Switching of Platelet-activating Factor Acetylhydrolase Catalytic Subunits in Developing Rat Brain

Abstract

In a previous study, we demonstrated that Plateletactivating Factor (PAF) acetylhydrolase purified from bovine brain cortical cytosol consists of two mutually homologous catalytic subunits (␣1 and ␣2) and one putative regulatory ␤ subunit. The latter is a product of the LIS1 gene, which is defective in the Miller-Dieker syndrome, a form of lissencephaly. In this study, we examined the expression patterns of these three subunits in the developing rat brain. All three subunits were expressed in embryonic brain, whereas only ␣2 and ␤ subunit were detected in the adult brain by Western blotting. Biochemical analyses revealed that the ␣1/␣2 heterodimer and ␣2/␣2 homodimer are major catalytic units of embryonic and adult brain PAF acetylhydrolases, respectively. The ␣1 transcript and protein were detected predominantly in embryonic and postnatal neural tissues, such as the brain and spinal cord. Furthermore, we found using primary cultured cells isolated from neonatal rat brain that ␣1 protein were expressed only in neurons but not in glial cells and fibroblasts. In contrast, ␣2 and ␤ transcripts and proteins were detected both in neural and non-neural tissues, and their expression level was almost constant from fetal stages through adulthood. These results indicate that ␣1 expression is restricted to actively migrating neurons in rats and that switching of catalytic subunits from the ␣1/␣2 heterodimer to the ␣2/␣2 homodimer occurred in these cells during brain development, suggesting that PAF acetylhydrolase plays a role(s) in neuronal migration. Platelet-activating factor (PAF)1 is a potent pro-inflammatory phospholipid produced by leukocytes, platelets, endothelial cells, and some neural cells. Mammalian brains contain significant amounts of PAF, which may act as a synapse messenger and transcription inducer of the early-response genes c-fos and c-jun (1). PAF has also been implicated as a messenger in long term potentiation, a cellular model of memory formation (2).PAF is inactivated by a specific enzyme, PAF acetylhydrolase, which removes the acetyl moiety at the sn-2 position of the glycerol backbone (3). Mammalian PAF acetylhydrolase is classified into two types (4), plasma (extracellular) and tissue (intracellular). The former is a 43-kDa monomeric enzyme that effectively abolishes the inflammatory effects of PAF on leukocytes and the vasculature, indicating it is involved in maintaining plasma PAF at certain levels (5). Recently, we succeeded in purifying and cloning intracellular PAF acetylhydrolases. Tissue cytosol contains at least two types of intracellular PAF acetylhydrolase, isoforms Ib and II (6). Isoform II (PAF acetylhydrolase(II)) is a 40-kDa monomer, and its amino acid sequence exhibits 41% identity with that of plasma PAF acetylhydrolase (5, 7, 8), whereas isoform Ib is a heterotrimeric enzyme composed of ␣1, ␣2, and ␤ subunits (6). So far, cDNAs for the three subunits of PAF acetylhydrolase(Ib) have been cloned from the cow (9 -11), human (12, 13), mouse (14), and rat (15). Molecular cloning has...

Anti-apoptotic Actions of the Platelet-activating Factor Acetylhydrolase I α2 Catalytic Subunit

“…PAF-AH I ␣ 2 /␣ 2 is known to hydrolyze PAF more efficiently than ␣ 1 /␣ 1 homodimers, and it is likely that reducing PAF-AH ␣ 1 coincident with PAF-AH ␣ 2 induction would promote more rapid formation of ␣ 2 /␣ 2 homodimers, enhance PAF hydrolysis, and increase cell survival. Most interestingly, this phenomenon models the graded reduction in ␣ 1 observed over the course of cerebral development by changing the predominant PAF-AH I catalytic composition from ␣ 1 /␣ 2 heterodimers in embryonic central nervous system to ␣ 2 /␣ 2 homodimers in adult brain (51). Our data suggest that this shift may render adult brain more resistant to PAF challenge than embryonic brain.…”

LIS1—no more no less

“…46,47 A homolog for the catalytic subunit in Drosophila was identified. However, it lacks both enzymatic activity and the ability to interact with LIS1.…”

Chronic Cerebral Hypoperfusion Induced Synaptic Proteome Changes in the rat Cerebral Cortex

“…In the present study, we identified (with at least 3 peptides) 23 proteins with significantly increased (Table 1) and 23 proteins with decreased ( Table 2) (1) - (Chihara et al, 2007), (2) - (Folci et al, 2014), (3) - (Chen et al, 2002), (4) - (Tanaka et al, 2000), (5) - (Ding and Shen, 2008), (6) - (Na et al, 2012), (7) - (Lyon et al, 2007), (8) - (Sweatt et al, 2004), (9) - (Bahn et al, 2002), (10) - (Manya et al, 1998), (11) - (Kamada et al, 2003), (12) - (McKenna et al, 2000), (13) - (Christel et al, 2012), (GO) -According to Gene Ontology database. …”