Inherited human cPLA2α deficiency is associated with impaired eicosanoid biosynthesis, small intestinal ulceration, and platelet dysfunction
David H. Adler, Joy D. Cogan, John A. Phillips III, Nathalie Schnetz-Boutaud, Ginger L. Milne, Tina Iverson, Jeffrey A. Stein, David A. Brenner, Jason D. Morrow, Olivier Boutaud, John A. Oates
David H. Adler, Joy D. Cogan, John A. Phillips III, Nathalie Schnetz-Boutaud, Ginger L. Milne, Tina Iverson, Jeffrey A. Stein, David A. Brenner, Jason D. Morrow, Olivier Boutaud, John A. Oates
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Research Article Genetics

Inherited human cPLA2α deficiency is associated with impaired eicosanoid biosynthesis, small intestinal ulceration, and platelet dysfunction

Abstract

Cytosolic phospholipase A2α (cPLA2α) hydrolyzes arachidonic acid from cellular membrane phospholipids, thereby providing enzymatic substrates for the synthesis of eicosanoids, such as prostaglandins and leukotrienes. Considerable understanding of cPLA2α function has been derived from investigations of the enzyme and from cPLA2α-null mice, but knowledge of discrete roles for this enzyme in humans is limited. We investigated a patient hypothesized to have an inherited prostanoid biosynthesis deficiency due to his multiple, complicated small intestinal ulcers despite no use of cyclooxygenase inhibitors. Levels of thromboxane B2 and 12-hydroxyeicosatetraenoic acid produced by platelets and leukotriene B4 released from calcium ionophore–activated blood were markedly reduced, indicating defective enzymatic release of the arachidonic acid substrate for the corresponding cyclooxygenase and lipoxygenases. Platelet aggregation and degranulation induced by adenosine diphosphate or collagen were diminished but were normal in response to arachidonic acid. Two heterozygous single base pair mutations and a known SNP were found in the coding regions of the patient’s cPLA2α genes (p.[Ser111Pro]+[Arg485His; Lys651Arg]). The total PLA2 activity in sonicated platelets was diminished, and the urinary metabolites of prostacyclin, prostaglandin E2, prostaglandin D2, and thromboxane A2 were also reduced. These findings characterize what we believe is a novel inherited deficiency of cPLA2.

Authors

David H. Adler, Joy D. Cogan, John A. Phillips III, Nathalie Schnetz-Boutaud, Ginger L. Milne, Tina Iverson, Jeffrey A. Stein, David A. Brenner, Jason D. Morrow, Olivier Boutaud, John A. Oates

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Figure 8

cPLA2α tertiary structure and location of amino acid substitutions.

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cPLA2α tertiary structure and location of amino acid substitutions. ...
The cPLA2α structure is depicted as a ribbon diagram with α-helices in red, β-strands as blue arrows, loops in gray, and Ca2+ ions as yellow spheres (center). The locations of described amino acid side-chain substitutions are highlighted in green. Three magnified views highlight each mutation. In the left panel, the Ca2+ binding domain is highlighted and shows the S111 position. The upper panel shows that the catalytic domain contains an active site composed of the catalytic dyad of Ser228 and Asp549. Arg200 is also required for catalytic activity (functionally obligate amino acids are shown with yellow carbon atoms and bonds) (11). Arg485 is in proximity to a cluster of lysine residues (blue) that are essential for interfacial binding of cPLA2α (12) and for binding PIP2 (13). p.[R485] is located in a cleft in a helical region containing several positively charged residues in the membrane-facing region of the catalytic domain (11), where the side-chain guanido group forms 2 stabilizing hydrogen-bonding interactions within this fold. A “hinged lid,” which prevents exposure of the active site to substrate until interaction with a lipid membrane is shown in purple. The right panel depicts the location of Lys651, the relative position of which has not been determined.