Elevated homocysteine levels and apoptosis. Elevated levels of homocysteine directly (branch 1 and 2) or via ER stress (branch 3 and 4) lead to apoptosis. Homocysteine also might lead to cell survival via calcium dependent ERK phosphorylation (branch 5). The genes marked in blue have been identified by literature based searches as mentioned in the methods section. The solid and dotted lines indicate direct and indirect (multi step) interaction/ conversion respectively.