Heme oxygenase-1 is an equid alphaherpesvirus 8 replication restriction host protein and suppresses viral replication via the PKCβ/ERK1/ERK2 and NO/cGMP/PKG pathway

Equid alphaherpesvirus 8 (EqHV-8) is one of the most economically important viruses that is known to cause severe respiratory disease, abortion, and neurological syndromes in equines. However, no effective vaccines or therapeutic agents are available to control EqHV-8 infection. Heme oxygenase-1 (HO-1) is an antioxidant defense enzyme that displays significant cytoprotective effects against different viral infections. However, the literature on the function of HO-1 during EqHV-8 infection is little. We explored the effects of HO-1 on EqHV-8 infection and revealed its potential mechanisms. Our results demonstrated that HO-1 induced by cobalt-protoporphyrin (CoPP) or HO-1 overexpression inhibited EqHV-8 replication in susceptible cells. In contrast, HO-1 inhibitor (zinc protoporphyria) or siRNA targeting HO-1 reversed the anti-EqHV-8 activity. Furthermore, biliverdin, a metabolic product of HO-1, mediated the anti-EqHV-8 effect of HO-1 via both the protein kinase C (PKC)β/extracellular signal-regulated kinase (ERK)1/ERK2 and nitric oxide (NO)-dependent cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) signaling pathways. In addition, CoPP protected the mice by reducing the EqHV-8 infection in the lungs. Altogether, these results indicated that HO-1 can be developed as a promising therapeutic strategy to control EqHV-8 infection.IMPORTANCEEqHV-8 infections have threatened continuously donkey and horse industry worldwide, which induces huge economic losses every year. However, no effective vaccination strategies or drug against EqHV-8 infection until now. Our present study found that one host protien HO-1 restrict EqHV-8 replication in vitro and in vivo. Furthermore, we demonstrate that HO-1 and its metabolite biliverdin suppress EqHV-8 relication via the PKCβ/ERK1/ERK2 and NO/cGMP/PKG pathways. Hence, we believe that HO-1 can be developed as a promising therapeutic strategy to control EqHV-8 infection.

Pathogenicity and host cytokines response of EqHV-8 infection in C57BL/6J mice

Equid herpesvirus type 8 (EqHV-8) is known to cause abortion, respiratory signs, and viral encephalitis in equines. EqHV-8 has been reported to cause serious economic losses in large-scale donkey farms in China. However, little is known about the viral replication and immune reaction in the brains and lungs of EqHV-8-induced C57BL/6J mice. We determined the pathogenicity and immune status in a mice model. The C57BL/6J mice were infected with the EqHV-8 donkey/Shandong/10/2021 strain, and the clinical signs and body weights were evaluated every day. In addition, viremia, virus loads, and the expression of pro-inflammatory cytokines in mice brains and lungs were assessed at 1, 3, 5, and 7 days post infection (dpi). Our results demonstrated that mice in the EqHV-8 infected group displayed body weight loss, dyspnea signs, and viremia. The expression of interleukin (IL)-1β, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, IL-6 mRNA was increased in the brains and lungs of EqHV-8-infected mice than that in control group at 5 dpi and 7 dpi, and IL-12a expression was increased at 7 dpi. These data indicated that EqHV-8 elicited a strong cytokines response, caused neurogenic disease and respiratory signs in C57BL/6J mice, thus revealing the pathogenicity of EqHV-8.

Cobalt Protoporphyrin Blocks EqHV-8 Infection via IFN-α/β Production

Equid alphaherpesvirus type 8 (EqHV-8) is the causative agent of severe respiratory disease, abortions, and neurological syndromes in equines and has resulted in huge economic losses to the donkey industry. Currently, there exist no therapeutic molecules for controlling EqHV-8 infection. We evaluated the potential antiviral activity of cobalt protoporphyrin (CoPP) against EqHV-8 infection. Our results demonstrated that CoPP inhibited EqHV-8 infection in susceptible cells and mouse models. Furthermore, CoPP blocked the replication of EqHV-8 via HO-1 (heme oxygenase-1) mediated type I interferon (IFN) response. In conclusion, our data suggested that CoPP could serve as a novel potential molecule to develop an effective therapeutic strategy for EqHV-8 prevention and control.