Short-term magnesium deficiency downregulates telomerase, upregulates neutral sphingomyelinase and induces oxidative DNA damage in cardiovascular tissues: relevance to atherogenesis, cardiovascular diseases and aging

Abstract

1) short-term dietary deficiency of magnesium (Mg; 21 days) in rats (MgD) would result in a downregulation of telomerase in cardiac and aortic smooth muscle cells, 2) low levels of Mg(2+) added to drinking water (DW) would either prevent or greatly reduce the downregulation of telomerase in MgD, 3) MgD in rats would cause an upregulation of neutral-sphingomyelinase (N-SMAse) and p53, 4) short-term MgD would result in oxidation of DNA in diverse cardiac muscle and aortic smooth muscle cells as exemplified by measurement of 8-hydroxydeoxyguanosine (8-OH-dG), and 5) cross-talk between telomerase, N-SMase, p53, and 8-OH-dG would be evident in left ventricular (LV), right ventricular (RV), atrial and aortic smooth muscle obtained from rats subjected to short-term MgD. The data indicated that short-term MgD (10% normal dietary intake) resulted in downregulation of telomerase in LV, RV, atrial and aortic muscle cells; even very low levels of water-bourne Mg(2+) (e.g., 15-40 mg/lday) either prevented or ameliorated the downregulation of telomerase. Our experiments also showed that MgD resulted in a 7-10 fold increased formation of 8-OH-dG in the cardiac and aortic muscle cells. The experiments also confirmed that short-term dietary deficiency of Mg resulted in greatly increased upregulation of N-SMAse and p53 in the cardiac and aortic muscle tissues. These new experiments point to a sizeable cross-talk among telomerase, N-SMAse, and p53 in rat cardiac and peripheral vascular muscle exposed to a short-term MgD. These studies would be compatible with the idea that even short-term MgD could cause alterations of the genome in diverse cell types leading to mutations of cardiac, vascular, and endothelial cells seen in aging and atherogenesis. Since we have shown, previously, that activation of N-SMAse in MgD leads to synthesis and release of ceramide in cardiovascular tissues and cells, we believe this pathway, most likely, helps to result in downregulation of telomerase, upregulation of transcription factors (e.g., p53; NF-kB), cytokine release, mutations, transformations, and dysfunctional growth seen in the cardiac and vascular cells observed in the normal aging process, atherogenesis, hypertension, and cardiac failure. Lastly, we suggest ways in which this hypothesis can be tested.

Keywords: 8-hydroxydeoxyguanosine; Cardiac muscle; ceramide; epigenetics; p53; sphingolipids; telomeres; vascular muscle.

Figure 1

Telomerase levels in cardiovascular tissues in normal and MgD rats with and without Mg²⁺ added to the drinking water (DW). All values are Means ± SE. N=14-16 animals per group. All mean values are significantly different from controls, except MgD + 100 mg Mg²⁺/l (P<0.01, ANOVA).

Figure 2

Serum telomerase levels in normal and MgD rats with and without Mg²⁺ added to the DW. All values are Means ± SE. N=14-16 animals per group. All mean values are significantly different from controls, except MgD + 100 mg Mg²⁺/l (P<0.01, ANOVA).

Figure 3

Correlation of cardiovascular tissue levels of telomerase with serum ionized levels of Mg. Regression equations with r-values are as follows: 1) left ventricle (LV) vs. Mg²⁺: y=99.514x-23.296; r=0.9784; 2) right ventricle (RV) vs. Mg²⁺: y=76.663x-4.565; r=0.848; 3) atria vs. Mg²⁺: y=74.566x-10.939; r=0.9165; and 4) aorta vs. Mg²⁺: y=98.784x-19.813; r=0.9866.

Figure 4

N-SMAse levels in LV, RV, atria and aortic smooth muscle in normal and MgD rats. All values are Means ± SE. N=14-16 animals per group. All MgD mean values are significantly different from control rats (P<0.01, ANOVA).

Figure 5

Inverse correlations of telomerase levels with N-SMASes in cardiovascular tissues.

Figure 6

p53 levels in cardiovascular tissues in normal and MgD rats. All values are Means ± SE. All MgD mean values are significantly different from controls (P<0.001, ANOVA).

Figure 7

Inverse correlations of telomerase levels with p53 in cardiovascular tissues. Regression equations with r-values are as follows: 1) left ventricle vs. p53: y=-16-719x+989.29; r=0.9371; 2) right ventricle vs. p53: y=-18.619x+1194.6; r=0.676; 3) atria vs. p53: y=-22.63x+959.68; r=0.9915; and 4) aortic smooth muscle vs. p53: y=-1.205x+1051.3; r=0.9406.

Figure 8

Multiple regression analysis of and N-SMAses and p53 with telomerase in cardiovascular tissues from normal and MgD rats with and without Mg²⁺ added to the DW.

Figure 9

8-OHdG levels in cardiovascular tissues of MgD and control rats with and without Mg²⁺ added to the drinking water. N=14-16 animals per group. All values are Means ± SE. All mean values are significantly different from controls (P<0.01).