Group VIA iPLA2 (iPLA2b) or PLA2G6 catalyzes hydrolysis of phospholipids at the sn-2
position, releasing a fatty acid and a lysophospholipid which has been shown to mediate
neutrophil adhesion and monocyte migration in immune cells. Moreover, PLA2G6 single
nucleotide polymorphism is associated with serum C-reactive protein suggesting PLA2G6
role in inflammation. Therefore, we aim to investigate whether Pla2G6 deficiency in
macrophages could modulate liver injury by altering differentiation programs of lymphocyte
antigen 6 complex (Ly6C) in the bone marrow.
Methods:
Macrophage-specific (lysMCre) Pla2G6 KO mice with exon 6 – 8 deletion were generated.
Bone marrow-derived macrophages (BMDM) from control and KO mice were prepared. Acute
liver injury was induced by intraperitoneal injection of acetaminophen (APAP 300 mg/kg),
and mice were killed 24h later. Liver injury and gene expression analyses were assessed.
BMDM phospholipids were measured by LC-MS. CD45+CD11b+CD115+Ly6G-Ly6C+ monocytes were
measured by FACS.
Results:
BMDM of KO mice showed the absence of Pla2G6 protein and mRNA. Livers of KO mice still
showed Pla2G6 protein expression indicating specific deletion in macrophages. By LC-MS
analysis, BMDM from KO mice showed a significant decrease in monounsaturated lysophosphatidylcholine
(LPC) and 18:2 LPC, and an increase of phosphatidylinositol (PI) 40:5 and phosphatidylserine
(PS) 40:5. Upon APAP treatment, male KO mice showed a significant increase of AST,
and a trend increase of ALT, LDH, and caspase3 activity. BMDM and livers of male KO
mice respectively showed increased IL-6 mRNA and protein expression. The analyses
of Ly6C mRNA expression and % ly6C+ monocytes by FACS showed no difference between
male control and KO. On the other hand, female KO mice showed no worsening liver injury.
However BMDM of female mutants showed a significant increase of ly6C mRNA expression,
a trend increase of the M2 markers, Retnla and Chi3l3. Consistently, FACS results
of BMDM showed a significant increase of % ly6C+ monocytes in these female KO mice.
Conclusions:
Pla2G6 has specificity in the hydrolysis of PI and PS in BMDM. Male KO BMDM showed
no alteration of ly6C while female KO BMDM showed an increase of ly6C. As ly6C is
thought to be involved in inflammation and resolution and that male KO mice showing
worsen liver injury than female KO mice, hence deficiency of Pla2G6 in macrophages
may modulate acute liver injury in a ly6C- and sex-dependent manner.
