Modulation of calcineurin activity in mouse brain by chronic oral administration of cyclosporine A

Ca2+ -Calmodulin-Calcineurin Signaling Modulates α-Synuclein Transmission

BACKGROUND

The intercellular transmission of pathogenic proteins plays a crucial role in the progression of neurodegenerative diseases. Previous research has shown that the neuronal uptake of such proteins is activity-dependent; however, the detailed mechanisms underlying activity-dependent α-synuclein transmission in Parkinson's disease remain unclear.

OBJECTIVE

To examine whether α-synuclein transmission is affected by Ca2+ -calmodulin-calcineurin signaling in cultured cells and mouse models of Parkinson's disease.

METHODS

Mouse primary hippocampal neurons were used to examine the effects of the modulation of Ca2+ -calmodulin-calcineurin signaling on the neuronal uptake of α-synuclein preformed fibrils. The effects of modulating Ca2+ -calmodulin-calcineurin signaling on the development of α-synuclein pathology were examined using a mouse model injected with α-synuclein preformed fibrils.

RESULTS

Modulation of Ca2+ -calmodulin-calcineurin signaling by inhibiting voltage-gated Ca2+ channels, calmodulin, and calcineurin blocked the neuronal uptake of α-synuclein preformed fibrils via macropinocytosis. Different subtypes of voltage-gated Ca2+ channel differentially contributed to the neuronal uptake of α-synuclein preformed fibrils. In wild-type mice inoculated with α-synuclein preformed fibrils, we found that inhibiting calcineurin ameliorated the development of α-synuclein pathology.

CONCLUSION

Our data suggest that Ca2+ -calmodulin-calcineurin signaling modulates α-synuclein transmission and has potential as a therapeutic target for Parkinson's disease. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Calcineurin and Its Role in Synaptic Transmission

Calcineurin (CaN) is a serine/threonine phosphatase widely expressed in different cell types and structures including neurons and synapses. The most studied role of CaN is its involvement in the functioning of postsynaptic structures of central synapses. The role of CaN in the presynaptic structures of central and peripheral synapses is less understood, although it has generated a considerable interest and is a subject of a growing number of studies. The regulatory role of CaN in synaptic vesicle endocytosis in the synapse terminals is actively studied. In recent years, new targets of CaN have been identified and its role in the regulation of enzymes and neurotransmitter secretion in peripheral neuromuscular junctions has been revealed. CaN is the only phosphatase that requires calcium and calmodulin for activation. In this review, we present details of CaN molecular structure and give a detailed description of possible mechanisms of CaN activation involving calcium, enzymes, and endogenous and exogenous inhibitors. Known and newly discovered CaN targets at pre- and postsynaptic levels are described. CaN activity in synaptic structures is discussed in terms of functional involvement of this phosphatase in synaptic transmission and neurotransmitter release.

Enzymatic and thermodynamic analysis of calcineurin inhibition by RCAN1

Calcineurin (CN) is the target of the immunophilin-immunosuppressant complex, cyclophilin/cyclosporin A (CyP/CsA). RCAN1 has recently been shown to be an endogenous regulator of CN activity. We determined the enzymatic and thermodynamic aspects of CN inhibition by RCAN1. The IC50 values of isoforms RCAN1-1L and RCAN1-4 for CN were 2.7 μM and 2.6 μM, respectively. Two deletions in the CN catalytic subunit, one a deletion of Val314 in the Loop7 domain (ΔV314) and the other in the autoinhibitory domain (CNAabc), increased the sensitivity of CN to inhibition by RCAN1-1L. The IC50s of RCAN1-1L and RCAN1-4 for CN in homogenates of mouse brain were 141 nM and 100 nM, respectively. Using isothermal titration calorimetry (ITC), we found that the RCAN1-1L/CN or CyP/CsA/CN interactions were exothermic with a dissociation constant of 0.46 μM or 0.17 μM, respectively. Our ITC results show that the interactions between CN and its two inhibitors were both characterized by a favorable binding enthalpy change. We also confirmed that overexpression of RCAN1-1L could inhibit the transcriptional activation of an NFAT-dependent promoter in response to PMA and ionomycin by inhibiting CN activity in HEK293T cells. Our data should contribute to our understanding of the regulation of CN activity by endogenous inhibitors.