Modulation of neuronal plasticity by extracellular serine proteases and their inhibitors : proteolytic control of NMDA receptors

Serine proteases are enzymes catalyzing protein cleavage. Because of their capability to cleave a wide variety of substrates, they are involved in many critical physiological processes such as digestion, hemostasis, reproduction and immune response, as well as in developmental processes, signal transduction and apoptosis. In the last years, there is also increasing evidence for their role in the control of plasticity-related events in the adult and developing central nervous system, and involvement in phenomena such as memory and learning. Protease nexin-1 (PN-1) is a 43 kDa glycoprotein belonging to the serpin superfamily. It strongly inhibits the activity of several serine proteases such as thrombin, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), trypsin and plasmin. PN-1 has a complex spatial and temporal expression pattern in the adult and developing nervous system, and its expression is enhanced upon CNS lesions. Mice lacking PN-1 have reduced long-term potentiation (LTP) in the hippocampus, and are more prone to seizures, while mice overexpressing it develop a progressive neurodegenerative disorder. These findings suggest a role for PN-1 in brain function and homeostasis. In this thesis the role of PN-1 in adult brain plasticity was examined. Activitydependent expression of PN-1 was demonstrated using an in vivo reporter system. PN-1 was found to be crucial for the control of brain proteolytic activity, and PN-1-/mice displayed decreased levels of the NR1 subunit of the N-methyl-D-aspartate (NMDA) receptor in the cortex and hippocampus. Electrophysiological examination of adult PN-1-/- mice revealed decreased NMDA receptor signaling in the barrel cortex, and decreased sensory evoked potentials upon whisker stimulation. Behavioral tests showed that PN-1-/- mice also displayed impaired whisker-dependent sensory motor function. Thus, a tight control of serine protease activity was shown to be critical for the in vivo function of NMDA receptors, and the proper function of sensory pathways

Mice with a naturally occurring DISC1 mutation display a broad spectrum of behaviors associated to psychiatric disorders

Disrupted in schizophrenia-1 (DISC1) gene is associated with several neuropsychiatric disorders as it is disrupted by a balanced translocation involving chromosomes 1 and 11 in a large Scottish pedigree with high prevalence of schizophrenia, bipolar disorder and major depression. Since its identification, several mouse models with DISC1 genetic modifications have been generated using different approaches. Interestingly, a natural deletion of 25bp in the 129 mouse strain alters the DISC1 gene reading frame leading to a premature stop codon very close to the gene breakpoint in the mutant allele of the Scottish family. In the present study we confirmed that the 129DISC1Del mutation results in reduced level of full length DISC1 in hippocampus of heterozygous mice and we have characterized the behavioral consequences of heterozygous 129DISC1Del mutation in a mixed B6129 genetic background. We found alterations in spontaneous locomotor activity (hyperactivity in males and hypoactivity in females), deficits in pre-pulse inhibition (PPI) and also increased despair behavior in heterozygous 129DISC1Del mice, thus reproducing typical behaviors associated to psychiatric disorders. Since this mouse strain is widely and commercially available, we propose it as an amenable tool to study DISC1-related biochemical alterations and psychiatric behaviors. © 2014 Gómez-Sintes, Kvajo, Gogos and Lucas.Thiswork was supported by Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas(CiberNed-Instituto de Salud CarlosIII)and by grants from Ministerio de Ciencia(MEC,MICINN)SAF2009-08233 and SAF2012-34177 and Fundación Ramón ArecesPeer Reviewe

Mice lacking protease nexin-1 show delayed structural and functional recovery after sciatic nerve crush

Multiple molecular mechanisms influence nerve regeneration. Because serine proteases were shown to affect peripheral nerve regeneration, we performed nerve crush experiments to study synapse reinnervation in adult mice lacking the serpin protease nexin-1 (PN-1). PN-1 is a potent endogenous inhibitor of thrombin, trypsin, tissue plasminogen activators (tPAs), and urokinase plasminogen activators. Compared with the wild type, a significant delay in synapse reinnervation was detected in PN-1 knock-out (KO) animals, which was associated with both reduced proliferation and increased apoptosis of Schwann cells. Various factors known to affect Schwann cells were also altered. Fibrin deposits, tPA activity, mature BDNF, and the low-affinity p75 neurotrophin receptor were increased in injured sciatic nerves of mutant mice. To test whether the absence of PN-1 in Schwann cells or in the axon caused delay in reinnervation, PN-1 was overexpressed exclusively in the nerves of PN-1 KO mice. Neuronal PN-1 expression did not rescue the delayed reinnervation. The results suggest that Schwann cell-derived PN-1 is crucial for proper reinnervation through its contribution to the autocrine control of proliferation and survival. Thus, the precise balance between distinct proteases and serpins such as PN-1 can modulate the overall impact on the kinetics of recovery

Newly generated cells are increased in hippocampus of adult mice lacking a serine protease inhibitor

Abstract Background Neurogenesis in the hippocampal dentate gyrus and the subventricular zone occurs throughout the life of mammals and newly generated neurons can integrate functionally into established neuronal circuits. Neurogenesis levels in the dentate gyrus are modulated by changes in the environment (enrichment, exercise), hippocampal-dependent tasks, NMDA receptor (NMDAR) activity, sonic hedgehog (SHH) and/or other factors. Results previously, we showed that Protease Nexin-1 (PN-1), a potent serine protease inhibitor, regulates the NMDAR availability and activity as well as SHH signaling. Compared with wild-type (WT), we detected a significant increase in BrdU-labeled cells in the dentate gyrus of mice lacking PN-1 (PN-1 -/-) both in controls and after running exercise. Patched homologue 1 (Ptc1) and Gli1 mRNA levels were higher and Gli3 down-regulated in mutant mice under standard conditions and to a lesser extent after running exercise. However, the number of surviving BrdU-positive cells did not differ between WT and PN-1 -/- animals. NMDAR availability was altered in the hippocampus of mutant animals after exercise. Conclusion All together our results indicate that PN-1 controls progenitors proliferation through an effect on the SHH pathway and suggest an influence of the serpin on the survival of newly generated neurons through modulation of NMDAR availability.</p

Regulation of brain proteolytic activity is necessary for the in vivo function of NMDA receptors

Serine proteases are considered to be involved in plasticity-related events in the nervous system, but their in vivo targets and the importance of their control by endogenous inhibitors are still not clarified. Here, we demonstrate the crucial role of a potent serine protease inhibitor, protease nexin-1 (PN-1), in the regulation of activity-dependent brain proteolytic activity and the functioning of sensory pathways. Neuronal activity regulates the expression of PN-1, which in turn controls brain proteolytic activity. In PN-1-/- mice, absence of PN-1 leads to increased brain proteolytic activity, which is correlated with an activity-dependent decrease in the NR1 subunit of the NMDA receptor. Correspondingly, reduced NMDA receptor signaling is detected in their barrel cortex. This is coupled to decreased sensory evoked potentials in the barrel cortex and impaired whisker-dependent sensory motor function. Thus, a tight control of serine protease activity is critical for the in vivo function of the NMDA receptors and the proper function of sensory pathways