Transient ischemia induces massive nuclear accumulation of SUMO2/3-conjugated proteins in spinal cord neurons

Abstract

Objectives: The objective of this study is to determine whether transient spinal cord ischemia activates small ubiquitin-like modifier (SUMO1-3) conjugation, a post-translational protein modification that protects neurons from ischemia-like conditions. Methods: Mice were subjected to 8-12 min of spinal cord ischemia and 3-24 h of recovery using a newly developed experimental model. To characterize the model, activation of stress response pathways induced after spinal cord ischemia, previously observed in other experimental models, was verified by western blot analysis. Levels and subcellular localization of SUMO-conjugated proteins in spinal cords were evaluated by western blot analysis and immunohistochemistry, respectively. Results: Following transient spinal cord ischemia, stress responses were activated as indicated by increased phosphorylation of eukaryotic initiation factor 2 (eIF2a), extracellular signal-regulated kinases (ERK1/2) and Akt. SUMO1 conjugation was not altered, but a selective rise in levels of SUMO2/3-conjugated proteins occurred, peaking at 6 h reperfusion. The marked activation of SUMO2/ 3 conjugation was a neuronal response to ischemia, as indicated by co-localization with the neuronal marker NeuN, and was associated with nuclear accumulation of SUMO2/3-conjugated proteins. Conclusion: Our study suggests that spinal cord neurons respond to ischemic stress by activation of SUMO2/3 conjugation. Many of the identified SUMO target proteins are transcription factors and other nuclear proteins involved in gene expression and genome stability. It is therefore concluded that the post-ischemic activation of SUMO2/3 conjugation may define the fate of neurons exposed to a transient interruption of blood supply, and that this pathway could be a therapeutic target to increase the resistance of spinal cord neurons to transient ischemia.

Aging Is Associated With Impaired Activation of Protein Homeostasis‐Related Pathways After Cardiac Arrest in Mice

“…These findings suggest that aging is associated with a decline in the capacity of cells to activate these posttranslational modifications, particularly SUMOylation and O‐GlcNAcylation. Rapid activation of both modifications has been reported in various postischemic organs 6, 8, 27, 28, 29, 30. Notably, in the present study, these were the only posttranslational modifications that showed impaired activation in both brain and kidney of aged mice.…”

Ubiquitin-dependent and independent roles of SUMO in proteostasis

“…Interestingly, it was observed that SUMO2/3 conjugation is massively increased in brains of hibernating thirteen-lined ground squirrels ( Ictidomys tridecemlineatus ) during torpor (76). Consistently, multiple studies showed a high increase of SUMO conjugation after transient ischemia in vitro and in vivo (18, 76, 79, 131, 142, 143). This raises the intriguing question about the functional contribution of SUMOylation to protect cells from damage during ischemia.…”

SUMO3 Modification Accelerates the Aggregation of ALS-Linked SOD1 Mutants

“…It is thus speculated that sumoylation may trigger such prion-like characteristics in mutant SOD1. Multiple lines of evidence indicate that SOD1 aggregate formation closely correlates with cytotoxicity in cellular models and decreased survival in model mice [1], [18]–[21], [23]. Taken together, it is assumed that the sumoylation-induced acceleration of SOD1 aggregation is linked to neurotoxicity in ALS pathogenesis.…”

“…These findings provide evidence for the involvement of sumoylation in ALS pathogenesis. Since SUMOs are expressed in spinal cord neurons [20], [21], it is assumed that sumoylation may have a pathological role in motor neurons as well as astrocytes. Fei et al reported that the human SOD1 protein is sumoylated and stabilized by SUMO1, suggesting that sumoylation is linked to SOD1 aggregation [22].…”