Dual Properties of Lactate in Müller Cells: The Effect of GPR81 Activation

Abstract

Citation: Vohra R, Aldana BI, Waagepetersen H, Bergersen LH, Kolko M. Dual properties of lactate in Müller cells: the effect of GPR81 activation. Invest Ophthalmol Vis Sci. 2019;60:999-1008. https://doi.org/ 10.1167/iovs.18-25458PURPOSE. Besides being actively metabolized, lactate may also function as a signaling molecule by activation of the G-protein-coupled receptor 81 (GPR81). Thus, we aimed to characterize the metabolic effects of GPR81 activation in Müller cells.METHOD. Primary Müller cells from mice were treated with and without 10 mM L-lactate in the presence or absence of 6 mM glucose. The effects of lactate receptor GPR81 activation were evaluated by the addition of 5 mM 3,5-DHBA (3,5-dihydroxybenzoic acid), a GPR81 agonist. Western blot analyses were used to determine protein expression of GPR81. Cell survival was assessed through 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) viability assays. Lactate release was quantified by commercially available lactate kits. 13 Clabeling studies via mass spectroscopy and Seahorse analyses were performed to evaluate metabolism of lactate and glucose, and mitochondrial function. Finally, Müller cell function was evaluated by measuring glutamate uptake.RESULTS. The lactate receptor, GPR81, was upregulated during glucose deprivation. Treatment with a GPR81 agonist did not affect Müller cell survival. However, GPR81 activation diminished lactate release allowing lactate to be metabolized intracellularly. Furthermore, GPR81 activation increased metabolism of glucose and mitochondrial function. Finally, maximal glutamate uptake decreased in response to GPR81 activation during glucose deprivation.CONCLUSIONS. The present study revealed dual properties of lactate via functioning as an active metabolic energy substrate and a regulatory molecule by activation of the GPR81 receptor in primary Müller cells. Thus, combinational therapy of lactate and GPR81 agonists may be of future interest in maintaining Müller cell survival, ultimately leading to increased resistance toward retinal neurodegeneration.

Hydroxycarboxylic Acid Receptor 1 and Neuroprotection in a Mouse Model of Cerebral Ischemia-Reperfusion

“…While lactate receptor agonists have been tested using several in vitro paradigms (Dvorak et al, 2012;Liu et al, 2012;Bozzo et al, 2013;Lauritzen et al, 2014;Castillo et al, 2015;Herrera-Lopez and Galvan, 2018;Vardjan et al, 2018;de Castro Abrantes et al, 2019;Vohra et al, 2019), their effects have been only recently tested in the central nervous system with unclear results (Lev-Vachnish et al, 2019;Scavuzzo et al, 2020). To further investigate in this direction and shed some light on a presumable dual protective effect of lactate, we tested if HCAR1 stimulation could provide neuroprotection when administered in vivo in a mouse model of transient hypoxiaischemia.…”

Renormalization of metabolic coupling treats age-related degenerative disorders: an oxidative RPE niche fuels the more glycolytic photoreceptors

“…Various degenerative conditions such as glaucoma and diabetic retinopathy are typically associated with the death of retinal ganglion cells (RGCs). This cell death is prevented by MCs, which have been shown to require lactate for proper function and health [ 19 ]. Evidence has suggested that this lactate consumption is preferential to glucose, and that MCs can even convert lactate to glycogen as a storage mechanism, regulating overall lactate levels in the retina as a whole [ 20 ].…”

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

“…Metabolic mapping of [U- 13 C]glucose and [U- 13 C]lactate in the retina using GC-MS was performed as previously described [21][22][23]37,38]. Briefly, retinal extracts were reconstituted in water, acidified to pH 1-2 with HCl, and evaporated to dryness under nitrogen flow.…”

“…Aerobic glycolysis is the process of glucose breakdown to pyruvate and/or lactate and two ATP molecules that account for 80-96% of total glucose consumption in the retina [19,20]. Both lactate and pyruvate are known retinal energy sources [21][22][23][24][25], which can be further metabolized in the vast number of retinal mitochondria [26,27], where most ATP is produced through oxidative phosphorylation after the tricarboxylic (TCA) cycle.…”

“…In addition, lactate is the endogenous ligand for HCA 1 R, and while plasma levels of lactate in other tissues of the body are too low to activate HCA 1 R [2] (EC 50 : 1-5 mmol/L [28]), the retinal levels of lactate reach between 5-50 mmol/L [29][30][31], providing sufficient activation of HCA 1 R. Lactate treatment of retinal cells in culture has also been shown to exhibit various protective effects, resulting in improved Müller glia function measured through kinetic uptake of glutamate and increased survival of both cultured Müller glia and RGCs in healthy and diseased experimental setups in the presence and absence of glucose, respectively [21,23]. Moreover, cultured Müller glia have also revealed increased glucose metabolism and mitochondrial function in response to HCA 1 R activation with 3,5dihydroxybenzoic acid (DHBA) [22]. Similarly, HCA 1 R-silenced BxPC3 cells displayed reduced mitochondrial activity and cell survival [32].…”