Targeting connexin 43 provides anti-inflammatory effects after intracerebral hemorrhage injury by regulating YAP signaling

Hailong Yu,Lilong Song,Yun Xu,Yuanyuan Zhao,Pinyi Liu,Jian Chen,Xiang Cao,Wei Li,Wenkui Yu,Beilei Chen

doi:10.1186/s12974-020-01978-z

Abstract

BackgroundIn the central nervous system (CNS), connexin 43 (Cx43) is mainly expressed in astrocytes and regulates astrocytic network homeostasis. Similar to Cx43 overexpression, abnormal excessive opening of Cx43 hemichannels (Cx43Hcs) on reactive astrocytes aggravates the inflammatory response and cell death in CNS pathologies. However, the role of excessive Cx43Hc opening in intracerebral hemorrhage (ICH) injury is not clear.MethodsHemin stimulation in primary cells and collagenase IV injection in C57BL/6J (B6) mice were used as ICH models in vitro and in vivo. After ICH injury, the Cx43 mimetic peptide Gap19 was used for treatment. Ethidium bromide (EtBr) uptake assays were used to measure the opening of Cx43Hcs. Western blotting and immunofluorescence were used to measure protein expression. qRT-PCR and ELISA were used to determine the levels of cytokines. Coimmunoprecipitation (Co-IP) and the Duolink in situ proximity ligation assay (PLA) were applied to measure the association between proteins.ResultsIn this study, Cx43 expression upregulation and excessive Cx43Hc opening was observed in mice after ICH injury. Delayed treatment with Gap19 significantly alleviated hematoma volume and neurological deficits after ICH injury. In addition, Gap19 decreased inflammatory cytokine levels in the tissue surrounding the hematoma and decreased reactive astrogliosis after ICH injury in vitro and in vivo. Intriguingly, Cx43 transcriptional activity and expression in astrocytes were significantly increased after hemin stimulation in culture. However, Gap19 treatment downregulated astrocytic Cx43 expression through the ubiquitin-proteasome pathway without affecting Cx43 transcription. Additionally, our data showed that Gap19 increased Yes-associated protein (YAP) nuclear translocation. This subsequently upregulated SOCS1 and SOCS3 expression and then inhibited the TLR4-NFκB and JAK2-STAT3 pathways in hemin-stimulated astrocytes. Finally, the YAP inhibitor, verteporfin (VP), reversed the anti-inflammatory effect of Gap19 in vitro and almost completely blocked its protective effects in vivo after ICH injury.ConclusionsThis study provides new insight into potential treatment strategies for ICH injury involving astroglial Cx43 and Cx43Hcs. Suppression of abnormal astroglial Cx43 expression and Cx43Hc opening by Gap19 has anti-inflammatory and neuroprotective effects after ICH injury.

Highlights

In the central nervous system (CNS), connexin 43 (Cx43) is mainly expressed in astrocytes and regulates astrocytic network homeostasis
This study provides new insight into potential treatment strategies for intracerebral hemorrhage (ICH) injury involving astroglial Cx43 and Cx43 hemichannels (Cx43Hcs)
We show that Gap19 provides neuroprotection and promotes cell survival by inhibiting inflammation-associated regulation of Yes-associated protein (YAP) signaling in reactive astrocytes after ICH injury

Summary

Introduction

In the central nervous system (CNS), connexin 43 (Cx43) is mainly expressed in astrocytes and regulates astrocytic network homeostasis. Similar to Cx43 overexpression, abnormal excessive opening of Cx43 hemichannels (Cx43Hcs) on reactive astrocytes aggravates the inflammatory response and cell death in CNS pathologies. Previous studies have shown that, like Cx43 overexpression, excessive opening of Cx43 hemichannels (Cx43Hcs) on the surface of reactive astrocytes results in the release of inflammatory factors that aggravate the inflammatory response of the local environment and recruit immune cells to the damaged area under pathological conditions [8, 9]. Our previous studies confirmed that astrocytic Cx43 overexpression and excessive Cx43Hc opening aggravate apoptosis and inflammation after cerebral ischemic injury [10, 11] These pathological processes are reversed by Cx43 mimetic peptides, including Gap, Gap, and Gap, which simulated the short nucleic acid sequences derived from the loop of Cx43. We employed Gap to block Cx43Hc opening in this study

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Conclusion