Abstract Body: Background: Thymosin alpha 1 (Tα1) had been used in kinds of inflammatory and immunodeficiency diseases as an immunomodulator. According to our clinic observation, patients with acute ischemic stroke (AIS) treated with Tα1 to prevent/cure post-stroke infection display favorable stroke outcome. Whether Tα1 exerts direct neuronal protection besides immunomodulation remains elusive.

Aim: To explore the effect of Tα1 on neuronal protection after AIS and unveil the underlying mechanisms.

Method: In vivo: 8-10 weeks old male Wild type (WT) mice were subjected to 60 minutes middle cerebral artery occlusion (tMCAO) and administrated Tα-1 by intraperitoneal injection. Ex vivo: Primary mouse neuron is subjected to 60 min oxygen and glucose deprivation (OGD), followed by Tα-1 treatment.

Results: Compared with untreated group, Tα1 treatment displayed decreased infarct volume, limited neuronal loss, attenuated white matter injury，restricted neuroinflammation and improved neurological functions. Treatment of antibiotics or glucocorticoid failed to substitute the therapeutic effects of Tα1, indicating extra protection of Tα1 treatment besides anti-infection and immunomodulation. As for primary mouse neuron, Tα1 treatment showed fewer neuron death and higher cell viability upon OGD stimulation. Both in vivo and ex vivo experiments revealed that Tα1 directly inhibited ischemia-induced neuronal death. Mechanistically, Tα1 enhanced mitophagy by down-regulating Drp1, thus promoted mitochondrial renewal and supported neuronal viability.

Conclusions: Our results identified that Tα1 possessed direct neuronal protection and improved prognosis of AIS. Given the multi-functions of Tα1 including anti-infection, immunomodulation and neuronal protection, we propose that Tα1 is a promising therapy against AIS.