Date Published: March 7, 2019
Publisher: Public Library of Science
Author(s): Tonglin Lu, Yongyi Zou, Xu Zhou, Wenna Peng, Zhiping Hu, Guo-Chang Fan.
Recent research has demonstrated that small heat shock protein (sHsp) phosphorylation plays a variety of roles in neural cells. While the phosphorylation of serine 16 (Ser16) is blocked, Hsp20 no longer has neuroprotective effects. To further investigate the mechanism underlying this process, oxygen-glucose deprivation and reperfusion (OGD/R) was used with human SH-SY5Y cells and mouse N2a neuroblastoma cells. When SH-SY5Y and N2a cells were transfected with pEGFP-Hsp20(WT), pEGFP-Hsp20(S16A), and pEGFP-Hsp20(S16D) plasmids, the Golgi apparatus (GA) became more swollen and scattered, and many small fragments formed in the MOCK and S16A groups after OGD/R (P < 0.05). Meanwhile, the endoplasmic reticulum (ER) network was reduced, and the lamellar structure increased. However, these changes were not as obvious in the WT and S16D groups. Additionally, after OGD/R, Golgi Stress related protein contents were increased in the WT and S16D groups compared with the MOCK and S16A groups (P < 0.05). However, ER Stress related protein contents were decreased in the WT and S16D groups compared with the MOCK and S16A groups (P < 0.05). Our study demonstrates that Hsp20 phosphorylation on Ser16 protects against not only OGD/R-induced GA fragmentation in SH-SY5Y cells and N2a cells via Golgi stress but also OGD/R-induced ER structural changes in SH-SY5Y cells via ER stress. These findings suggest that Hsp20 is a potential drug target for ischemia stroke treatment.
Ischemic stroke is the most common type of stroke. Recent studies have shown that in China, the mortality rate of ischemic stroke patients is approximately 3.3–5.2% during the first month after disease onset and is 11.4–15.4% during the first year after disease onset. Early diagnosis, treatment, rehabilitation and prevention of ischemic stroke should be emphasized . Currently, the ultra-early use of recombinant tissue plasminogen activator for intravenous thrombolysis is the most effective drug treatment to improve the outcome of acute ischemic stroke. However, thrombolytic therapy has certain time limitation and may induce many complications. Therefore, a better approach is needed to treat ischemic stroke. Reducing ischemic reperfusion injury is considered an effective measure for treating it.
Hsp20 is a stress-related protein that is widely expressed in the cerebral cortex. After hypoxia, the protein content of Hsp20 in hippocampal tissues increased rapidly, which was one of the initial landmark events of hypoxia. Previous studies have confirmed that Hsp20 has protective effects on nerve cells during oxy-glucose deprivation/reperfusion, but it is not clear whether the neuro-protective effects of Hsp20 are related to GA. Golgi stress represents GA’s ability to respond to homeostasis in cells. However, if the homeostasis in cells exceeds its ability to respond, Golgi fragmentation, related gene and protein changes will occur [3, 4]. In this study, we found that the Golgi structure in the empty vector groups and the S16A groups were damaged after OGD/R. Its morphology becomes more swollen, its spatial range is enlarged, and many small fragments form. However, the morphological changes of GA in S16D groups and WT groups were relatively less obvious, and the fragmentation of GA was reduced. These results suggest that phosphorylation of Hsp20 serine 16 site in mouse N2a cells and human sh-sy5y cells has a protective effect on Golgi fragmentation caused by OGD/R. Golgi stress is activated.