MDL-72527

The aging of the global population has necessitated the identification of effective anti-aging technologies based on scientific evidence. Polyamines (putrescine, spermidine, and spermine) are essential for cell growth and function. Age-related reductions in polyamine levels have been shown to be associated with reduced cognitive and physical functions. We have previously found that the expression of spermine oxidase (SMOX) increases with age; however, the relationship between SMOX expression and cellular senescence remains unclear. Therefore, we investigated the relationship between increased SMOX expression and cellular senescence using human-liver-derived HepG2 cells. Intracellular spermine levels decreased and spermidine levels increased with the serial passaging of cells (aged cells), and aged cells showed increased expression of SMOX. The levels of acrolein-conjugated protein, which is produced during spermine degradation, also increases. Senescence-associated β-gal activity was increased in aged cells, and the increase was suppressed by MDL72527, an inhibitor of acetylpolyamine oxidase (AcPAO) and SMOX, both of which are enzymes that catalyze polyamine degradation. DNA damage accumulated in aged cells and MDL72527 reduced DNA damage. These results suggest that the SMOX-mediated degradation of spermine plays an important role in cellular senescence. Our results demonstrate that cellular senescence can be controlled by inhibiting spermine degradation using a polyamine-catabolizing enzyme inhibitor.

Acrolein, a highly reactive unsaturated aldehyde, is known to facilitate glial cell migration, one of the pathological hallmarks in diabetic retinopathy. However, cellular mechanisms of acrolein generation in retinal glial cells remains elusive. In the present study, we investigated the role and regulation of spermine oxidase (SMOX), one of the enzymes related to acrolein generation, in retinal glial cells under hypoxic condition.

Immunofluorescence staining for SMOX was performed using sections of fibrovascular tissues obtained from patients with proliferative diabetic retinopathy. Expression levels of polyamine oxidation enzymes including SMOX were analyzed in rat retinal Müller cell line 5 (TR-MUL5) cells under either normoxic or hypoxic conditions. The transcriptional activity of Smox in TR-MUL5 cells was evaluated using the luciferase assay. Levels of acrolein-conjugated protein, Nε-(3-formyl-3,4-dehydropiperidino) lysine adduct (FDP-Lys), and hydrogen peroxide were measured.

SMOX was localized in glial cells in fibrovascular tissues. Hypoxia induced SMOX production in TR-MUL5 cells, which was suppressed by silencing of hypoxia-inducible factor-1α (Hif1a), but not Hif2a. Transcriptional activity of Smox was regulated through HIF-1 binding to hypoxia response elements 2, 3, and 4 sites in the promoter region of Smox. Generation of FDP-Lys and hydrogen peroxide increased in TR-MUL5 cells under hypoxic condition, which was abrogated by SMOX inhibitor MDL72527.

The current data demonstrated that hypoxia regulates production of SMOX, which plays a role in the generation of oxidative stress inducers, through HIF-1α signaling in Müller glial cells under hypoxic condition.