Tyre antioxidant 6PPD causes unexplained miscarriage by inducing placental senescence via P21 upregulation

Unexplained miscarriage (UM) significantly impacts human reproduction, with its underlying causes often remaining elusive. Cellular senescence, a state of irreversible cell cycle arrest, is increasingly implicated in various pathologies, including reproductive health issues. Globally, the widespread use and wear of tyres lead to pervasive environmental pollution by 6PPD, an antioxidant found in tyres, with detectable levels even in pregnant women. Despite its prevalence, the critical question of whether 6PPD exposure can induce senescence and contribute to UM has largely been unaddressed, highlighting an urgent need for investigation into this potential environmental health risk.

Researchers conducted a combined case-control study involving a UM group (n=50) and healthy controls, alongside in vitro functional assays using a mouse model and human trophoblast HTR-8/SVneo cells. The study explored associations between environmental 6PPD exposure and cellular senescence. In the mouse model, animals were exposed to 6PPD at doses ≥12 mg/kg/d to assess placental senescence and ≥36 mg/kg/d for miscarriage induction. Key endpoints included urinary 6PPD levels, villous and placental tissue senescence, and the investigation of BAZ1B-mediated ubiquitination degradation of P21 using techniques like qPCR and Western blot to analyze protein expression and ubiquitination status.

Higher urinary 6PPD levels were significantly associated with villous tissue senescence and miscarriage in the human case-control group (n=50). The 6PPD-exposed mouse model further confirmed that exposure to high doses of 6PPD caused placental senescence at ≥12 mg/kg/d and induced mouse miscarriage at ≥36 mg/kg/d. Mechanistically, 6PPD exposure consistently down-regulated BAZ1B expression levels across human villous tissues, mouse placentas, and trophoblast cells. This suppression of BAZ1B subsequently inhibited BAZ1B-mediated ubiquitination degradation of P21, leading to an up-regulation of P21 protein levels. > The up-regulated P21 then triggered cellular senescence, which was identified as a direct cause of miscarriage. Therapeutic interventions, including down-regulation of p21, supplementation with murine Baz1b, or direct suppression of senescence, effectively reduced placental senescence and suppressed mouse miscarriage in the 6PPD-exposed models.