Blocking of Connexin-Mediated Communication Promotes Neuroprotection during Acute Degeneration Induced by Mechanical Trauma

Abstract

Accruing evidence indicates that connexin (Cx) channels in the gap junctions (GJ) are involved in neurodegeneration after injury. However, studies using KO animal models endowed apparently contradictory results in relation to the role of coupling in neuroprotection. We analyzed the role of Cx-mediated communication in a focal lesion induced by mechanical trauma of the retina, a model that allows spatial and temporal definition of the lesion with high reproducibility, permitting visualization of the focus, penumbra and adjacent areas. Cx36 and Cx43 exhibited distinct gene expression and protein levels throughout the neurodegeneration progress. Cx36 was observed close to TUNEL-positive nuclei, revealing the presence of this protein surrounding apoptotic cells. The functional role of cell coupling was assessed employing GJ blockers and openers combined with lactate dehydrogenase (LDH) assay, a direct method for evaluating cell death/viability. Carbenoxolone (CBX), a broad-spectrum GJ blocker, reduced LDH release after 4 hours, whereas quinine, a Cx36-channel specific blocker, decreased LDH release as early as 1 hour after lesion. Furthermore, analysis of dying cell distribution confirmed that the use of GJ blockers reduced apoptosis spread. Accordingly, blockade of GJ communication during neurodegeneration with quinine, but not CBX, caused downregulation of initial and effector caspases. To summarize, we observed specific changes in Cx gene expression and protein distribution during the progress of retinal degeneration, indicating the participation of these elements in acute neurodegeneration processes. More importantly, our results revealed that direct control of GJ channels permeability may take part in reliable neuroprotection strategies aimed to rapid, fast treatment of mechanical trauma in the retina.

Calcium signaling and cell proliferation

“…Ca 2+ entry through L-type Ca 2+ channels selectively activates tissuespecific gene expression in neurons, vascular smooth muscle, and cardiomyocytes. Ca 2+ propagated through gap junctions describes direct cell communications [138,139] classically associated with apoptosis of the nervous system [140], transport of secondary messengers like IP 3 , and control cell proliferation via nuclear and ER Ca 2+ fluxes [141,142].…”

Two-color fluorescent analysis of connexin 36 turnover: relationship to functional plasticity

“…In brain injuries, including ischemic events, epilepsy and compression injury, transient increases in neuronal coupling and Cx36 expression are observed (Oguro et al, 2001;Ohsumi et al, 2006;Wang et al, 2012). This coupling has negative consequences for neuron survival as the extent of cell death is greatly reduced in Cx36 knockout animals or when gap junction inhibitors are applied (Talhouk et al, 2008;Paschon et al, 2012;Belousov and Fontes, 2013). The increase in Cx36 expression is driven by type II metabotropic glutamate receptors and involves post-transcriptional mechanisms (Wang et al, 2012).…”

Characterizing the dynamics of three FitzHugh-Nagumo neurons network

“…The operation of the whole nervous system is based on the chemical and electrical synapses [12]. Nowadays, the efforts of researchers go beyond to the simple understanding of the neural systems functions, and researches to discover efficient treatments of neurodegenerative diseases are being carried out [11]. In the recent paper [11], the authors show that the possibility to decoupling neurons can be an efficient strategy to neuroprotection and prevent the process of cell deaths related to the neurodegenerative diseases as Parkinson, Alzheimer, epilepsy, for instance.…”