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Angiotensin II and Amyloid-β Synergistically Induce Brain Vascular Smooth Muscle Cell Senescence.

BACKGROUND
Amyloid-β (Aβ) induces cerebrovascular damage and is reported to stimulate endothelial cell senescence. We previously demonstrated that angiotensin II (Ang II) promoted vascular senescence. We examined the possible cross-talk between Ang II and Aβ in regulating brain vascular smooth muscle cell (BVSMC) senescence.


METHODS
BVSMC were prepared from adult male mice and stimulated with Ang II (0, 0.1, 1, 10, 100 nmol/L) and/or Aβ 1-40 (0, 0.1, 0.3, 0.5, 1, 3, 5 µmol/L) for the indicated times. Cellular senescence was evaluated by senescence-associated β-galactosidase staining.


RESULTS
Treatment with Ang II (100 nmol/L) or Aβ (1 µmol/L) at a higher dose increased senescent cells compared with control at 6 days. Treatment with Ang II (10 nmol/L) or Aβ (0.5 µmol/L) at a lower dose had no effect on senescence whereas a combined treatment with lower doses of Ang II and Aβ significantly enhanced senescent cells. This senescence enhanced by lower dose combination was markedly blocked by valsartan (Ang II type 1 receptor inhibitor) or TAK-242 (Aβ receptor TLR4 inhibitor) treatment. Moreover, lower dose combination caused increases in superoxide anion levels and p-ERK expression for 2 days, NF-κB activity, p-IκB, p-IKKα/β, p16 and p53 expression for 4 days, and an obvious decrease in pRb expression. These changes by lower dose combination, except in p-IκB expression and NF-κB activity, were significantly inhibited by pretreatment with U0126 (ERK inhibitor).


CONCLUSIONS
Ang II and Aβ synergistically promoted BVSMC senescence at least due to enhancement of the p-ERK-p16-pRb signaling pathway, oxidative stress and NF-κB/IκB activity.