Prevention of Cell Death by Activation of Hydroxycarboxylic Acid Receptor 1 (GPR81) in Retinal Explants

Abstract

Background: Progressive retinal ganglion cell (RGC) dysfunction and death are common characteristics of retinal neurodegenerative diseases. Recently, hydroxycarboxylic acid receptor 1 (HCA1R, GPR81) was identified as a key modulator of mitochondrial function and cell survival. Thus, we aimed to test whether activation of HCA1R with 3,5-Dihydroxybenzoic acid (DHBA) also promotes RGC survival and improves energy metabolism in mouse retinas. Methods: Retinal explants were treated with 5 mM of the HCA1R agonist, 3,5-DHBA, for 2, 4, 24, and 72 h. Additionally, explants were also treated with 15 mM of L-glutamate to induce toxicity. Tissue survival was assessed through lactate dehydrogenase (LDH) viability assays. RGC survival was measured through immunohistochemical (IHC) staining. Total ATP levels were quantified through bioluminescence assays. Energy metabolism was investigated through stable isotope labeling and gas chromatography-mass spectrometry (GC-MS). Lactate and nitric oxide levels were measured through colorimetric assays. Results: HCA1R activation with 3,5-DHBAincreased retinal explant survival. During glutamate-induced death, 3,5-DHBA treatment also increased survival. IHC analysis revealed that 3,5-DHBA treatment promoted RGC survival in retinal wholemounts. 3,5-DHBA treatment also enhanced ATP levels in retinal explants, whereas lactate levels decreased. No effects on glucose metabolism were observed, but small changes in lactate metabolism were found. Nitric oxide levels remained unaltered in response to 3,5-DHBA treatment. Conclusion: The present study reveals that activation of HCA1R with 3,5-DHBA treatment has a neuroprotective effect specifically on RGCs and on glutamate-induced retinal degeneration. Hence, HCA1R agonist administration may be a potential new strategy for rescuing RGCs, ultimately preventing visual disability.

Evolutionary View on Lactate-Dependent Mechanisms of Maintaining Cancer Cell Stemness and Reprimitivization

“…Lactate has important functions in the nervous system. The extensive investigations of GPR81’s functions in the brain and retina have revealed many new mechanisms of the action of lactate and its role as a signaling molecule in the processes of angiogenesis in the nervous system, the regulation of neuronal excitation, and neuroprotection [ 50 , 51 ].…”

Deletion of GPR81 activates CREB/Smad7 pathway and alleviates liver fibrosis in mice

“…In addition to using the GPR81 KO mice, DHBA, a widely used GPR81 agonist (Vohra et al 2022 ; Ohno et al 2018 ; Tassinari et al 2024 ), was used in the present study to investigate the pathological significance of GPR81. A previous study suggested that the carboxyl group, the 3-hydroxyl group, and the 5-hydroxyl group of DHBA are crucial for the molecular interactions between DHBA and GPR81, and treatment with DHBA inhibited the release of free fatty acid and glycerol in adipocytes, but the antilipolytic effects of DHBA were abolished in GPR81-deficient adipocytes (Liu et al 2012 ).…”

Unlocking the role of lactate: metabolic pathways, signaling, and gene regulation in postmitotic retinal cells

“…Research has revealed the expression of the lactate receptor GPR81 in Müller cells and retinal ganglion cells ( 55 ). Activation of GPR81 shields RGCs from glutamate-induced retinal degeneration and prevents visual impairment ( 81 ). GPR81 activation results in a decrease in cAMP levels in both neural and adipose tissues ( 55 ).…”