title: The P2X7 receptor links mechanical strain to cytokine IL-6 up-regulation and release in neurons and astrocytes.
abstract: Mechanical strain in neural tissues can lead to the up-regulation and release of multiple cytokines including interleukin 6 (IL-6). In the retina, the mechanosensitive release of ATP can autostimulate P2X7 receptors on both retinal ganglion cell neurons and optic nerve head astrocytes. Here, we asked whether the purinergic signaling contributed to the IL-6 response to increased intraocular pressure (IOP) in vivo, and stretch or swelling in vitro. Rat and mouse eyes were exposed to non-ischemic elevations in IOP to 50-60 mmHg for 4 h. A PCR array was used to screen cytokine changes, with quantitative (q)PCR used to confirm mRNA elevations and immunoblots used for protein levels. P2X7 antagonist Brilliant Blue G (BBG) and agonist (4-benzoyl-benzoyl)-ATP (BzATP) were injected intravitreally. ELISA was used to quantify IL-6 release from optic nerve head astrocytes or retinal ganglion cells. Receptor identity was confirmed pharmacologically and in P2X7-/-mice, acute elevation of IOP altered retinal expression of multiple cytokine genes. Elevation of IL-6 was greatest, with expression of IL1rn, IL24, Tnf, Csf1, and Lif also increased more than twofold, while expression of Tnfsf11, Gdf9, and Tnfsf4 were reduced. qPCR confirmed the rise in IL-6 and extracellular ATP marker ENTPD1, but not pro-apoptotic genes. Intravitreal injection of P2X7 receptor antagonist BBG prevented the pressure-dependent rise in IL-6 mRNA and protein in the rat retina, while injection of P2X7 receptor agonist BzATP was sufficient to elevate IL-6 expression. IOP elevation increased IL-6 in wild-type but not P2X7R knockout mice. Application of mechanical strain to isolated optic nerve head astrocytes increased IL-6 levels. This response was mimicked by agonist BzATP, but blocked by antagonists BBG and A839977. Stretch or BzATP led to IL-6 release from both astrocytes and isolated retinal ganglion cells. The mechanosensitive up-regulation and release of cytokine IL-6 from the retina involves the P2X7 receptor, with both astrocytes and neurons contributing to the response.
authors.affiliation: Department of Anatomy and Cell Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Wennan
authors.initials: W
authors.lastname: Lu
authors.affiliation: Department of Anatomy and Cell Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.|Department of Orthodontics, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Farraj
authors.initials: F
authors.lastname: Albalawi
authors.affiliation: Department of Anatomy and Cell Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.|Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pennsylvania, USA.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Beckel
authors.affiliation: Department of Anatomy and Cell Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Jason C
authors.initials: JC
authors.lastname: Lim
authors.affiliation: Department of Ophthalmology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Alan M
authors.initials: AM
authors.lastname: Laties
authors.affiliation: Department of Anatomy and Cell Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.|Department of Ophthalmology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.|Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Claire H
authors.initials: CH
authors.lastname: Mitchell
mesh_terms: D000255:Adenosine Triphosphate / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D007267:Injections; D015850:Interleukin-6 / Q000235:genetics / Q000502:physiology*; D007429:Intraocular Pressure; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000378:metabolism*; D009900:Optic Nerve / Q000473:pathology; D058911:Purinergic P2X Receptor Agonists / Q000008:administration & dosage / Q000494:pharmacology; D058920:Purinergic P2X Receptor Antagonists / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans; D017207:Rats, Sprague-Dawley; D058486:Receptors, Purinergic P2X7 / Q000235:genetics / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000187:drug effects; D015854:Up-Regulation / Q000235:genetics; D014822:Vitreous Body
chemical_list: D015850:Interleukin-6; D058911:Purinergic P2X Receptor Agonists; D058920:Purinergic P2X Receptor Antagonists; D058486:Receptors, Purinergic P2X7; C577686:interleukin-6, mouse; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate
keywords: 
  IOP
  ; P2X7; astrocytes; cytokines; mechanical strain; retina