Myeloid- and hepatocyte-specific deletion of group VIA calcium-independent phospholipase A2 leads to dichotomous opposing phenotypes during MCD diet-induced NASH

Polymorphisms of phospholipase A2VIA (iPLA2β or PLA2G6) are associated with body weights and blood C-reactive protein. The role of iPLA2β/PLA2G6 in non-alcoholic steatohepatitis (NASH) is still elusive because female iPla2β-null mice showed attenuated hepatic steatosis but exacerbated hepatic fibrosis after feeding with methionine- and choline-deficient diet (MCDD). Herein, female mice with myeloid- (MPla2g6^-/-) and hepatocyte- (LPla2g6^-/-) specific PLA2G6 deletion were generated and phenotyped after MCDD feeding. Without any effects on hepatic steatosis, MCDD-fed MPla2g6^-/- mice showed further exaggeration of liver inflammation and fibrosis as well as elevation of plasma TNFα, CCL2, and circulating monocytes. Bone-marrow-derived macrophages (BMDMs) from MPla2g6^-/- mice displayed upregulation of PPARγ and CEBPα proteins, and elevated release of IL6 and CXCL1 under LPS stimulation. LPS-stimulated BMDMs from MCDD-fed MPla2g6^-/- mice showed suppressed expression of M1 Tnfa and Il6, but marked upregulation of M2 Arg1, Chil3, IL10, and IL13 as well as chemokine receptors Ccr2 and Ccr5. This in vitro shift was associated with exaggeration of hepatic M1/M2 cytokines, chemokines/chemokine receptors, and fibrosis genes. Contrarily, MCDD-fed LPla2g6^-/- mice showed a complete protection which was associated with upregulation of Ppara/PPARα and attenuated expression of Pparg/PPARγ, fatty-acid uptake, triglyceride synthesis, and de novo lipogenesis genes. Interestingly, LPla2g6^-/- mice fed with chow or MCDD displayed an attenuation of blood monocytes and elevation of anti-inflammatory lipoxin A4 in plasma and liver. Thus, PLA2G6 inactivation specifically in myeloid cells and hepatocytes led to opposing phenotypes in female mice undergoing NASH. Hepatocyte-specific PLA2G6 inhibitors may be further developed for treatment of this disease.

Targeting the annulus fibrosus of the intervertebral disc: Col1a2-Cre(ER)T mice show specific activity of Cre recombinase in the outer annulus fibrosus

Degeneration of the intervertebral disc (IVD) is a major underlying contributor to back pain-the single leading cause of disability worldwide. However, we possess a limited understanding of the etiology underlying IVD degeneration. To date, there are a limited number of mouse models that have been used to target proteins in specific compartments of the IVD to explore their functions in disc development, homeostasis and disease. Furthermore, the majority of reports exploring the composition and function of the outer encapsulating annulus fibrosus (AF) of the IVD have considered it as one tissue, without considering the numerous structural and functional differences existing between the inner and outer AF. In addition, no mouse models have yet been reported that enable specific targeting of genes within the outer AF. In the current report, we discuss these issues and demonstrate the localized activity of Cre recombinase in the IVD of Col1a2-Cre(ER)T;ROSA26mTmG mice possessing a tamoxifen-dependent Cre recombinase driven by a Cola2 promoter and distal enhancer and the mTmG fluorescent reporter. Following tamoxifen injection of 3-week-old Col1a2-Cre(ER)T;ROSA26mTmG mice, we show Cre activity specifically in the outer AF of the IVD, as indicated by expression of the GFP reporter. Thus, Col1a2-Cre(ER)T;ROSA26mTmG mice may prove to be a valuable tool in delineating the function of proteins in this unique compartment of the IVD, and in further exploring the compositional differences between the inner and outer AF in disc homeostasis, aging and disease.