Inhibition of Protease-Activated Receptor 1 Does not Affect Dendritic Homeostasis of Cultured Mouse Dentate Granule Cells

Abstract

Protease-activated receptors (PARs) are widely expressed in the central nervous system (CNS). While a firm link between PAR1-activation and functional synaptic and intrinsic neuronal properties exists, studies on the role of PAR1 in neural structural plasticity are scarce. The physiological function of PAR1 in the brain remains not well understood. We here sought to determine whether prolonged pharmacologic PAR1-inhibition affects dendritic morphologies of hippocampal neurons. To address this question we employed live-cell microscopy of mouse dentate granule cell dendrites in 3-week old entorhino-hippocampal slice cultures prepared from Thy1-GFP mice. A subset of cultures were treated with the PAR1-inhibitor SCH79797 (1 μM; up to 3 weeks). No major effects of PAR1-inhibition on static and dynamic parameters of dentate granule cell dendrites were detected under control conditions. Granule cells of PAR1-deficient slice cultures showed unaltered dendritic morphologies, dendritic spine densities and excitatory synaptic strength. Furthermore, we report that PAR1-inhibition does not prevent dendritic retraction following partial deafferentation in vitro. Consistent with this finding, no major changes in PAR1-mRNA levels were detected in the denervated dentate gyrus (DG). We conclude that neural PAR1 is not involved in regulating the steady-state dynamics or deafferentation-induced adaptive changes of cultured dentate granule cell dendrites. These results indicate that drugs targeting neural PAR1-signals may not affect the stability and structural integrity of neuronal networks in healthy brain regions.

Denervated mouse CA1 pyramidal neurons express homeostatic synaptic plasticity following entorhinal cortex lesion

“…Previous research revealed that in vitro entorhinal cortex lesion (ECL) of mouse organotypic entorhino-hippocampal slice cultures induced homeostatic synaptic plasticity of excitatory synapses on dentate granule cells (Vlachos et al, 2012;Lenz et al, 2019). These functional changes depended on cytokine signaling (Becker et al, 2015) and involved the structural remodeling of denervated dendrites (Vlachos et al, 2012(Vlachos et al, , 2013bSchuldt et al, 2016;Willems et al, 2016;Bissen et al, 2021), similar to what is observed after in vivo ECL (Vuksic et al, 2011). Moreover, the induction of homeostatic synaptic plasticity was demonstrated to affect the postlesional recovery of dendritic spine numbers (Vlachos et al, 2013b).…”

Protease Activated Receptor 2 (PAR2) Induces Long-Term Depression in the Hippocampus through Transient Receptor Potential Vanilloid 4 (TRPV4)

“…For example low concentrations of thrombin, or a specific PAR1-agonist, improve the ability of neurons to express synaptic plasticity without inducing LTP per se ( Maggio et al, 2013b , 2014 ). Thus, while in a recent study we were not able to detect adverse effects of prolonged PAR1-inhibition on dendritic plasticity of neurons ( Schuldt et al, 2016 ), it is conceivable that pharmacological inhibition of PAR1 may not only exert positive effects on neural plasticity.…”

Homeostatic effects of coagulation protease‐dependent signaling and protease activated receptors

“…These and other studies indicate that PAR1 inhibition is beneficial in individuals with neuronal diseases associated with breakdown of the blood-brain barrier and/or increased PAR1 activity [74]. Importantly, long-term PAR1 inhibition has no effect on the physiological neuronal function in vitro [75], implying that PAR1 inhibition in the absence of neurological disease is non-toxic. This finding is of clinical relevance considering the advent of small molecule PAR-modulating drugs in clinical use.…”