Multiple steps determine CD73 shedding from RPE: lipid raft localization, ARA1 interaction, and MMP-9 up-regulation

Physiologically, retinal pigment epithelium (RPE) expresses high levels of CD73 in their membrane, converting AMP to immune suppressive adenosine, mediates an anti-inflammatory effect. However, after being exposed to inflammatory factors, RPE rapidly becomes CD73-negative cells, which render RPE's immune suppressive function and accelerate local inflammation. Here, we investigated the mechanism leading to the loss of membrane CD73 in RPE. We found the controversy that when membrane CD73 was significantly diminished in inflammatory RPE, Cd73 mRNA levels were not changed at all. It was further verified that, matrix metalloproteinase-9 (MMP-9) mediated the shedding of CD73 from the cell membrane of inflammatory RPE by catalyzing its K547/F548 site. However, MMP-9 could not catalyze uncomplexed CD73, the interaction of CD73 with adenosine receptor A1 subtype (ARA1) is necessary for being catalyzed by MMP-9. After being treated by LPS and TNF-α, the formation of CD73/ARA1 complex in RPE was verified by co-immunoprecipitation and FRET-based assays. It was also revealed that CD73 need to be localized in lipid rafts to be capable of interacting with ARA1, since CD73/ARA1 interaction and CD73 shedding were completely blocked by the addition of lipid raft synthesis inhibitor. As a conclusion, multiple steps are involved in CD73 shedding in RPE, including up-regulation of MMP-9 activity, localization of CD73 in lipid rafts, and the formation of CD73/ARA1 complex. Lipid rafts committed CD73 with high mobility, shuttled CD73 to ARA1 to form a complex, which was capable of being recognized and catalyzed by MMP-9.

Therapeutic Path to Double Knockout: Investigating the Selective Dual-Inhibitory Mechanisms of Adenosine Receptors A1 and A2 by a Novel Methoxy-Substituted Benzofuran Derivative in the Treatment of Parkinson's Disease

The dual inhibition of adenosine receptors A1 (A₁ AR) and A2 (A_2A AR) has been considered as an efficient strategy in the treatment of Parkinson's disease (PD). This led to the recent development of a series of methoxy-substituted benzofuran derivatives among which compound 3j exhibited dual-inhibitory potencies in the micromolar range. Therefore, in this study, we seek to resolve the mechanisms by which this novel compound elicits its selective dual targeting against A₁ AR and A_2A AR. Unique to the binding of 3j in both proteins, from our findings, is the ring-ring interaction elicited by _A1Phe275 (→ _A2Phe170) with the benzofuran ring of the compound. As observed, this π-stacking interaction contributes notably to the stability of 3j at the active sites of A₁ and A_2A AR. Besides, conserved active site residues in the proteins such as _A1Ala170 (→ _A2Ala65), _A1Ile173 (→ _A2Ile68), _A1Val191 (→ _A2Val86), _A1Leu192 (→ _A2Leu87), _A1Ala195 (→ _A2Ala90), _A1Met284 (→ _A2Met179), _A1Tyr375 (→ _A2Tyr369), _A1Ile378 (→ _A2Ile372), and _A1His382 (→ _A2His376) were commonly involved with other ring substituents which further complement the dual binding and stability of 3j. This reflects a similar interaction mechanism that involved aromatic (π) interactions. Consequentially, vdW energies contributed immensely to the dual binding of the compound, which culminated in high ΔG_binds that were homogenous in both proteins. Furthermore, 3j commonly disrupted the stable and compact conformation of A₁ and A_2A AR, coupled with their active sites where Cα deviations were relatively high. Ligand mobility analysis also revealed that both compounds exhibited a similar motion pattern at the active site of the proteins relative to their optimal dual binding. We believe that findings from this study with significantly aid the structure-based design of highly selective dual-inhibitors of A₁ and A_2A AR.

Antidepressant effects of SY-2476: A caffeine derivative's role in A1/A2A gene expression modulation in corticosterone-induced depressed rats

Depression is a pervasive mood disorder that continues to challenge researchers and clinicians worldwide. Caffeine and its derivatives have been studied for their neuroprotective and antidepressant effect. Current study aimed to explore the potential antidepressant effect of a caffeine derivative, Sy-2476 [4-(1, 3, 7-trimethyl-2, 6-dioxo-2, 3, 6, 7-tetrahydro-1H-purin-8-yl) benzo nitrile], in corticosterone-induced rat model of depression. Depression-like behaviour in rats was induced by administering 20 mg/kg hydrocortisone s.c for 21 days. Behavioural studies evaluated the potential antidepressant effect of caffeine derivative Sy-2476, its effect on cortisol levels, modulation of A1/A2A receptors mRNA expression and antioxidant assays. Treatment of rats with Sy-2476 exhibited robust antidepressant-like effects in corticosterone-exposed rats by increasing sucrose preference (p = 0.0002) while reducing immobility time (p = 0.0118) in the forced swim test. Sy-2476 also reduced lipid peroxidation and increased the level of antioxidant enzymes, including glutathione, catalase, and superoxide dismutase. Moreover, Sy-2476 significantly lowered cortisol levels (p = 0.0019) and up-regulated mRNA expression of A1 (p = 0.0001) and A2A receptors (p = 0.0016) compared to the corticosterone-only treated group. In conclusion, Sy-2476 showed an antidepressant effect primarily by suppressing serum cortisol levels, modulating the expression of adenosine receptors, and exhibiting antioxidant properties.

Adenosine kinase protects against acetaminophen-induced acute liver injury by activating autophagy in hepatocytes

Acute liver injury (ALI) is a common life-threatening condition with a high mortality rate due to liver disease-related death. However, current therapeutic interventions for ALI remain ineffective, and the development of effective novel therapies is urgently needed. Liver samples from patients with drug-induced ALI were collected to detect adenosine kinase (ADK) expression. Male C57BL/6 J mice, hepatocyte-specific ADK knockout (ADKHKO) mice, and their controls (ADKf/f) were exposed to acetaminophen (APAP) and other treatments to investigate the mechanisms of APAP-related ALI. ADK expression was significantly decreased in APAP-injured livers. Hepatocyte-specific ADK deficiency exacerbated APAP-induced ALI, while a gain-of-function approach delivering AAV-ADK, markedly alleviated APAP-induced ALI, as indicated by changes in alanine aminotransferases (ALT) levels, aspartate aminotransferase (AST) levels, neutrophil infiltration and hepatocyte death. This study showed that ADK played a critical role in ALI by activating autophagy through two signaling pathways, the adenosine monophosphate-activated protein kinase (AMPK)-mTOR pathway and the adenosine receptor A1 (ADORA1)-Akt-mTOR pathway. Furthermore, we found that metformin upregulated ADK expression in hepatocytes and protected against APAP-induced ALI. These results demonstrate that ADK is critical in protecting against APAP-induced ALI and that developing therapeutics targeting ADK-adenosine-ADORA1 is a new approach for ALI treatment. Metformin is a potential candidate for preventing ALI by upregulating ADK.

Protective effects of caffeine against palmitate-induced lipid toxicity in primary rat hepatocytes is associated with modulation of adenosine receptor A1 signaling

BACKGROUND

Epidemiological evidence has shown an association between coffee consumption and reduced risk for chronic liver diseases, including metabolic-dysfunction-associated liver disease (MALFD). Lipotoxicity is a key cause of hepatocyte injury during MAFLD. The coffee component caffeine is known to modulate adenosine receptor signaling via the antagonism of adenosine receptors. The involvement of these receptors in the prevention of hepatic lipotoxicity has not yet been explored. The aim of this study was to explore whether caffeine protects against palmitate-induced lipotoxicity by modulating adenosine receptor signaling.

METHODS

Primary hepatocytes were isolated from male rats. Hepatocytes were treated with palmitate with or without caffeine or 1,7DMX. Lipotoxicity was verified using Sytox viability staining and mitochondrial JC-10 staining. PKA activation was verified by Western blotting. Selective (ant)agonists of A1AR (DPCPX and CPA, respectively) and A2AR (istradefyline and regadenoson, respectively), the AMPK inhibitor compound C, and the Protein Kinase A (PKA) inhibitor Rp8CTP were used. Lipid accumulation was verified by ORO and BODIPY 453/50 staining.

RESULTS

Caffeine and its metabolite 1,7DMX prevented palmitate-induced toxicity in hepatocytes. The A1AR antagonist DPCPX also prevented lipotoxicity, whereas both the inhibition of PKA and the A1AR agonist CPA (partially) abolished the protective effect. Caffeine and DPCPX increased lipid droplet formation only in palmitate-treated hepatocytes and decreased mitochondrial ROS production.

CONCLUSIONS

The protective effect of caffeine against palmitate lipotoxicity was shown to be dependent on A1AR receptor and PKA activation. Antagonism of A1AR also protects against lipotoxicity. Targeting A1AR receptor may be a potential therapeutic intervention with which to treat MAFLD.

Adenosine receptor A1 enhanced mitochondrial biogenesis and exerted neuroprotection after cerebral ischemia through PGC-1α

Ischemic stroke is a common cause of morbidity and mortality worldwide. The current treatment fails to achieve satisfactory results, because interventional therapy as first-line treatment management has a strict time window. In recent years, a large number of studies have confirmed that adenosine, as an inhibitory neurotransmitter, has a protective effect on cerebral ischemic injury. Nevertheless, direct administration of adenosine has many side effects. Previous studies showed that adenosine exerted neuroprotective effects mainly through adenosine receptor A1 (A1 receptor). Therefore, further study on the mechanism of A 1 receptor induced neuroprotection may find new targets for stroke treament. Mitochondrial biogenesis (MB) is a therapeutic target for ischemic stroke, and the nuclear-encoded peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α) is a major regulator of MB. However, the influence of A1 receptor on MB and PGC-1α is unclear. In this study, using the middle cerebral artery occlusion (MCAO) model of mice, we evaluated the temporal and spatial effects of A1 receptor after ischemic stroke and verified the neuroprotection of A1 receptor. Neurological scores were used to assess functional changes in mice. At the same time, we observed the effect of activating A1 receptor on MB and PGC-1α, and the effect of knockdown PGC-1α on A1 receptor induced MB in vitro. WB and immunofluorescence were used to detect relevant indicators of MB. In addition, we downregulated PGC-1α in vivo to observe the effects on A1 receptor induced MB and neuroprotection. The findings indicated that A1 receptor was increased and mainly expressed on neurons in the penumbra, further activated A1 receptor after stroke had neuroprotection. In vitro, activation of A1 promotes MB and increases the expression level of PGC-1α, while downregulation of PGC-1α partially reverses the effect of A1 receptor after OGD/R. Down regulation of PGC-1α in the penumbra neurons can reverse the effects of activation of A1 receptor on MB and neuroprotection. Taken together, these findings indicated that A1receptor promotes MB and improves neurological function after ischemic stroke via PGC-1α.