Abstract
Tissue plasminogen activator (tPA) is an immediate-early gene important for regulating physiological processes like synaptic plasticity and neurovascular coupling. It has also been implicated in several pathological processes including blood-brain barrier permeability, seizure progression, and stroke. These varied reports suggest that tPA is a pleiotropic mediator whose actions are highly compartmentalized in space and time. The specific localization of tPA, therefore, can provide useful information about its function. Accordingly, the goal of this study was to provide a detailed characterization of tPA’s regional, cellular, and subcellular localization in the brain. To achieve this, two new transgenic mouse lines were utilized: (1) a PlatβGAL reporter mouse, which houses the β-galactosidase gene in the tPA locus and (2) a tPABAC-Cerulean mouse, which has a cerulean-fluorescent protein fused in-frame to the tPA C-terminus. Using these two transgenic reporters, we show that while tPA is expressed throughout most regions of the adult murine brain, it appears to be preferentially targeted to fiber tracts in the limbic system. In the hippocampus, confocal microscopy revealed tPA-Cerulean (tPA-Cer) puncta localized to giant mossy fiber boutons and astrocytes in stratum lucidum. With amplification of the tPA-Cer signal, somatically localized tPA was also observed in the stratum oriens/alveus layer of both CA1 and CA3 subfields. Co-immunostaining of tPA-Cer and interneuronal markers indicates that these tPA-positive cell bodies belong to a subclass of somatostatin/oriens-lacunosum moleculare interneurons. Together, these data imply that tPA’s localization is differentially regulated, suggesting that its neuromodulatory effects may be compartmentalized and specialized to cell-type.
Significance Statement The serine protease tissue plasminogen activator (tPA) has been shown to modulate numerous neurologic processes including synaptic plasticity and neurodegeneration. Many of the functional conclusions drawn about tPA activity, however, have not been affirmed by high-resolution, imaging analysis of tPA localization. To address these shortcomings, we used two new transgenic reporter mice to provide a detailed characterization of tPA expression in the adult murine brain. A comparison of these reporter mice demonstrates a differential expression pattern between the sites of tPA synthesis and its targeted localization in the hippocampus, amygdala, and basal ganglia. Moreover, colocalization and co-expression analysis reveals that tPA is primarily trafficked to pre-synaptic structures and that it’s predominant somatic and/or axonal localization is cell-type specific.
Footnotes
The authors declare no competing financial interests.
This work was supported by National Institutes of Health Grants HL055374, and NS079639 (to D.A. L.), and T32-HL125242 and T32 - GM008322 (T.K.S.).
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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