Myosin translocation in retinal pericytes during free-radical induced apoptosis

Abstract

Vascular pathologies induced by ischemia/reperfusion involve the production of reactive oxygen species (ROS) that in part cause tissue injury. The production of ROS that occurs upon reperfusion activates specific second messenger pathways. In diabetic retinopathy there is a characteristic loss of the microvascular pericyte. Pericytes are more sensitive than endothelial cells to low concentrations of ROS, such as hydrogen peroxide (H(2)O(2)) when tested in vitro. Whether the pericyte loss is due to toxic cell death triggered by the noxious H(2)O(2) or apoptosis, due to activation of specific second messenger pathways, is unknown. During apoptosis, a cell's nucleus and cytoplasm condense, the cell becomes fragmented, and ultimately forms apoptotic bodies. It is generally assumed that apoptosis depends on nuclear signaling, but cytoplasmic morphological processes are not well described. We find that exposing cultured retinal pericytes to 100 microM H(2)O(2) for 30 min leads to myosin heavy chain translocation from the cytosol to the cytoskeleton and a significant decrease in cell surface area. Pericyte death follows within 60-120 min. Exposing cells to 150 mJ/cm(2) ultraviolet radiation, an alternate free radical generating system, also causes pericyte myosin translocation and apoptosis. Proteolytic cleavage of actin is not observed in pericyte apoptosis. 3-aminobenzamide, a pharmacological inhibitor of the cleavage and activation of the DNA-repairing enzyme poly (ADP-ribose) polymerase (PARP) inhibits pericyte apoptosis, and prevents myosin translocation. Deferoxamine, an iron chelator known to interfere with free radical generation, also inhibits pericyte myosin translocation, contractility, and cell death. Myosin translocation to the cytoskeleton may be an early step in assembly of a competent contractile apparatus, which is involved in apoptotic cell condensation. These results suggest that pericyte loss associated with increased free radical production in diabetic retina may be by an apoptotic phenomenon.

Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke

“…Apoptosis of pericytes was evident in ischemic areas after reperfusion, when production of ROS was elevated. Anti-oxidative treatment inhibited pericyte death after I/R, 243 suggesting a key role for ROS in the demise of pericytes. 29 Overall, pericytes are much more than supportive cells to endothelium.…”

“…29, 241 In support of a ROS-dependent mechanism, hydrogen peroxide and radiation-induced production of ROS cause contraction of cultured pericytes. 243 The precise mechanism(s) underlying oxidative stress-induced pericyte contraction is unclear. Possible mechanisms involve excessive calcium influx during reperfusion and inactivation of potassium channels or sodium/hydrogen exchangers.…”

Pericytes in Brain Injury and Repair After Ischemic Stroke

“…Exposure of cultured retinal pericytes to hydrogen peroxide (H2O2) or ultraviolet radiation, a free radical generating system, led to translocation of myosin heavy chain from cytosol to the cytoskeleton and the following contraction of pericytes. This could be rescued by the elimination of free radicals or oxidative stress [59]. Yemisci M et, al.…”

Early Loss of Pericytes and Perivascular Stromal Cell-Induced Scar Formation after Stroke

“…In other experimental models, PCs have been shown to be very sensitive to hypoxia 34 and to reactive oxygen species. 35 Adenosine triphosphate, which is released by necrotic cells and secreted by astrocytes in the injured brain tissue, may cause PC death via activation of P2X7 purinergic receptors. 36 In our model, TUNEL-positive PCs, indicative of cell death, were frequent starting at day 1 after ischemia; expression of CC3 in the ischemic tissue was also detected with a peak 3 days after the insult.…”