A Critical Role for Ceramide Synthase 2 in Liver Homeostasis

Abstract

Ceramide is an important lipid signaling molecule that plays critical roles in regulating cell behavior. Ceramide synthesis is surprisingly complex and is orchestrated by six mammalian ceramide synthases, each of which produces ceramides with restricted acyl chain lengths. We have generated a CerS2 null mouse and characterized the changes in the long chain base and sphingolipid composition of livers from these mice. Ceramide and downstream sphingolipids were devoid of very long (C22-C24) acyl chains, consistent with the substrate specificity of CerS2 toward acyl-CoAs. Unexpectedly, C16-ceramide levels were elevated, and as a result, total ceramide levels were unaltered; however, C16-ceramide synthesis in vitro was not increased. Levels of sphinganine were also significantly elevated, by up to 50-fold, reminiscent of the effect of the ceramide synthase inhibitor, fumonisin B1. With the exceptions of glucosylceramide synthase and neutral sphingomyelinase 2, none of the other enzymes tested in either the sphingolipid biosynthetic or degradative pathways were significantly changed. Total glycerophospholipid and cholesterol levels were unaltered, although there was a marked elevation in C18:1 and C18:2 fatty acids in phosphatidylethanolamine, concomitant with a reduction in C18:0 and C20:4 fatty acids. Finally, differences were observed in the biophysical properties of lipid extracts isolated from liver microsomes, with membranes from CerS2 null mice displaying higher membrane fluidity and showing morphological changes. Together, these results demonstrate novel modes of cross-talk and regulation between the various branches of lipid metabolic pathways upon inhibition of very long acyl chain ceramide synthesis.Biological membranes contain thousands of different lipid species that can be broadly classified according to their backbone structure (1). Of these, sphingolipids (SL) 2 have become particularly prominent due to the discovery of their unexpected structural complexity and their intricate modes of cellular trafficking and metabolism (2-4). Ceramides are perhaps the most well studied class of SLs, because of their essential roles in differentiation and in apoptosis (5-7). Ceramides can differ in both their long chain sphingoid base (8) and fatty acid composition (9). Over the past few years, a complex mode of regulation of ceramide synthesis has been described, with each of the six mammalian ceramide synthase (CerS) (formerly known as Lass (longevity assurance)) genes generating ceramides with specific acyl chain lengths (10). Thus, CerS1 uses mostly C18-CoA (11); CerS4 uses C18-and C20-CoAs (12); CerS5 and CerS6 use mostly C16-CoA (12, 13); and CerS3 uses very long chain acyl-CoAs (C26 and higher) (14). CerS2 can utilize a wider range of fatty acyl-CoAs but uses mainly C22 to C24. In addition, CerS2 displays complex modes of regulation and has genomic features characteristic of a "housekeeping" gene, although no other CerS genes display these characteristics (15).We have now generated a CerS2 null mouse and have ...

Ablation of ceramide synthase 2 exacerbates dextran sodium sulphate‐induced colitis in mice due to increased intestinal permeability

“…Similar to the SL composition in liver reported earlier 23, levels of long‐chain bases, including sphingosine and sphinganine, and C16‐ceramides were significantly elevated with concomitant decrease of C22‐C24 ceramides in the colon of CerS2 null mice (Fig. 2A and B), and total ceramide levels were not different between CerS2 null and WT mice (Fig.…”

“…2A and B), and total ceramide levels were not different between CerS2 null and WT mice (Fig. 2B), which is also similar to the liver 23. However, DSS administration in both WT and CerS2 null mice increased total ceramide levels as well as levels of long chain bases, which suggests activation of the de novo SL synthesis pathway (Fig.…”

“…CerS2‐null mice have been described previously 23, 24. Mice, 6–10 week of age, were housed under special pathogen‐free conditions at 21–23°C and 51–54% humidity with a 12‐hr light–dark cycle and were supplied with food and water ad libitum .…”

Altering sphingolipid composition with aging induces contractile dysfunction of gastric smooth muscle via KCa1.1 upregulation

“…S1, Supporting information). A previous study reported that levels of SP and sphinganine are increased in CerS2‐null mice (Pewzner‐Jung et al ., 2010). These results suggest that aging and CerS2 ablation induce similar change in SL composition.…”

K Ca 3.1 upregulation preserves endothelium‐dependent vasorelaxation during aging and oxidative stress

“…CerS2 null mice were generated as described (Pewzner‐Jung et al ., 2010), and catalase −/− /GPX1 −/− mice were generously donated by Dr. Ye‐Shih Ho (Wayne State Medical School, Detroit, MI) (Johnson et al ., 2010). We studied CerS2 null mice (15‐ or 25‐week‐old; n  = 120) and age‐matched wild‐type (F1 of 129S4/SvJae × C57BL/6) mice ( n  = 85), GPX1 −/− /catalase −/− mice (15‐ or 25‐week‐old; n  = 22) and age‐matched C57BL/6 wild‐type mice ( n  = 18), and aged (75‐ and 100‐week‐old; n  = 25 and 18, respectively) and young (15‐week‐old; n  = 30) C57BL/6 wild‐type mice.…”