Identification of trypsin I as a candidate for influenza A virus and Sendai virus envelope glycoprotein processing protease in rat brain

Abstract

Extracellular cleavage of virus envelope fusion glycoprotein hemagglutinin (HA0) by host trypsin-like proteases is a prerequisite for the infectivity and pathogenicity of human influenza A viruses and Sendai virus. The common epidemic influenza A viruses are pneumotropic, but occasionally cause encephalopathy or encephalitis, although the HA0 processing enzyme in the brain has not been identified. In searching for the brain processing proteases, we identified a processing enzyme in rat brain that was inducible by infection with these viruses. The purified enzyme exhibited an apparent molecular mass of approximately 22 kDa on SDS-PAGE and the N-terminal amino acid sequence was consistent with that of rat pancreatic trypsin I. Its substrate specificities and inhibition profiles were the same as those of pancreatic trypsin I. In situ hybridization and immunohistochemical studies on trypsin I distribution revealed heavy deposits in the brain capillaries, particularly in the allocortex, as well as in clustered neuronal cells of the hippocampus. The purified enzyme efficiently processed the HA0 of human influenza A virus and the fusion glycoprotein precursor of Sendai virus. Our results suggest that trypsin I in the brain potentiates virus multiplication in the pathogenesis and progression of influenza-associated encephalopathy or encephalitis.

Diisopropylamine Dichloroacetate, a Novel Pyruvate Dehydrogenase Kinase 4 Inhibitor, as a Potential Therapeutic Agent for Metabolic Disorders and Multiorgan Failure in Severe Influenza

“…This sparing effect is probably related to the protective role of the blood-brain barrier against the transport of pathogenic molecules into the brain. However, trypsin in the brain is distributed mainly in cerebrovascular endothelial cells and hippocampal neuronal cells [12], [38], and it is up-regulated in vascular endothelial cells by proinflammatory cytokines in the blood [7]. These findings suggest that the high levels of proinflammatory cytokines in the blood after IAV infection induce trypsin in cerebrovascular endothelial cells and DADA may suppress trypsin levels in the brain through down-regulation of cytokines.…”

“…Since the levels of proinflammatory cytokines are closely interconnected to those of trypsin and influenza virus replication rate in target organs through the influenza virus–cytokine–trypsin cycle [7], [12], [13], we analyzed the effects of DADA on viral replication and trypsin expression in the lungs during the peak duration at days 2, 4 and 6 post-infection [7], [36], [37] and in other organs at day 4 post-infection [7], [13], [38]. Quantitative real-time PCR showed a significant reduction in the copy number of the viral non-structure protein 1 (NS-1) RNA gene segment in the lungs of infected mice treated with DADA at days 4 and 6 post-infection, compared with the vehicle-treated mice (Figure 6).…”

The complex link between influenza and severe sepsis

“…Several animal studies showed that host cellular trypsin-like proteases that activate viral fusion activity of hemagglutinin partially determine viral pathogenicity and infectivity 8 , 43 , 44 44 which can efficiently convert pro-MMP-9 to active MMP-9; 45 these both proteases can synergistically degrade the basement membrane proteins, including tight intercellular junctions and the blood–brain barrier 46 …”

Host envelope glycoprotein processing proteases are indispensable for entry into human cells by seasonal and highly pathogenic avian influenza viruses

“…In addition, a rare but often fatal encephalopathy caused by infection with a pneumotropic IAV has been reported in children with Reye's syndrome and influenza-associated encephalopathy (Delorme and Middleton 1979; Fujimoto et al, 1998). Recently, we reported that IAV infection can markedly upregulate latent pancreatic trypsin in the brain (Le et al, 2006) and various organs that may have not only a HA 0 processing activity but also a maturase activity of upregulated proMMP-9 (Yamada et al, 2006). …”