The expression and localization of serine proteinase inhibitor PI-6 mRNA in developmental and ischemic mouse brain

Targeted disruption of SPI3/Serpinb6 does not result in developmental or growth defects, leukocyte dysfunction, or susceptibility to stroke

Protease inhibitor 6 (PI-6/SERPINB6) is a widely expressed nucleocytoplasmic serpin. It inhibits granulocyte cathepsin G and neuronal neuropsin, and it is thought to protect cells from death caused by ectopic release or internalization of protease during stress such as infection or cerebral ischemia. To probe the biological functions of PI-6, we generated mice lacking its ortholog (SPI3/Serpinb6). SPI3-deficient mice developed normally and were fertile, and no abnormal pathology or increased sensitivity to cerebral ischemia was observed. There were no perturbations in leukocyte development or numbers, and recruitment of leukocytes to the peritoneal cavity was normal. SPI3-deficient mice were equally susceptible as wild-type mice to systemic Candida albicans infection, although there was a slight decrease in the ability of neutrophils from SPI3-deficient mice to kill C. albicans in vitro. Increased levels of a related inhibitor Serpinb1 (monocyte/neutrophil elastase inhibitor) in the tissues of targeted mice suggests that compensation by other serpins reduces the impact of SPI3 deficiency in these animals and may explain the lack of a more obvious phenotype.

Altered expression of randomly selected genes in mouse hippocampus after traumatic brain injury

Using a cDNA microarray method, we analyzed gene expression profiles in mouse hippocampus after traumatic brain injury (TBI). Of 6,400 randomly selected arrayed genes and expressed sequence tags from a mouse cDNA library, 253 were found to be differentially expressed (106 increased and 147 decreased). Genes involved in cell homeostasis and calcium signaling were primarily up-regulated while those encoding mitochondrial enzymes, metabolic molecules, and structural proteins were predominantly down-regulated. Equal numbers of genes related to inflammatory reactions showed increased or decreased expression. Importantly, a large proportion of the dysregulated genes we identified have not been reported as differentially expressed in TBI models. Semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR) analyses of representative genes confirmed the validity of the corresponding microarray findings. Thus, our microarray-based evaluation of gene expression in traumatically injured hippocampus identified both known and novel genes that respond to TBI. Further investigation of these candidate molecules may suggest new ways to attenuate the traumatic effects of brain injury.

Distribution of serine proteinase inhibitor, clade B, member 6 (Serpinb6) in the adult mouse brain

In the brain, Serpinb6 was identified as an endogenous inhibitor of neuropsin, a member of the S1 (clan SA) family of serine proteases [J. Biol. Chem. 276 (2001) 14562]. In the present study, we investigated the localization of Serpinb6 in the adult mouse brain using in situ hybridization histochemistry and immunohistochemistry. Region-specific patterns of expression were observed and two characteristics were recognized. First, the forebrain limbic area that expressed neuropsin mRNA contained Serpinb6 mRNA at moderate levels but not the lateral septum. On the other hand, Serpinb6 mRNA was also expressed moderately in the substantia nigra-ventral tegmental area system, whose fibers projected to the lateral septum. Additionally, Serpinb6 protein was detected in the lateral septum. Together, it was suggested that the expression of neuropsin in the brain is regulated entirely by Serpinb6. Second, Serpinb6 mRNA and the protein were strongly expressed in most somatic and visceral motoneurons among cranial nerve nuclei. This suggests that another serine protease is regulated by Serpinb6 in motoneurons and/or fibers.

Serine proteinase inhibitor 3 and murinoglobulin I are potent inhibitors of neuropsin in adult mouse brain

Extracellular serine protease neuropsin (NP) is expressed in the forebrain limbic area of adult brain and is implicated in synaptic plasticity. We screened for endogenous NP inhibitors with recombinant NP (r-NP) from extracts of the hippocampus and the cerebral cortex in adult mouse brain. Two SDS-stable complexes were detected, and after their purification, peptide sequences were determined by amino acid sequencing and mass spectrometry, revealing that target molecules were serine proteinase inhibitor-3 (SPI3) and murinoglobulin I (MUG I). The addition of the recombinant SPI3 to r-NP resulted in an SDS-stable complex, and the complex formation followed bimolecular kinetics with an association rate constant of 3.4 +/- 0.22 x 10(6) M(-1) s(-1), showing that SPI3 was a slow, tight binding inhibitor of NP. In situ hybridization histochemistry showed that SPI3 mRNA was expressed in pyramidal neurons in the hippocampal CA1-CA3 subfields, as was NP mRNA. Alternatively, the addition of purified plasma MUG I to r-NP resulted in an SDS-stable complex, and MUG I inhibited degradation of fibronectin by r-NP to 24% at a r-NP/MUG I molar ratio of 1:2. Immunofluorescence histochemistry showed that MUG I localized in the hippocampal neurons. These findings indicate that SPI3 and MUG I serve to inactivate NP and control the level of NP in adult brain, respectively.

Picornavirus receptor down-regulation by plasminogen activator inhibitor type 2

Therapeutic interference with virus-cell surface receptor interactions represents a viable antiviral strategy. Here we demonstrate that cytoplasmic expression of the serine protease inhibitor (serpin), plasminogen activator inhibitor type 2 (PAI-2), affords a high level of protection from lytic infection by multiple human picornaviruses. The antiviral action of PAI-2 was mediated primarily through transcriptional down-regulation of the following virus receptors: intercellular adhesion molecule 1 (ICAM-1, a cellular receptor for the major group of rhinoviruses), decay-accelerating factor (a cellular receptor for echoviruses and coxsackieviruses), and to a lesser extent the coxsackie-adenovirus receptor protein (a cellular receptor for group B coxsackieviruses and group C adenoviruses). Expression of related cell surface receptors, including membrane cofactor protein and the poliovirus receptor, remained unaffected. These findings suggest that PAI-2 and/or related serpins may form the basis of novel antiviral strategies against picornavirus infections and also therapeutic interventions against ICAM-1-mediated respiratory inflammation.