Biotin-cGMP and -cAMP are able to permeate through the gap junctions of some amacrine cells in the mouse retina despite their large size

Front Ophthalmol (Lausanne). 2024 Jan 15:3:1334602. doi: 10.3389/fopht.2023.1334602. eCollection 2023.

Abstract

Gap junctions transmit electrical signals in neurons and serve metabolic coupling and chemical communication. Gap junctions are made of intercellular channels with large pores, allowing ions and small molecules to permeate. In the mammalian retina, intercellular coupling fulfills many vital functions in visual signal processing but is also implicated in promoting cell death after insults, such as excitotoxicity or hypoxia. Conversely, some studies also suggested a role for retinal gap junctions in neuroprotection. Recently, gap junctions were also advocated as conduits for therapeutic drug delivery in neurodegenerative disorders. This requires the permeation of rather large molecules through retinal gap junctions. However, the permeability of retinal networks for molecules >0.6 kDa has not been tested systematically. Here, we used the cut-loading method and probed gap junctional networks in the mouse retina for their permeability to cGMP and cAMP coupled to Biotin, using the well-characterized tracer Neurobiotin as control. Biotin-cGMP and -cAMP have a molecular weight of >0.8 kDa. We show that they cannot pass the gap junctions of horizontal cells but can permeate through the gap junctions of specific amacrine cells in the inner retina. These amacrine cells do not comprise AII amacrine cells and nitric oxide-releasing amacrine cells but some unknown type. In summary, we show that some retinal gap junctions are large enough to let molecules >0.8 kDa pass, making the intercellular delivery of therapeutic agents - already successfully exploited, for example, in cancer - also feasible in neurodegenerative diseases.

Keywords: amacrine cell; electrical synapse; gap junction; horizontal cell; mouse; retina.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. Funded by the European Union under the action of ERA-NET NEURON (JCT2020:1066 Rethealthsi), financed by the German Federal Ministry of Education and Research (BMBF, 01EW2107 to KD), Volkswagen Foundation (Lichtenberg professorship awarded to IS), Ministry for Science and Culture of Lower Saxony “Simulations Meet Experiments on the Nanoscale: Opening up the Quantum World to Artificial Intelligence (SMART)” (to IS) and “Dynamik auf der Nanoskala: Von kohärenten Elementarprozessen zur Funktionalität (DyNano)” (to IS) and the DFG (RTG 1885/2 Molecular Basis of Sensory Biology; SFB 1372 Magnetoreception and Navigation in Vertebrates, no. 395940726 to KD and IS). We acknowledge support by the Open Access Publishing Fund of the University of Oldenburg. Computational resources for the simulations were provided by the CARL Cluster at the Carl von Ossietzky Universität, Oldenburg, supported by the DFG and the Ministry for Science and Culture of Lower Saxony. The authors also gratefully acknowledge the computing time granted by the Resource Allocation Board and provided on the super-computer Lise and Emmy at NHR@ZIB and NHR@ Göttingen as part of the NHR infrastructure. The calculations for this research were conducted with computing resources under the project nip00058.