Expression and location of mRNAs encoding multiple forms of secretory phospholipase A sub(2) in the rat retina

Low-molecular-weight secretory phospholipases A sub(2) (sPLA sub(2)s) are a subgroup of PLA sub(2)s, which are secreted, bind to receptors, and may act as intercellular signaling modulators. At least 10 different groups have been characterized in mammals, and there is expanding evidence of the significance of sPLA sub(2)s in neuronal signaling and survival [Kolko et al. (1996) J. Biol. Chem. 271: 32722-32728]. To date, no retinal sPLA sub(2)s have been cloned or characterized. We evaluated the existence and abundance of sPLA sub(2) subtypes in rat retina and explored their possible involvement in light-induced retinal damage. We designed primers to identify the sPLA sub(2)s in rat retina, based on known sequences of sPLA sub(2)-specific mRNAs in other tissues. RNA was isolated from rat retina, and cDNA was produced and used for PCR cloning to identify the novel subtypes of sPLA sub(2). Our study revealed the presence of mRNAs encoding sPLA sub(2)-IB, -X, -V, -IIE, -IIA, and -IIF in the retina, and quantification by real-time PCR revealed different abundances of the sPLA sub(2)s. We showed a time- dependent gene induction of sPLA sub(2)-X, -IB, and -V in light-induced retinal damage. We further explored the location of sPLA sub(2)-IB by in situ hybridization and immunohistochemistry. This study is the first to reveal the presence, abundance, and induction of mRNAs encoding sPLA sub(2)s in rat retina. We suggest that these enzymes are themselves intercellular signaling modulators of retinal cell function and perhaps also of retinal degeneration.