Effect of lysophosphatidylcholine on renal hemodynamics and excretory function in anesthetized rats

Decreased MARCKS Protein Expression in Kidney Cortex Membrane Fractions of Cathepsin B Knockout Mice Is Associated with Reduced Lysophosphatidylcholine and Protein Kinase C Activity

Cathpesin B is a multi-functional protease that plays numerous roles in physiology and pathophysiology. We hypothesized that actin cytoskeleton proteins that are substrates of cathepsin B, various lipids, and kinases that are regulated by lipids would be down-regulated in the kidney of cathepsin B knockout mice. Here, we show by Western blot and densitometric analysis that the expression and proteolysis of the actin cytoskeleton proteins myristoylated alanine-rich C-kinase substrate (MARCKS) and spectrin are significantly reduced in kidney cortex membrane fractions of cathepsin B knockout mice compared to C57B6 wild-type control mice. Lipidomic results show that specific lipids are increased while other lipids, including lysophosphatidylcholine (LPC) species LPC (16:0), LPC (18:0), LPC (18:1), and LPC (18:2), are significantly decreased in membrane fractions of the kidney cortex from Cathepsin B null mice. Protein Kinase C (PKC) activity is significantly lower in the kidney cortex of cathepsin B knockout mice compared to wild-type mice, while calcium/calmodulin-dependent protein kinase II (CaMKII) activity and phospholipase D (PLD) activity are comparable between the two groups. Together, these results provide the first evidence of altered actin cytoskeleton organization, membrane lipid composition, and PKC activity in the kidneys of mice lacking cathepsin B.

Impaired clearance of apoptotic cells promotes synergy between atherogenesis and autoimmune disease

To clarify the link between autoimmune disease and hypercholesterolemia, we created the gld.apoE^−/− mouse as a model of accelerated atherosclerosis. Atherosclerotic lesion area was significantly increased in gld.apoE^−/− mice compared with apoE^−/− mice. gld.apoE^−/− mice also displayed increases in lymphadenopathy, splenomegaly, and autoantibodies compared with gld mice, and these effects were exacerbated by high cholesterol diet. gld.apoE^−/− mice exhibited higher levels of apoptotic cells, yet a reduced frequency of engulfed apoptotic nuclei within macrophages. Infusion of lysophosphatidylcholine, a component of oxidized low density lipoprotein, markedly decreased apoptotic cell clearance in gld mice, indicating that hypercholesterolemia promotes autoimmune disease in this background. These data suggest that defects in apoptotic cell clearance promote synergy between atherosclerotic and autoimmune diseases.

Lysophosphatidylcholine, a component of stromal phospholipids, as a candidate vasoconstrictive factor in stroma-free hemoglobin

Stroma-free hemoglobin (SFH) contains a trace amount of phospholipids, which has been implicated in the toxic reactions associated with SFH. We analyzed stromal phospholipids by high-performance liquid chromatography and found that SFH contained small quantities of lysophosphatidylcholine (LPC), which is known to be capable of producing a defect in endothelium-dependent arterial relaxation, in addition to major classes of constituent phospholipids in red cell membrane. LPC content was determined to be 1.65 nmol/ml (hemoglobin 8.1 g/dl). To evaluate the role of these stromal phospholipids in SFH-induced vasoconstriction, we next examined the effect of lipids on vascular tone in rabbit aortic strips. Preincubation with the crude lipid extract or the LPC purified from SFH significantly inhibited acetylcholine-induced relaxation in phenylephrine-precontracted tissues. The LPC-induced inhibition was reversed by incubation of the tissues in the absence of lipids, indicating the functional integrity of endothelium. From these results, we propose a possibility that LPC, a component of stromal phospholipids, is a candidate for vasoconstrictive factors present in SFH.