Short-term Mg deficiency upregulates protein kinase C isoforms in cardiovascular tissues and cells; relation to NF-kB, cytokines, ceramide salvage sphingolipid pathway and PKC-zeta: hypothesis and review

Burton M Altura, Nilank C Shah, Gatha J Shah, Aimin Zhang, Wenyan Li, Tao Zheng, Jose Luis Perez-Albela, Bella T Altura, Burton M Altura, Nilank C Shah, Gatha J Shah, Aimin Zhang, Wenyan Li, Tao Zheng, Jose Luis Perez-Albela, Bella T Altura

Abstract

Numerous recent,epidemiological studies reveal that Western populations are growing more and more deficient in daily Mg intake which have been linked to etiology of cardiovascular (CV) diseases. A growing body of evidence suggests that a major missing link to this dilemma may reside within the sphingolipid-ceramide pathways. For the past 25 years , our labs have been focusing on these pathways in Mg-deficient mammals. The objective of this paper is two-fold: 1) to test various hypotheses and 2) to review the current status of the field and how protein kinase C isoforms may be pivotal to solving some of the CV attributes of Mg deficiency. Below, we test the hypotheses that: 1) short-term dietary deficiency of magnesium (MgD) would result in the upregulation of protein kinase C (PKC) isoforms in left ventricular (LV) and aortic smooth muscle (ASM) and serum; 2) MgD would result in a release of select cytokines and an upregulation of NF-kB in LV and ASM, and in primary cultured aortic smooth muscle cells (PCASMC); 3) MgD would result in an activation of the sphingolipid salvage pathway in LV and ASM, and in PCASMC; 4) MgD would result in a synthesis of sphingosine, but not sphinganine, in PCASMC which could be inhibited by fumonisin B1 (FB) an inhibitor of ceramide synthase (CS), but not scyphostatin an inhibitor of neutral sphingomyelinase (N-SMase); 5) incubation of PCASMC (in low Mg(2+)) with the PKC-mimic PMA would result in release and synthesis of NF-kB, cytokines, and ceramide but not sphingosine. The new data indicate that short-term MgD (10% normal dietary intake) result in an upregulation of all three classes of PKC isoforms in LV, aortic muscle and in serum coupled to the upregulation of ceramide, NF-kB activation, and cytokines. High degrees of linear correlation were found to exist between upregulation of PKC isoforms, p65 and cytokine release, suggesting cross-talk between these molecules and molecular pathways. Our experiments with PCASMCs demonstrated that MgD caused a pronounced synthesis of sphingosine (but not sphinganine), which could be inhibited with fumonisin B1, but not by scyphostatin; use of PMA stimulation released ceramide but not sphingosine suggesting a role for the "sphingolipid salvage pathway" in MgD vascular muscle. Use of different PKC pharmacological inhibitors suggested that although all three classes of PKC molecules, i.e., classical, novel, and atypical, play roles in MgD-induced synthesis/release of ceramide, sphingosine, and cytokines as well as activation of NF-kB, to varying degrees, PKC-zeta appears to play a greater role in these events than any of the other PKC isoforms; a specific PKC-zeta inhibitory peptide inhibited formation of sphingosine. Even low levels of water-borne Mg (e.g., 15 mg/l/day) either prevented or ameliorated the upregulation of all three classes of PKC isoforms. An attempt is made to integrate our new data with previous information in order to possibly explain many of the cardiovascular effects of MgD.

Keywords: Cardiac muscle; ceramide synthase; p65; sphingosine; vascular muscle; water-borne magnesium.