Divalent metal modulation of Japanese flounder (Paralichthys olivaceus) purinergic P2X7 receptor

Animal Models for the Investigation of P2X7 Receptors

The P2X7 receptor is a trimeric ligand-gated cation channel activated by extracellular adenosine 5'-triphosphate. The study of animals has greatly advanced the investigation of P2X7 and helped to establish the numerous physiological and pathophysiological roles of this receptor in human health and disease. Following a short overview of the P2X7 distribution, roles and functional properties, this article discusses how animal models have contributed to the generation of P2X7-specific antibodies and nanobodies (including biologics), recombinant receptors and radioligands to study P2X7 as well as to the pharmacokinetic testing of P2X7 antagonists. This article then outlines how mouse and rat models have been used to study P2X7. These sections include discussions on preclinical disease models, polymorphic P2X7 variants, P2X7 knockout mice (including bone marrow chimeras and conditional knockouts), P2X7 reporter mice, humanized P2X7 mice and P2X7 knockout rats. Finally, this article reviews the limited number of studies involving guinea pigs, rabbits, monkeys (rhesus macaques), dogs, cats, zebrafish, and other fish species (seabream, ayu sweetfish, rainbow trout and Japanese flounder) to study P2X7.

Developmental cadmium exposure disrupts zebrafish vestibular calcium channels interfering with otolith formation and inner ear function

Dizziness or balance problems are estimated to affect approximately 3.3 million children aged three to 17 years. These disorders develop from a breakdown in the balance control system and can be caused by anything that affects the inner ear or the brain, including exposure to environmental toxicants. One potential environmental toxicant linked to balance disorders is cadmium, an extremely toxic metal that occurs naturally in the earth's crust and is released as a byproduct of industrial processes. Cadmium is associated with balance and vestibular dysfunction in adults exposed occupationally, but little is known about the developmental effects of low-concentration cadmium exposure. Our findings indicate that zebrafish exposed to 10-60 parts per billion (ppb) cadmium from four hours post-fertilization (hpf) to seven days post-fertilization (dpf) exhibit abnormal behaviors, including pronounced increases in auditory sensitivity and circling behavior, both of which are linked to reductions in otolith growth and are rescued by the addition of calcium to the media. Pharmacological intervention shows that agonist-induced activation of the P2X calcium ion channel in the presence of cadmium restores otolith size. In conclusion, cadmium-induced ototoxicity is linked to vestibular-based behavioral abnormalities and auditory sensitivity following developmental exposure, and calcium ion channel function is associated with these defects.

Functional characterization of purinergic P2Y2 and P2Y12 receptors involved in Japanese flounder (Paralichthys olivaceus) innate immune responses

G-protein-coupled P2Y receptors activated by extracellular nucleotides play important roles under different physiological and pathophysiological conditions in mammals. To investigate the immunological relevance of P2Y receptors in fish, we identified and characterized the P2Y₂ and P2Y₁₂ receptors in Japanese flounder Paralichthys olivaceus. The P. olivaceus P2Y₂ and P2Y₁₂ receptors harbor seven transmembrane domains but share only 24% sequence identity. Real-time PCR analysis revealed the constitutive but unequal mRNA expression pattern of P2Y₂R and P2Y₁₂R in normal Japanese flounder tissues with the dominant expression of P2Y₂R in head kidney and blood and P2Y₁₂R in hepatopancreas. In addition, the expression of P2Y₂ and P2Y₁₂ receptors was markedly modulated by PAMPs stimulation and Edwardsiella tarda infection. Furthermore, blockage of P2Y₁₂R potently increased ADP-activated pro-inflammatory cytokine IL-1beta gene expression in the head kidney macrophages (HKMs). Moreover, inhibition of P2Y₂ and P2Y₁₂ receptor activity with their respective potent antagonists significantly altered some of the LPS-induced pro-inflammatory cytokine gene expression in the HKMs. However, blockade of P2Y₁₂R did not affect the poly(I:C)-induced pro-inflammatory cytokine gene expression examined in the HKMs. Collectively, we have for the first time reported the role of purinergic P2Y₂ and P2Y₁₂ receptors in fish innate immunity. Our findings have also addressed the importance of extracellular ATP and its metabolites in fish innate immune responses.