n‐3 PUFA Alter caveolae lipid composition and resident protein localization in mouse colon

Abstract

Caveolae, by virtue of their unique lipid environment, serve as signaling platforms that regulate cellular events. Perturbations in caveolae lipid composition have been shown in vitro to displace proteins from lipid microdomains, thereby altering their functionality and subsequent downstream signaling. Because membrane remodeling may not be accurately represented by using pharmacological treatments and in vitro models, we investigated the in vivo ability of dietary n-3 polyunsaturated fatty acids (PUFA) to alter caveolae lipid environment and the compartmentalization of resident proteins in mouse colonic mucosa. n-3 PUFA were examined for their chemoprotective, membrane lipid-modifying properties. Colonic caveolae in mice fed n-6 or n-3 PUFA enriched diets were characteristically enriched in cholesterol, sphingomyelin, and caveolin-1. n-3 PUFA feeding, compared with n-6 PUFA, significantly altered colonic caveolae microenvironment by increasing phospholipid n-3 fatty acyl content and reducing both cholesterol (by 46%) and caveolin-1 (by 53%), without altering total cellular levels. Concomitantly, localization of caveolae-resident signaling proteins H-Ras and eNOS in colonic caveolae was decreased by n-3 PUFA, by 45 and 56%, respectively. The distribution of non-caveolae proteins K-Ras and clathrin was unaffected. Moreover, EGF-stimulated H-Ras, but not K-Ras activation was significantly suppressed following n-3 PUFA feeding, in parallel with the selective alterations in their microlocalization. These findings reveal a novel modality by which n-3 PUFA remodel membrane microdomains in vivo and thereby alter caveolae protein localization and functionality.

Activity of BKCa Channel Is Modulated by Membrane Cholesterol Content and Association with Na+/K+-ATPase in Human Melanoma IGR39 Cells

“…It was proposed that phospholipid unsaturation affects membrane thickness and/or lateral organization thereby modulating the activity of Na ϩ /K ϩ -ATPase. Such a modulation could operate in vivo as well because a diet rich in n-3 polyunsaturated fatty acids has been shown to reduce the cholesterol content of colon epithelial membranes by 46% in mice (59). Possible alterations in BK Ca channel activity in these conditions remain to be studied.…”

SCP-2/SCP-x gene ablation alters lipid raft domains in primary cultured mouse hepatocytes

“…Thus, the amount of lipid raft and, thereby, the amount of liquid-ordered phase in hepatocyte plasma membranes, rather than the degree of rigidity of the lipid raft lipids therein, determined the level of ABCA1, SR-B1, and P-gp per milligram of protein in lipid rafts. In contrast, fluidizing lipid rafts by the incorporation of polyunsaturated fatty acids significantly reduces the distribution of caveolin-1 and other proteins into lipid rafts (72,79). iii) SCP-2/SCP-x gene ablation increased the rigidity (decreased fluidity) in hepatocyte lipid rafts, primarily as a result of the increased content of SM and saturated and monounsaturated acyl chains, consistent with SCP-2's ability to selectively bind/transfer other sphingolipids more effectively than SM (see above).…”

“…Although the effect of increased lipid raft rigidity (decreased fluidity) on HDL-mediated cholesterol uptake/efflux in hepatocytes remains to be determined, SCP-2/SCP-x gene ablation reduced hepatic cholesterol and cholesteryl ester content (65), whereas SCP-2 overexpression enhanced hepatic cholesterol accumulation (64). In contrast, incorporation of polyunsaturated fatty acids displaces cholesterol from rafts (80), fluidizes lipid rafts (72,79), increases ABCA1 degradation (81), and reduces RCT (82). iv) SCP-2/SCP-x gene ablation abolished the transbilayer fluidity gradient in lipid rafts of hepatocytes, reflective of the increased exofacial leaflet rigidity (DPH-TMA) concomitant with decreased cytofacial leaflet rigidity (DPH-Pro).…”

Effect of the administration of n-3 polyunsaturated fatty acids on circulating levels of microparticles in patients with a previous myocardial infarction

“…27 For this reason, it is likely that the incorporation of n-3 fatty acids in these cell types modifies membrane properties, such as stability and fluidity, 28 as well as cytosolic calcium concentration, protein localization and functionality in caveolae, 29 reducing cell activation and/or apoptosis, with this translating into lower MP release. Differences in the ability of various cell types to incorporate fatty acids or in their ability to respond functionally to such changes may explain the different cellular responses observed in terms of MP release.…”