S. Sriramula | Louisiana State University Health Sciences Center in New Orleans (original) (raw)
Papers by S. Sriramula
American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 2014
Hypertension, 2014
Overactivity of the renin-angiotensin system, oxidative stress, and cyclooxygenases (COX) in the ... more Overactivity of the renin-angiotensin system, oxidative stress, and cyclooxygenases (COX) in the brain are implicated in the pathogenesis of hypertension. We previously reported that angiotensin-converting enzyme 2 (ACE2) overexpression in the brain attenuates the development of deoxycorticosterone acetate-salt hypertension, a neurogenic hypertension model with enhanced brain renin-angiotensin system and sympathetic activity. To elucidate the mechanisms involved, we investigated whether oxidative stress, mitogen-activated protein kinase signaling and cyclooxygenase (COX) activation in the brain are modulated by ACE2 in neurogenic hypertension. Deoxycorticosterone acetate-salt hypertension significantly increased expression of Nox-2 (+61±5%), Nox-4 (+50±13%), and nitrotyrosine (+89±32%) and reduced activity of the antioxidant enzymes, catalase (-29±4%) and superoxide dismutase (-31±7%), indicating increased oxidative stress in the brain of nontransgenic mice. This increased oxidative stress was attenuated in transgenic mice overexpressing ACE2 in the brain. Deoxycorticosterone acetate-salt-induced reduction of neuronal nitric oxide synthase expression (-26±7%) and phosphorylated endothelial nitric oxide synthase/total endothelial nitric oxide synthase (-30±3%), and enhanced phosphorylation of protein kinase B and extracellular signal-regulated kinase 1/2 in the paraventricular nucleus, were reversed by ACE2 overexpression. In addition, ACE2 overexpression blunted the hypertension-mediated increase in gene and protein expression of COX-1 and COX-2 in the paraventricular nucleus. Furthermore, gene silencing of either COX-1 or COX-2 in the brain, reduced microglial activation and accompanied neuroinflammation, ultimately attenuating Deoxycorticosterone acetate-salt hypertension. Together, these data provide evidence that brain ACE2 overexpression reduces oxidative stress and COX-mediated neuroinflammation, improves antioxidant and nitric oxide signaling, and thereby attenuates the development of neurogenic hypertension.
Circulation Research, 2013
Overactivity of the brain renin-angiotensin system is a major contributor to neurogenic hypertens... more Overactivity of the brain renin-angiotensin system is a major contributor to neurogenic hypertension. Although overexpression of angiotensin-converting enzyme type 2 (ACE2) has been shown to be beneficial in reducing hypertension by transforming angiotensin II into angiotensin-(1-7), several groups have reported decreased brain ACE2 expression and activity during the development of hypertension. We hypothesized that ADAM17-mediated ACE2 shedding results in decreased membrane-bound ACE2 in the brain, thus promoting the development of neurogenic hypertension. To test this hypothesis, we used the deoxycorticosterone acetate-salt model of neurogenic hypertension in nontransgenic and syn-hACE2 mice overexpressing ACE2 in neurons. Deoxycorticosterone acetate-salt treatment in nontransgenic mice led to significant increases in blood pressure, hypothalamic angiotensin II levels, inflammation, impaired baroreflex sensitivity, and autonomic dysfunction, as well as decreased hypothalamic ACE2 activity and expression, although these changes were blunted or prevented in syn-hACE2 mice. In addition, reduction of ACE2 expression and activity in the brain paralleled an increase in ACE2 activity in the cerebrospinal fluid of nontransgenic mice after deoxycorticosterone acetate-salt treatment and were accompanied by enhanced ADAM17 expression and activity in the hypothalamus. Chronic knockdown of ADAM17 in the brain blunted the development of hypertension and restored ACE2 activity and baroreflex function. Our data provide the first evidence that ADAM17-mediated shedding impairs brain ACE2 compensatory activity, thus contributing to the development of neurogenic hypertension.
Cardiovascular Research, 2010
Cardiovascular Research, 2011
AJP: Regulatory, Integrative and Comparative Physiology, 2011
AJP: Regulatory, Integrative and Comparative Physiology, 2011
Angiotensin-converting enzyme 2 (ACE2) is a component of the renin-angiotensin system, and its ex... more Angiotensin-converting enzyme 2 (ACE2) is a component of the renin-angiotensin system, and its expression and activity have been shown to be reduced in cardiovascular diseases. Enzymatic activity of ACE2 is commonly measured by hydrolysis of quenched fluorescent substrates in the absence or presence of an ACE2-specific inhibitor, such as the commercially available inhibitor DX600. Whereas recombinant human ACE2 is readily detected in mouse tissues using 1 μM DX600 at pH 7.5, the endogenous ACE2 activity in mouse tissues is barely detectable. We compared human, mouse, and rat ACE2 overexpressed in cell lines for their sensitivity to inhibition by DX600. ACE2 from all three species could be inhibited by DX600, but the half maximal inhibitory concentration (IC(50)) for human ACE2 was much lower (78-fold) than for rodent ACE2. Following optimization of pH, substrate concentration, and antagonist concentration, rat and mouse ACE2 expressed in a cell line could be accurately quantified with 10 μM DX600 (>95% inhibition) but not with 1 μM DX600 (<75% inhibition). Validation that the optimized method robustly quantifies ACE2 in mouse tissues (kidney, brain, heart, and plasma) was performed using wild-type and ACE2 knockout mice. This study provides a reliable method for measuring human, as well as endogenous ACE2 activity in rodents. Our data underscore the importance of validating the effect of DX600 on ACE2 from each particular species at the experimental conditions employed.
AJP: Heart and Circulatory Physiology, 2007
American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 2014
Hypertension, 2014
Overactivity of the renin-angiotensin system, oxidative stress, and cyclooxygenases (COX) in the ... more Overactivity of the renin-angiotensin system, oxidative stress, and cyclooxygenases (COX) in the brain are implicated in the pathogenesis of hypertension. We previously reported that angiotensin-converting enzyme 2 (ACE2) overexpression in the brain attenuates the development of deoxycorticosterone acetate-salt hypertension, a neurogenic hypertension model with enhanced brain renin-angiotensin system and sympathetic activity. To elucidate the mechanisms involved, we investigated whether oxidative stress, mitogen-activated protein kinase signaling and cyclooxygenase (COX) activation in the brain are modulated by ACE2 in neurogenic hypertension. Deoxycorticosterone acetate-salt hypertension significantly increased expression of Nox-2 (+61±5%), Nox-4 (+50±13%), and nitrotyrosine (+89±32%) and reduced activity of the antioxidant enzymes, catalase (-29±4%) and superoxide dismutase (-31±7%), indicating increased oxidative stress in the brain of nontransgenic mice. This increased oxidative stress was attenuated in transgenic mice overexpressing ACE2 in the brain. Deoxycorticosterone acetate-salt-induced reduction of neuronal nitric oxide synthase expression (-26±7%) and phosphorylated endothelial nitric oxide synthase/total endothelial nitric oxide synthase (-30±3%), and enhanced phosphorylation of protein kinase B and extracellular signal-regulated kinase 1/2 in the paraventricular nucleus, were reversed by ACE2 overexpression. In addition, ACE2 overexpression blunted the hypertension-mediated increase in gene and protein expression of COX-1 and COX-2 in the paraventricular nucleus. Furthermore, gene silencing of either COX-1 or COX-2 in the brain, reduced microglial activation and accompanied neuroinflammation, ultimately attenuating Deoxycorticosterone acetate-salt hypertension. Together, these data provide evidence that brain ACE2 overexpression reduces oxidative stress and COX-mediated neuroinflammation, improves antioxidant and nitric oxide signaling, and thereby attenuates the development of neurogenic hypertension.
Circulation Research, 2013
Overactivity of the brain renin-angiotensin system is a major contributor to neurogenic hypertens... more Overactivity of the brain renin-angiotensin system is a major contributor to neurogenic hypertension. Although overexpression of angiotensin-converting enzyme type 2 (ACE2) has been shown to be beneficial in reducing hypertension by transforming angiotensin II into angiotensin-(1-7), several groups have reported decreased brain ACE2 expression and activity during the development of hypertension. We hypothesized that ADAM17-mediated ACE2 shedding results in decreased membrane-bound ACE2 in the brain, thus promoting the development of neurogenic hypertension. To test this hypothesis, we used the deoxycorticosterone acetate-salt model of neurogenic hypertension in nontransgenic and syn-hACE2 mice overexpressing ACE2 in neurons. Deoxycorticosterone acetate-salt treatment in nontransgenic mice led to significant increases in blood pressure, hypothalamic angiotensin II levels, inflammation, impaired baroreflex sensitivity, and autonomic dysfunction, as well as decreased hypothalamic ACE2 activity and expression, although these changes were blunted or prevented in syn-hACE2 mice. In addition, reduction of ACE2 expression and activity in the brain paralleled an increase in ACE2 activity in the cerebrospinal fluid of nontransgenic mice after deoxycorticosterone acetate-salt treatment and were accompanied by enhanced ADAM17 expression and activity in the hypothalamus. Chronic knockdown of ADAM17 in the brain blunted the development of hypertension and restored ACE2 activity and baroreflex function. Our data provide the first evidence that ADAM17-mediated shedding impairs brain ACE2 compensatory activity, thus contributing to the development of neurogenic hypertension.
Cardiovascular Research, 2010
Cardiovascular Research, 2011
AJP: Regulatory, Integrative and Comparative Physiology, 2011
AJP: Regulatory, Integrative and Comparative Physiology, 2011
Angiotensin-converting enzyme 2 (ACE2) is a component of the renin-angiotensin system, and its ex... more Angiotensin-converting enzyme 2 (ACE2) is a component of the renin-angiotensin system, and its expression and activity have been shown to be reduced in cardiovascular diseases. Enzymatic activity of ACE2 is commonly measured by hydrolysis of quenched fluorescent substrates in the absence or presence of an ACE2-specific inhibitor, such as the commercially available inhibitor DX600. Whereas recombinant human ACE2 is readily detected in mouse tissues using 1 μM DX600 at pH 7.5, the endogenous ACE2 activity in mouse tissues is barely detectable. We compared human, mouse, and rat ACE2 overexpressed in cell lines for their sensitivity to inhibition by DX600. ACE2 from all three species could be inhibited by DX600, but the half maximal inhibitory concentration (IC(50)) for human ACE2 was much lower (78-fold) than for rodent ACE2. Following optimization of pH, substrate concentration, and antagonist concentration, rat and mouse ACE2 expressed in a cell line could be accurately quantified with 10 μM DX600 (>95% inhibition) but not with 1 μM DX600 (<75% inhibition). Validation that the optimized method robustly quantifies ACE2 in mouse tissues (kidney, brain, heart, and plasma) was performed using wild-type and ACE2 knockout mice. This study provides a reliable method for measuring human, as well as endogenous ACE2 activity in rodents. Our data underscore the importance of validating the effect of DX600 on ACE2 from each particular species at the experimental conditions employed.
AJP: Heart and Circulatory Physiology, 2007