation of airway smooth muscle tissues stimulates actin polymerization and the inhibition of actin polymerization inhibits tension development. Actin depolymerizing factor (ADF) and cofilin are members of a family of actin–binding proteins that mediate the severing of F–actin when activated by dephosphorylation at serine 3. The role of ADF/cofilin activation in the regulation of actin dynamics and tension development during the contractile activation of airway smooth was evaluated in intact canine tracheal smooth muscle tissues. Two–dimensional gel electrophoresis revealed that ADF and cofilin exist in similar proportions in the muscle tissues and that approximately 40% of the total ADF/cofilin in unstimulated tissues is phosphorylated (inactivated). Phospho–ADF/cofilin decreased concurrently with tension development in response to stimulation with acetylcholine (ACh) or potassium depolarization indicating the activation of ADF/cofilin. Expression of an inactive phospho–cofilin mimetic (cofilin S3E), but not WT cofilin in the smooth muscle tissues inhibited endogenous ADF/cofilin dephosphorylation and ACh–induced actin polymerization. Expression of cofilin S3E in the tissues depressed tension development in response to ACh, but it did not affect myosin light chain phosphorylation. The ACh–induced dephosphorylation of ADF/cofilin required the Ca2+–dependent activation of calcineurin (PP2B). Expression of Slingshot (SSH) inactive phosphatase (C393S) decreased force development and cofilin dephosphorylation. Activation of ADF/cofilin was also required for the relaxation of tracheal muscle tissues induced by forskolin and isoproterenol. Cofilin activation in response to forskolin was not Ca2+–dependent and was not inhibited by calcineurin inhibitors, suggesting it was regulated by a different mechanism. Cofilin activation is required for actin dynamics and tension development in response to the contractile stimulation of tracheal smooth muscle and is regulated by both contractile and relaxing stimuli. These concepts are critical to understanding the mechanisms of smooth muscle contraction and relaxation, which may provide novel targets for therapeutic intervention in the treatment of abnormal airway responsiveness.
Dishevelled-associated activator of morphogenesis 1 (Daam1) is required for heart morphogenesis
(2011-01) Li, Deqiang; Hallett, Mark A.; Zhu, Wuqiang; Rubart, Michael; Liu, Ying; Yang, Zhenyun; Chen, Hanying; Haneline, Laura S.; Chan, Rebecca J.; Schwartz, Robert J.; Field, Loren J.; Atkinson, Simon J.; Shou, Weinian
Dishevelled-associated activator of morphogenesis 1 (Daam1), a member of the formin protein family, plays an important role in regulating the actin cytoskeleton via mediation of linear actin assembly. Previous functional studies of Daam1 in lower species suggest its essential role in Drosophila trachea formation and Xenopus gastrulation. However, its in vivo physiological function in mammalian systems is largely unknown. We have generated Daam1-deficient mice via gene-trap technology and found that Daam1 is highly expressed in developing murine organs, including the heart. Daam1-deficient mice exhibit embryonic and neonatal lethality and suffer multiple cardiac defects, including ventricular noncompaction, double outlet right ventricles and ventricular septal defects. In vivo genetic rescue experiments further confirm that the lethality of Daam1-deficient mice results from the inherent cardiac abnormalities. In-depth analyses have revealed that Daam1 is important for regulating filamentous actin assembly and organization, and consequently for cytoskeletal function in cardiomyocytes, which contributes to proper heart morphogenesis. Daam1 is also found to be important for proper cytoskeletal architecture and functionalities in embryonic fibroblasts. Biochemical analyses indicate that Daam1 does not regulate cytoskeletal organization through RhoA, Rac1 or Cdc42. Our study highlights a crucial role for Daam1 in regulating the actin cytoskeleton and tissue morphogenesis.
Exogenous Gene Transmission of Isocitrate Dehydrogenase 2 Mimics Ischemic Preconditioning Protection
(American Society of Nephrology, 2018-04) Kolb, Alexander L.; Corridon, Peter R.; Zhang, Shijun; Xu, Weimin; Witzmann, Frank A.; Collett, Jason A.; Rhodes, George J.; Winfree, Seth; Bready, Devin; Pfeffenberger, Zechariah J.; Pomerantz, Jeremy M.; Hato, Takashi; Nagami, Glenn T.; Molitoris, Bruce A.; Basile, David P.; Atkinson, Simon J.; Bacallao, Robert L.; Biology, School of Science
Ischemic preconditioning confers organ-wide protection against subsequent ischemic stress. A substantial body of evidence underscores the importance of mitochondria adaptation as a critical component of cell protection from ischemia. To identify changes in mitochondria protein expression in response to ischemic preconditioning, we isolated mitochondria from ischemic preconditioned kidneys and sham-treated kidneys as a basis for comparison. The proteomic screen identified highly upregulated proteins, including NADP+-dependent isocitrate dehydrogenase 2 (IDH2), and we confirmed the ability of this protein to confer cellular protection from injury in murine S3 proximal tubule cells subjected to hypoxia. To further evaluate the role of IDH2 in cell protection, we performed detailed analysis of the effects of Idh2 gene delivery on kidney susceptibility to ischemia-reperfusion injury. Gene delivery of IDH2 before injury attenuated the injury-induced rise in serum creatinine (P<0.05) observed in controls and increased the mitochondria membrane potential (P<0.05), maximal respiratory capacity (P<0.05), and intracellular ATP levels (P<0.05) above those in controls. This communication shows that gene delivery of Idh2 can confer organ-wide protection against subsequent ischemia-reperfusion injury and mimics ischemic preconditioning.
Functional studies of the kidney of living animals using multicolor 2-photon microscopy
(2002-09) Dunn, Kenneth W.; Sandoval, Ruben M.; Kelly, Katherine J.; Dagher, Pierre C.; Tanner, George A.; Atkinson, Simon J.; Bacallao, Robert L.; Molitoris, Bruce A.
Optical microscopy, when applied to living animals, provides a powerful means of studying cell biology in the most physiologically relevant setting. The ability of two-photon microscopy to collect optical sections deep into biological tissues has opened up the field of intravital microscopy to high-resolution studies of the brain, lens, skin, and tumors. Here we present examples of the way in which two-photon microscopy can be applied to intravital studies of kidney physiology. Because the kidney is easily externalized without compromising its function, microscopy can be used to evaluate various aspects of renal function in vivo. These include cell vitality and apoptosis, fluid transport, receptor-mediated endocytosis, blood flow, and leukocyte trafficking. Efficient two-photon excitation of multiple fluorophores permits comparison of multiple probes and simultaneous characterization of multiple parameters and yields spectral information that is crucial to the interpretation of images containing uncharacterized autofluorescence. The studies described here demonstrate the way in which two-photon microscopy can provide a level of resolution previously unattainable in intravital microscopy, enabling kinetic analyses and physiological studies of the organs of living animals with subcellular resolution.
Hydrodynamic Isotonic Fluid Delivery Ameliorates Moderate-to-Severe Ischemia-Reperfusion Injury in Rat Kidneys
(American Society of Nephrology, 2017-07) Collett, Jason A.; Corridon, Peter R.; Mehrotra, Purvi; Kolb, Alexander L.; Rhodes, George J.; Miller, Caroline A.; Molitoris, Bruce A.; Pennington, Janice G.; Sandoval, Ruben M.; Atkinson, Simon J.; Campos-Bilderback, Silvia B.; Basile, David P.; Bacallao, Robert L.; Cellular and Integrative Physiology, School of Medicine
Highly aerobic organs like the kidney are innately susceptible to ischemia-reperfusion (I/R) injury, which can originate from sources including myocardial infarction, renal trauma, and transplant. Therapy is mainly supportive and depends on the cause(s) of damage. In the absence of hypervolemia, intravenous fluid delivery is frequently the first course of treatment but does not reverse established AKI. Evidence suggests that disrupting leukocyte adhesion may prevent the impairment of renal microvascular perfusion and the heightened inflammatory response that exacerbate ischemic renal injury. We investigated the therapeutic potential of hydrodynamic isotonic fluid delivery (HIFD) to the left renal vein 24 hours after inducing moderate-to-severe unilateral IRI in rats. HIFD significantly increased hydrostatic pressure within the renal vein. When conducted after established AKI, 24 hours after I/R injury, HIFD produced substantial and statistically significant decreases in serum creatinine levels compared with levels in animals given an equivalent volume of saline via peripheral infusion (P<0.05). Intravital confocal microscopy performed immediately after HIFD showed improved microvascular perfusion. Notably, HIFD also resulted in immediate enhancement of parenchymal labeling with the fluorescent dye Hoechst 33342. HIFD also associated with a significant reduction in the accumulation of renal leukocytes, including proinflammatory T cells. Additionally, HIFD significantly reduced peritubular capillary erythrocyte congestion and improved histologic scores of tubular injury 4 days after IRI. Taken together, these results indicate that HIFD performed after establishment of AKI rapidly restores microvascular perfusion and small molecule accessibility, with improvement in overall renal function.
Indiana O’Brien Center for Advanced Microscopic Analysis
(Office of the Vice Chancellor for Research, 2014-04-11) Atkinson, Simon J.; Dunn, Kenneth W.; Kamocka, Malgorzata; Molitoris, Bruce A.
In June 2002, the IU Division of Nephrology received NIH funding to establish a George M. O'Brien Center for Advanced Renal Microscopic Analysis at the Indiana Center for Biological Microscopy. The primary goal of this Center is to develop new optical methodologies for investigators in Nephrologic and Urologic Research and to make the technology widely accessible to the renal research community. Approaches include intravital multiphoton microscopy, 3-dimensional imaging and quantitative microscopic analysis. We have established the Indiana O’Brien Fellows Program, which provides funds for investigators to implement these new techniques for their specific research needs, either in their laboratories, or utilizing the facilities of the Center.
Ischemic preconditioning and hydrodynamic delivery for the prevention of acute kidney injury
(2015-07) Lu, Keyin; Atkinson, Simon J.; Bacallao, Robert L.; Blazer-Yost, Bonnie
Acute Kidney Injury (AKI) is a prevalent and significant problem whose primary treatment is supportive care. Ischemic preconditioning is a strategy used to protect organs from ischemic injury via a prior injury. Ischemic preconditioning in the kidneys has been shown to confer protection onto kidneys from subsequent ischemic insults with attenuated serum creatinine values in treated rats. In the preconditioned kidneys, the enzyme IDH2 was discovered to be upregulated in the mitochondria. Hydrodynamic fluid delivery to the kidney was found to be a viable technique for delivering this gene to the kidney, resulting in artificially upregulated expression of IDH2. Via a two-pronged effort to discern the functional significance of ischemic preconditioning and hydrodynamic IDH2 fluid injections, we performed mitochondrial oxygen respiration assays on both preconditioned and injected kidneys. We found that renal ischemic preconditioning resulted in no significant difference between sham and preconditioned, subsequently injured kidneys, which is similar to the results from the serum creatinine studies. Hydrodynamically IDH2-injected, and subsequently injured kidneys respire significantly better than vehicle injected, and subsequently injured kidneys, which shows that hydrodynamic injections of IDH2 protects kidneys against injury, and partially mimics the effects of preconditioning.
Kidney surveillance in the spotlight: contrast-induced acute kidney injury illuminated
(American Society for Clinical Investigation, 2018-07-02) Atkinson, Simon J.; Biology, School of Science
Acute kidney injury comprises a heterogeneous group of conditions characterized by a sudden decrease in renal function over hours to days. Contrast-induced acute kidney injury (CI-AKI) is caused by radiographic contrast agents used in diagnostic imaging. In the current issue of the JCI, Lau et al. use a mouse model of CI-AKI to study the role of resident and infiltrating phagocytes, recruited leukocytes, and tubular cells in the immune surveillance response to contrast agents. This study has the potential to provide innovative therapies for human CI-AKI.
Mechanisms of Cytoskeletal Dysregulation in the Kidney Proximal Tubule During ATP Depletion and Ischemia
(2009-08) Zhang, Hao; Atkinson, Simon J.; Harrington, Maureen A.; Marrs, James A.; Quilliam, Lawrence A.
Knowledge of the molecular and cellular mechanisms of ischemic injury is necessary for understanding acute kidney injury and devising optimal treatment regimens. The cortical actin cytoskeleton in the proximal tubule epithelial cells of the kidney nephron, playing an important role in both the establishment and maintenance of cell polarity, is drastically disrupted by the onset of ischemia. We found that in LLC-PK cells (a porcine kidney proximal tubule epithelial cell line), cortactin, an important regulator of actin assembly and organization, translocated from the cell cortex to the cytoplasmic regions upon ischemia/ATP-depletion. Meanwhile both the tyrosine phosphorylation level of cortactin and cortactin’s interaction with either F-actin or the actin nucleator Arp2/3 complex were down-regulated upon ischemia/ATP-depletion or inhibition of Src kinase activity. These results suggest that tyrosine phosphorylation plays an important role in regulating cortactin’s cellular function and localization in the scenario of kidney ischemia. The Rho GTPase signaling pathways is also a critical mediator of the effects of ATP depletion and ischemia on the actin cytoskeleton, but the mechanism by which ATP depletion leads to altered RhoA and Rac1 activity is unknown. We propose that ischemia and ATP depletion result in activation of AMP-activated protein kinase (AMPK) and that this affects Rho GTPase activity and cytoskeletal organization (possibly via TSC1/2 complex and/or mTOR complex). We found that AMPK was rapidly activated (≤5 minutes) by ATP depletion in S3 epithelial cells derived from the proximal tubule in mouse kidney, and there was a corresponding decrease in RhoA and Rac1 activity. During graded ATP-depletion, we found intermediate levels of AMPK activity at the intermediate ATP levels, and that the activity of RhoA and Rac1 activity correlated inversely with the activity of AMPK. Activation of AMPK using two different drugs suppressed RhoA activity, and also led to morphological changes of stress fibers. In addition, the inhibition of AMPK activation partially rescued the disruption of stress fibers caused by ATP-depletion. This evidence supports our hypothesis that the activation of AMPK is upstream of the signaling pathways that eventually lead to RhoA inactivation and cytoskeletal dysregulation during ATP-depletion.
O’ Brien Center
(Office of the Vice Chancellor for Research, 2013-04-05) Atkinson, Simon J.; Dunn, Kenneth W.; Molitoris, Bruce A.
The O’Brien Center for Advanced Renal Microscopy and Analysis is based around the Indiana Center for Biological Microscopy in Indianapolis (ICBM), and is supported by partnerships with Purdue University and the University of North Carolina. The Center acts as a national resource for investigators to apply state-of-the-art techniques in fluorescence microscopy to research in kidney biology and pathophysiology. Investigators have access to four microscope systems capable of multiphoton and confocal imaging and optimized for intravital imaging studies on rodents. Point-scanning and spinning-disk confocal systems are also available. Training and assistance with development of imaging protocols are available from expert staff at the ICBM. The Center emphasizes development of new and improved methods for imaging the kidney and seeks to disseminate these innovations as widely as possible amongst renal investigators. Currently, the Center is (1) developing new software for rendering, segmentation, analysis and stabilization of three-dimensional data from live imaging experiments; (2) developing new fluorescent probes and delivery methods optimized for intravital imaging studies in the kidney; and (3) exploring methods to increase the reach of multiphoton imaging in the kidney. Funding is available through the Center’s O’Brien Fellows Program to support short visits (one-two weeks) to Indianapolis for data collection, development of imaging protocols to address particular questions and for training in fluorescence microscopy and image analysis. The Center also offers instructional workshops in fluorescence microscopy and intravital imaging every two years. Current information about how to access the resources available through the Center is available at http://medicine.iupui.edu/nephrology/obrien.

Browsing by Author "Atkinson, Simon J."

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