Expression profile of multiple secretory phospholipase A2 isoforms in the rat CNS: Enriched expression of sPLA2-IIA in brainstem and spinal cord

Phospholipases A2 (PLA2) are enzymes which cleave the sn-2 ester bond in membrane phospholipids to release free fatty acids and lysophospholipids. The present study aimed to elucidate the expression profile of multiple secretory phospholipase A2 (sPLA2) isoforms in the normal rat CNS with focus on sPLA2-IIA in the brainstem and spinal cord. Quantitative RT-PCR analysis showed that sPLA2-IB expression was low throughout the CNS, sPLA2-IIA expression was high in the brainstem and spinal cord, sPLA2-IIC expression was high in the cerebral neocortex, hippocampus and thalamus/hypothalamus, sPLA2-V expression was high in the olfactory bulb and cerebellum, and sPLA2-X was expressed at very low levels in the normal CNS. Of the isoforms, sPLA2-IIA mRNA expression was highest in the brainstem and spinal cord suggesting that this could be the most relevant isoform in the ascending pain pathway. Western blot analysis showed high level of sPLA2-IIA expression in the brainstem and cervical, thoracic and lumbar spinal segments but low level of expression in other parts of the brain. sPLA2-IIA was localized by immunohistochemistry to the spinal trigeminal and facial motor nuclei and dorsal- and ventral-horns of the spinal cord. The enzyme was found on the endoplasmic reticulum of neuronal cell bodies and small diameter dendrites or dendritic spines at electron microscopy. The expression of sPLA2-IIA in the dorsal horn and spinal trigeminal nucleus is consistent with previous results which showed an important role of CNS sPLA2 in nociceptive transmission.