A Novel Role for Plasminogen Activator Inhibitor Type-2 as a Hypochlorite-Resistant Serine Protease Inhibitor and Holdase Chaperone

Abstract

Plasminogen activator inhibitor type-2 (PAI-2), a member of the serpin family, is dramatically upregulated during pregnancy and in response to inflammation. Although PAI-2 exists in glycosylated and non-glycosylated forms in vivo, the majority of in vitro studies of PAI-2 have exclusively involved the intracellular non-glycosylated form. This study shows that exposure to inflammation-associated hypochlorite induces the oligomerisation of PAI-2 via a mechanism involving dityrosine formation. Compared to plasminogen activator inhibitor type-1 (PAI-1), both forms of PAI-2 are more resistant to hypochlorite-induced inactivation of its protease inhibitory activity. Holdase-type extracellular chaperone activity plays a putative non-canonical role for PAI-2. Our data demonstrate that glycosylated PAI-2 more efficiently inhibits the aggregation of Alzheimer’s disease and preeclampsia-associated amyloid beta peptide (Aβ), compared to non-glycosylated PAI-2 in vitro. However, hypochlorite-induced modification of non-glycosylated PAI-2 dramatically enhances its holdase activity by promoting the formation of very high-molecular-mass chaperone-active PAI-2 oligomers. Both PAI-2 forms protect against Aβ-induced cytotoxicity in the SH-SY5Y neuroblastoma cell line in vitro. In the villous placenta, PAI-2 is localised primarily to syncytiotrophoblast with wide interpersonal variation in women with preeclampsia and in gestational-age-matched controls. Although intracellular PAI-2 and Aβ staining localised to different placental cell types, some PAI-2 co-localised with Aβ in the extracellular plaque-like aggregated deposits abundant in preeclamptic placenta. Thus, PAI-2 potentially contributes to controlling aberrant fibrinolysis and the accumulation of misfolded proteins in states characterised by oxidative and proteostasis stress, such as in Alzheimer’s disease and preeclampsia.

Preeclampsia and its relationship to pathological brain aging

“…Another potential regulator of misfolded proteins is glycosylated plasminogen activator inhibitor type-2 (PAI-2), which is upregulated in pregnancy and in response to inflammation. Research has shown that glycosylated PAI-2 inhibits the aggregation of β-amyloid peptides and is implicated in cases of preeclampsia and AD ( Cater et al, 2022 ). Anti-aging protein α-klotho also differs in concentration by pregnancy outcome and studies have shown maternal plasma levels of α-klotho were elevated in preeclampsia ( Loichinger et al, 2016 ).…”

Hypochlorous Acid and Chloramines Induce Specific Fragmentation and Cross-Linking of the G1-IGD-G2 Domains of Recombinant Human Aggrecan, and Inhibit ADAMTS1 Activity

“…Some of these cross-links have been identified (on the basis of their loss under reducing conditions) as interchain disulfides (e.g., [74]). Others are nonreducible, including di-tyrosine (e.g., [75]), tryptophan-derived linkages (e.g., [76]) or Schiff-based structures [72]. Sulfenamide, sulfinamide, and sulfonamide links have also been identified [77,78].…”

Protein Misfolding in Pregnancy: Current Insights, Potential Mechanisms, and Implications for the Pathogenesis of Preeclampsia

“…Studies investigating the role of TTR dysregulation and aggregation in driving PEassociated dysfunction also lay out two potential mechanisms contributing to the production and deposition of protein aggregates in the PE placenta: increased ER stress and impaired autophagy [134]. Studies looking into mechanisms of Aβ aggregation highlight a third major mechanism: dysregulation of chaperone proteins [135,136]. Together these studies paint a clear picture of how protein aggregation may come about in PE.…”