Norepinephrine Protects against Methamphetamine Toxicity through β2-Adrenergic Receptors Promoting LC3 Compartmentalization.

Gloria Lazzeri,Paola Lenzi,Gabriele Morucci,Francesco Fornai,Cinzia Fabrizi,Carla L. Busceti,Michela Ferrucci,Francesca Biagioni,Filippo S. Giorgi,Stefano Puglisi-Allegra

doi:10.3390/ijms22137232

Abstract

Norepinephrine (NE) neurons and extracellular NE exert some protective effects against a variety of insults, including methamphetamine (Meth)-induced cell damage. The intimate mechanism of protection remains difficult to be analyzed in vivo. In fact, this may occur directly on target neurons or as the indirect consequence of NE-induced alterations in the activity of trans-synaptic loops. Therefore, to elude neuronal networks, which may contribute to these effects in vivo, the present study investigates whether NE still protects when directly applied to Meth-treated PC12 cells. Meth was selected based on its detrimental effects along various specific brain areas. The study shows that NE directly protects in vitro against Meth-induced cell damage. The present study indicates that such an effect fully depends on the activation of plasma membrane β2-adrenergic receptors (ARs). Evidence indicates that β2-ARs activation restores autophagy, which is impaired by Meth administration. This occurs via restoration of the autophagy flux and, as assessed by ultrastructural morphometry, by preventing the dissipation of microtubule-associated protein 1 light chain 3 (LC3) from autophagy vacuoles to the cytosol, which is produced instead during Meth toxicity. These findings may have an impact in a variety of degenerative conditions characterized by NE deficiency along with autophagy impairment.

Highlights

A bulk of studies indicate that the integrity of norepinephrine (NE) transmission in the brain is fundamental to provide neuroprotection
The present study addresses the following core questions: (i) whether NE directly protects against Meth-induced toxicity; whether such an effect is achieved through specific plasma membrane adrenergic receptors (ARs) activation, or whether NE needs to be taken up in the cell to exert protection; whether NE-induced protection counteracts the derangement of specific autophagy compartments and autophagy flux induced by Meth
Norepinephrine (NE), when applied at different concentrations within the nM range, which corresponds to the Ki for binding at various ARs (0.5 nM, 5 nM, 50 nM), does not affect PC12 cells viability assessed with different methods (Trypan Blue, TB, graph of Supplementary Figure S1A), hematoxylin and eosin

Summary

Introduction

A bulk of studies indicate that the integrity of norepinephrine (NE) transmission in the brain is fundamental to provide neuroprotection. A number of studies hypothesize that in vivo complex neural networks may mediate the protective effects of NE, which would indirectly affect neuronal survival [4,24]. In order to test whether NE directly protects target cells in the present study, we used a model of neurotoxicity, which is well characterized and consists in administering in vitro Meth to PC12 cells [27,28,29]. In this model, the effects of NE were assessed by measuring the amount of cell loss and cell alterations. Once a direct protection was observed, the study proceeds to analyze whether

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Discussion

Conclusion