Lysophosphatidic acid receptors 2 and 3 regulate erythropoiesis at different hematopoietic stages

LPA3 agonist-producing Bacillus velezensis ADS024 is efficacious in multiple neuroinflammatory disease models

Neuroinflammation is a common component of neurological disorders. In the gut-brain-immune axis, bacteria and their metabolites are now thought to play a role in the modulation of the nervous and immune systems which may impact neuroinflammation. In this respect, commensal bacteria of humans have recently been shown to produce metabolites that mimic endogenous G-protein coupled receptor (GPCR) ligands. To date, it has not been established whether plant commensal bacteria, which may be ingested by animals including humans, can impact the gut-brain-immune axis via GPCR agonism. We screened an isopropanol (IPA) extract of the plant commensal Bacillus velezensis ADS024, a non-engrafting live biotherapeutic product (LBP) with anti-inflammatory properties isolated from human feces, against a panel of 168 GPCRs and identified strong agonism of the lysophosphatidic acid (LPA) receptor LPA3. The ADS024 IPA extracted material (ADS024-IPA) did not agonize LPA2, and only very weakly agonized LPA1. The agonism of LPA3 was inhibited by the reversible LPA1/3 antagonist Ki16425. ADS024-IPA signaled downstream of LPA3 through G-protein-induced calcium release, recruitment of β-arrestin, and recruitment of the neurodegeneration-associated proteins 14-3-3γ, ε and ζ but did not recruit the β isoform. Since LPA3 agonism was previously indirectly implicated in the reduction of pathology in models of Parkinson's disease (PD) and multiple sclerosis (MS) by use of the nonselective antagonist Ki16425, and since we identified an LPA3-specific agonist within ADS024, we sought to examine whether LPA3 might indeed be part of a broad underlying mechanism to control neuroinflammation. We tested oral treatment of ADS024 in multiple models of neuroinflammatory diseases using three models of PD, two models of MS, and a model each of amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and chemo-induced peripheral neuropathy (CIPN). ADS024 treatment improved model-specific functional effects including improvements in motor movement, breathing and swallowing, and allodynia suggesting that ADS024 treatment impacted a universal underlying neuroinflammatory mechanism regardless of the initiating cause of disease. We used the MOG-EAE mouse model to examine early events after disease initiation and found that ADS024 attenuated the increase in circulating lymphocytes and changes in neutrophil subtypes, and ADS024 attenuated the early loss of cell-surface LPA3 receptor expression on circulating white blood cells. ADS024 efficacy was partially inhibited by Ki16425 in vivo suggesting LPA3 may be part of its mechanism. Altogether, these data suggest that ADS024 and its LPA3 agonism activity should be investigated further as a possible treatment for diseases with a neuroinflammatory component.

Lysophosphatidic Acid Receptor 3 (LPA3): Signaling and Phosphorylation Sites

LPA3 receptors were expressed in TREx HEK 293 cells, and their signaling and phosphorylation were studied. The agonist, lysophosphatidic acid (LPA), increased intracellular calcium and ERK phosphorylation through pertussis toxin-insensitive processes. Phorbol myristate acetate, but not LPA, desensitizes LPA3-mediated calcium signaling, the agonists, and the phorbol ester-induced LPA3 internalization. Pitstop 2 (clathrin heavy chain inhibitor) markedly reduced LPA-induced receptor internalization; in contrast, phorbol ester-induced internalization was only delayed. LPA induced rapid β-arrestin-LPA3 receptor association. The agonist and the phorbol ester-induced marked LPA3 receptor phosphorylation, and phosphorylation sites were detected using mass spectrometry. Phosphorylated residues were detected in the intracellular loop 3 (S221, T224, S225, and S229) and in the carboxyl terminus (S321, S325, S331, T333, S335, Y337, and S343). Interestingly, phosphorylation sites are within sequences predicted to constitute β-arrestin binding sites. These data provide insight into LPA3 receptor signaling and regulation.

LPA3 Receptor Phosphorylation Sites: Roles in Signaling and Internalization

Lysophosphatidic acid (LPA) type 3 (LPA3) receptor mutants were generated in which the sites detected phosphorylated were substituted by non-phosphorylatable amino acids. Substitutions were made in the intracellular loop 3 (IL3 mutant), the carboxyl terminus (Ctail), and both domains (IL3/Ctail). The wild-type (WT) receptor and the mutants were expressed in T-REx HEK293 cells, and the consequences of the substitutions were analyzed employing different functional parameters. Agonist- and LPA-mediated receptor phosphorylation was diminished in the IL3 and Ctail mutants and essentially abolished in the IL3/Ctail mutant, confirming that the main phosphorylation sites are present in both domains and their role in receptor phosphorylation eliminated by substitution and distributed in both domains. The WT and mutant receptors increased intracellular calcium and ERK 1/2 phosphorylation in response to LPA and PMA. The agonist, Ki16425, diminished baseline intracellular calcium, which suggests some receptor endogenous activity. Similarly, baseline ERK1/2 phosphorylation was diminished by Ki16425. An increase in baseline ERK phosphorylation was detected in the IL3/Ctail mutant. LPA and PMA-induced receptor interaction with β-arrestin 2 and LPA3 internalization were severely diminished in cells expressing the mutants. Mutant-expressing cells also exhibit increased baseline proliferation and response to different stimuli, which were inhibited by the antagonist Ki16425, suggesting a role of LPA receptors in this process. Migration in response to different attractants was markedly increased in the Ctail mutant, which the Ki16425 antagonist also attenuated. Our data experimentally show that receptor phosphorylation in the distinct domains is relevant for LPA3 receptor function.

Lysophosphatidic Acid Receptor 3 Activation Is Involved in the Regulation of Ferroptosis

Ferroptosis, a unique form of programmed cell death trigged by lipid peroxidation and iron accumulation, has been implicated in embryonic erythropoiesis and aging. Our previous research demonstrated that lysophosphatidic acid receptor 3 (LPA3) activation mitigated oxidative stress in progeria cells and accelerated the recovery of acute anemia in mice. Given that both processes involve iron metabolism, we hypothesized that LPA3 activation might mediate cellular ferroptosis. In this study, we used an LPA3 agonist, 1-Oleoyl-2-O-methyl-rac-glycerophosphothionate (OMPT), to activate LPA3 and examine its effects on the ferroptosis process. OMPT treatment elevated anti-ferroptosis gene protein expression, including solute carrier family 7 member 11 (SLC7A11), glutathione peroxidase 4 (GPX4), heme oxygenase-1 (HO-1), and ferritin heavy chain (FTH1), in erastin-induced cells. Furthermore, OMPT reduced lipid peroxidation and intracellular ferrous iron accumulation, as evidenced by C11 BODIPY™ 581/591 Lipid Peroxidation Sensor and FerroOrange staining. These observations were validated by applying LPAR3 siRNA in the experiments mentioned above. In addition, the protein expression level of nuclear factor erythroid 2-related factor (NRF2), a key regulator of oxidative stress, was also enhanced in OMPT-treated cells. Lastly, we verified that LPA3 plays a critical role in erastin-induced ferroptotic human erythroleukemia K562 cells. OMPT rescued the erythropoiesis defect caused by erastin in K562 cells based on a Gly A promoter luciferase assay. Taken together, our findings suggest that LPA3 activation inhibits cell ferroptosis by suppressing lipid oxidation and iron accumulation, indicating that ferroptosis could potentially serve as a link among LPA3, erythropoiesis, and aging.

Lysophosphatidic Acid Receptor 3 Promotes Mitochondrial Homeostasis against Oxidative Stress: Potential Therapeutic Approaches for Hutchinson–Gilford Progeria Syndrome

Lysophosphatidic acid (LPA) is a growth factor-like lipid mediator that regulates various physiological functions via activation of multiple LPA G protein-coupled receptors. We previously reported that LPA suppresses oxidative stress in premature aging Hutchinson-Gilford progeria syndrome (HGPS) patient fibroblasts via its type 3 receptor (LPA₃). Mitochondria have been suggested to be the primary origin of oxidative stress via the overproduction of reactive oxygen species (ROS). Mitochondria are responsible for producing ATP through oxidative phosphorylation (OXPHOS) and have a calcium buffering capacity for the cell. Defects in mitochondria will lead to declined antioxidant capacity and cell apoptosis. Therefore, we aim to demonstrate the regulatory role of LPA₃ in mitochondrial homeostasis. siRNA-mediated depletion of LPA₃ leads to the depolarization of mitochondrial potential (ΔΨm) and cellular ROS accumulation. In addition, the depletion of LPA₃ enhances cisplatin-induced cytochrome C releasing. This indicates that LPA₃ is essential to suppress the mitochondrial apoptosis pathway. LPA₃ is also shown to improve mitochondrial ADP-ATP exchange by enhancing the protein level of ANT2. On the other hand, LPA₃ regulates calcium uptake from the ER to mitochondria via the IP3R1-VDAC1 channel. Moreover, activation of LPA₃ by selective agonist OMPT rescues mitochondrial homeostasis of H₂O₂-induced oxidative stress cells and HGPS patient fibroblasts by improving mitochondrial ΔΨm and OXPHOS. In summary, our findings imply that LPA₃ acts as the gatekeeper for mitochondrial healthiness to maintain cell youth. Furthermore, LPA₃ can be a promising therapeutic target to prevent mitochondrial oxidative stress in aging and HGPS.

Transcriptional regulation of lysophosphatidic acid receptors 2 and 3 regulates myeloid commitment of hematopoietic stem cells

Lysophosphatidic acid (LPA) is one of the lipids identified to be involved in stem cell differentiation. It exerts various functions through activation of G protein-coupled lysophosphatidic acid receptors (LPARs). In previous studies, we have demonstrated that activation of LPA receptor 3 (LPA₃) promotes erythropoiesis of human hematopoietic stem cells (HSCs) and zebrafish using molecular and pharmacological approaches. Our results show that treatment with lysophosphatidic acid receptor 2 (LPA₂) agonist suppressed erythropoiesis, whereas activation of LPA₃ by 1-oleoyl-2-methyl-sn-glycero-3-phosphothionate (2S-OMPT) promoted it, both in vitro and in vivo. Furthermore, we have demonstrated the inhibitory role of LPA₃ during megakaryopoiesis. However, the mechanism underlying these observations remains elusive. In the present study, we suggest that the expression pattern of LPARs may be correlated with the transcriptional factors GATA-1 and GATA-2 at different stages of myeloid progenitors. We determined that manipulation of GATA factors affected the expression levels of LPA₂ and LPA₃ in K562 leukemia cells. Using luciferase assays, we demonstrate that the promoter regions of LPAR2 and LPAR3 genes were regulated by these GATA factors in HEK293T cells. Mutation of GATA-binding sites in these regions abrogated luciferase activity, suggesting that LPA₂ and LPA₃ are regulated by GATA factors. Moreover, physical interaction between GATA factors and the promoter region of LPAR genes was verified in K562 cells using chromatin immunoprecipitation (ChIP) studies. Taken together, our results suggest that balance between LPA₂ and LPA₃ expression, which may be determined by GATA factors, is a regulatory switch for lineage commitment in myeloid progenitors. The expression-level balance of LPA receptor subtypes represents a novel mechanism regulating erythropoiesis and megakaryopoiesis.