Neuron-specific SUMO knockdown suppresses global gene expression response and worsens functional outcome after transient forebrain ischemia in mice

Abstract

Small ubiquitin-like modifier (SUMO) conjugation (SUMOylation) plays key roles in neurologic function in health and disease. Neuronal SUMOylation is essential for emotionality and cognition, and this pathway is dramatically activated in post-ischemic neurons, a neuroprotective response to ischemia. It is also known from cell culture studies that SUMOylation modulates gene expression. However, it remains unknown how SUMOylation regulates neuronal gene expression in vivo, in the physiologic state and after ischemia, and modulates post-ischemic recovery of neurologic function. To address these important questions, we used a SUMO1-3 knockdown (SUMO-KD) mouse in which a Thy-1 promoter drives expression of 3 distinct microRNAs against SUMO1-3 to silence SUMO expression specifically in neurons. Wild-type and SUMO-KD mice were subjected to transient forebrain ischemia. Microarray analysis was performed in hippocampal CA1 samples, and neurologic function was evaluated. SUMOylation had opposite effects on neuronal gene expression before and after ischemia. In the physiological state, most genes regulated by SUMOylation were up-regulated in SUMO-KD compared to wild-type mice. Brain ischemia/reperfusion significantly modulated the expression levels of more than 400 genes in wild-type mice, with a majority of those genes upregulated. The extent of this post-ischemic transcriptome change was suppressed in SUMO-KD mice. Moreover, SUMO-KD mice exhibited significantly worse functional outcome. This suggests that suppression of global gene expression response in post-ischemic brain due to SUMO knockdown has a negative effect on post-ischemic neurologic function. Together, our data provide a basis for future studies to mechanistically link SUMOylation to neurologic function in health and disease.

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

“…A large body of evidence suggests that SUMOylation is an endogenous prosurvival pathway, and that increasing global SUMOylation protects the brain against ischemic insult 31, 32, 33. For example, transgenic mice that exhibit elevated basal levels of global SUMOylation are more resistant to ischemia‐induced brain damage,32 whereas transgenic mice in which SUMO expression is significantly silenced show worse functional outcome after global cerebral ischemia 31.…”

“…For example, transgenic mice that exhibit elevated basal levels of global SUMOylation are more resistant to ischemia‐induced brain damage,32 whereas transgenic mice in which SUMO expression is significantly silenced show worse functional outcome after global cerebral ischemia 31. Currently, only a limited number of small molecules that may be capable of increasing SUMOylation in vivo are available for testing in disease models related to I/R injury 33.…”

SUMOylation in brain ischemia: Patterns, targets, and translational implications

“…13,20 SUMOylation in experimental brain ischemia/stroke A substantial body of evidence has shown that both global and focal transient cerebral ischemia dramatically increase the levels of SUMO-conjugated proteins (especially SUMO2/3 conjugation) in rodent brains shortly after reperfusion, and that this process may be neuroprotective (summarized in Table 1). [3][4][5][21][22][23] However, it is prudent to note that evidence of SUMO activation in post-ischemic human brain tissue has yet to be put forward and should therefore be actively pursued.…”

Quantitative high‐throughput screening identifies cytoprotective molecules that enhance SUMO conjugation via the inhibition of SUMO‐specific protease (SENP)2

“…Based on a substantial body of evidence, it is now believed that SUMOylation is an endogenous neuroprotective mechanism (12,(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). For example, in vitro studies have shown that silencing SUMOs sensitizes primary neurons to oxygen-glucose deprivation (OGD)induced damage, whereas overexpression of SUMO in cortical neurons induced OGD tolerance (12).…”

“…For example, in vitro studies have shown that silencing SUMOs sensitizes primary neurons to oxygen-glucose deprivation (OGD)induced damage, whereas overexpression of SUMO in cortical neurons induced OGD tolerance (12). Furthermore, compared to wild-type mice, mice overexpressing Ubc9 demonstrated improved resistance to focal ischemia-induced damage (23), and transgenic mice in which SUMO-1-3 were knocked down in neurons displayed worse functional outcomes after transient forebrain ischemia (24). SUMOylation is increased during animal hibernation and clinically relevant hypothermia (12,18,25,26), and it has been proposed that increased global SUMOylation is a key mechanism underlying hypothermia-induced protection (12,18,21,27).…”