[show abstract][hide abstract] ABSTRACT: Reactive oxygen species (ROS) are thought to contribute to the pathogenesis of necrotizing enterocolitis (NEC). Mitochondria as a major source of intracellular ROS and apoptotic signaling during oxidative stress in NEC have not been investigated. We sought to determine: (1) the effects of oxidative stress on intestinal mitochondrial apoptotic signaling, and (2) the role of growth factors in this process.
We used Swiss-Webster mice pups, and rat intestinal epithelial (RIE)-1, mitochondrial DNA-depleted RIE-1 cell line (RIE-1-ρ°) and human fetal intestinal epithelial cells (FHs74 Int) for our studies.
H(2)O(2) induced apoptosis and ROS production. ROS-mediated activation of apoptotic signaling was significantly attenuated with mitochondrial silencing in RIE-1-ρ° cells. Growth factors, especially IGF-1, attenuated this response to H(2)O(2) in intestinal epithelial cells.
Our findings suggest that mitochondria are a major source of intestinal apoptotic signaling during oxidative stress, and modulating mitochondrial apoptotic responses may help ameliorate the effects of NEC.
Pediatric Surgery International 03/2011; 27(8):871-7. · 1.22 Impact Factor
[show abstract][hide abstract] ABSTRACT: Oxidative stress and inflammation may contribute to the disruption of the protective gut barrier through various mechanisms; mitochondrial dysfunction resulting from inflammatory and oxidative injury may potentially be a significant source of apoptosis during necrotizing enterocolitis (NEC). Tumor necrosis factor (TNF)-alpha is thought to generate reactive oxygen species (ROS) and activate the apoptosis signal-regulating kinase 1 (ASK1)-c-Jun N-terminal kinase (JNK)/p38 pathway. Hence, the focus of our study was to examine the effects of TNF-alpha/ROS on mitochondrial function, ASK1-JNK/p38 cascade activation in intestinal epithelial cells during NEC.
We found (a) abundant tissue TNF-alpha and ASK1 expression throughout all layers of the intestine in neonates with NEC, suggesting that TNF-alpha/ASK1 may be a potential source (indicators) of intestinal injury in neonates with NEC; (b) TNF-alpha-induced rapid and transient activation of JNK/p38 apoptotic signaling in all cell lines suggests that this may be an important molecular characteristic of NEC; (c) TNF-alpha-induced rapid and transient ROS production in RIE-1 cells indicates that mitochondria are the predominant source of ROS, demonstrated by significantly attenuated response in mitochondrial DNA-depleted (RIE-1-rho) intestinal epithelial cells; (d) further studies with mitochondria-targeted antioxidant PBN supported our hypothesis that effective mitochondrial ROS trapping is protective against TNF-alpha/ROS-induced intestinal epithelial cell injury; (e) TNF-alpha induces significant mitochondrial dysfunction in intestinal epithelial cells, resulting in increased production of mtROS, drop in mitochondrial membrane potential (MMP) and decreased oxygen consumption; (f) although the significance of mitochondrial autophagy in NEC has not been unequivocally shown, our studies provide a strong preliminary indication that TNF-alpha/ROS-induced mitochondrial autophagy may play a role in NEC, and this process is a late phenomenon.
Paraffin-embedded intestinal sections from neonates with NEC and non-inflammatory condition of the gastrointestinal tract undergoing bowel resections were analyzed for TNF-alpha and ASK1 expression. Rat (RIE-1) and mitochondrial DNA-depleted (RIE-1-rho) intestinal epithelial cells were used to determine the effects of TNF-alpha on mitochondrial function.
Our findings suggest that TNF-alpha induces significant mitochondrial dysfunction and activation of mitochondrial apoptotic responses, leading to intestinal epithelial cell apoptosis during NEC. Therapies directed against mitochondria/ROS may provide important therapeutic options, as well as ameliorate intestinal epithelial cell apoptosis during NEC.
Oxidative Medicine and Cellular Longevity 01/2009; 2(5):297-306.
[show abstract][hide abstract] ABSTRACT: Previously, we demonstrated that protein kinase D (PKD) plays a protective role during H(2)O(2)-induced intestinal cell death. Here, we sought to determine whether this effect is mediated by nuclear factor-kappaB (NF-kappaB) and mitogen-activated protein kinases (MAPKs). Treatment with H(2)O(2) activated NF-kappaB in RIE-1 cells; H(2)O(2) also induced the translocation of NF-kappaB p65 as well as phosphorylation of IkappaB-alpha. PKD1 siRNA inhibited H(2)O(2)-induced activation, translocation of NF-kappaB, and phosphorylation of IkappaB-alpha. We also found that overexpression of wild type PKD1 attenuated H(2)O(2)-induced phosphorylation of p38 MAPK and its upstream activator, MAPK kinase (MKK) 3/6, whereas the phosphorylation was increased by PKD1 siRNA or kinase-dead PKD1. Phosphorylation of neither extracellular signal-regulated kinases (ERK) 1/2 nor c-Jun N-terminal kinases (JNK) was altered by PKD1 plasmids or siRNA. Our findings suggest that PKD protects intestinal cells through up-regulation of NF-kappaB and down-regulation of p38 MAPK.
Biochemical and Biophysical Research Communications 01/2009; 378(3):610-4. · 2.41 Impact Factor
[show abstract][hide abstract] ABSTRACT: We recently demonstrated that protein kinase D (PKD) exerts a protective function during oxidative stress-induced intestinal epithelial cell injury; however, the exact role of DAG kinase (DGK)zeta, an isoform expressed in intestine, during this process is unknown. We sought to determine the role of DGK during oxidative stress-induced intestinal cell injury and whether DGK acts as an upstream regulator of PKD. Inhibition of DGK with R59022 compound or DGKzeta siRNA transfection decreased H2O2-induced RIE-1 cell apoptosis as measured by DNA fragmentation and increased PKD phosphorylation. Overexpression of kinase-dead DGKzeta also significantly increased PKD phosphorylation. Additionally, endogenous nuclear DGKzeta rapidly translocated to the cytoplasm following H2O2 treatment. Our findings demonstrate that DGK is involved in the regulation of oxidative stress-induced intestinal cell injury. PKD activation is induced by DGKzeta, suggesting DGK is an upstream regulator of oxidative stress-induced activation of the PKD signaling pathway in intestinal epithelial cells.
Biochemical and Biophysical Research Communications 11/2008; 375(2):200-4. · 2.41 Impact Factor
[show abstract][hide abstract] ABSTRACT: Protein kinase D (PKD) is a novel protein serine kinase that has recently been implicated in diverse cellular functions, including apoptosis and cell proliferation. The purpose of our present study was 1) to define the activation of PKD in intestinal epithelial cells treated with H2O2, an agent that induces oxidative stress, and 2) to delineate the upstream signaling mechanisms mediating the activation of PKD. We found that the activation of PKD is induced by H2O2 in both a dose- and time-dependent fashion. PKD phosphorylation was attenuated by rottlerin, a selective PKC-delta inhibitor, and by small interfering RNA (siRNA) directed against PKC-delta, suggesting the regulation of PKD activity by upstream PKC-delta. Activation of PKD was also blocked by a Rho kinase (ROK)-specific inhibitor, Y-27632, as well as by C3, a Rho protein inhibitor, demonstrating that the Rho/ROK pathway also mediates PKD activity in intestinal cells. In addition, H2O2-induced PKC-delta phosphorylation was inhibited by C3 treatment, further suggesting that PKC-delta is downstream of Rho/ROK. Interestingly, H2O2-induced intestinal cell apoptosis was enhanced by PKD siRNA. Together, these results clearly demonstrate that oxidative stress induces PKD activation in intestinal epithelial cells and that this activation is regulated by upstream PKC-delta and Rho/ROK pathways. Importantly, our findings suggest that PKD activation protects intestinal epithelial cells from oxidative stress-induced apoptosis. These findings have potential clinical implications for intestinal injury associated with oxidative stress (e.g., necrotizing enterocolitis in infants).