Activation of the Mammalian Target of Rapamycin Pathway in Endothelial Cells in Antiphospholipid Antibody-Positive Patients with Leg Ulcers

Antiphospholipid antibody (aPL)-induced activation of the mTOR (mammalian target of rapamycin) signaling pathway in endothelial cells plays a role in the pathogenesis of vascular lesions in antiphospholipid syndrome (APS). However, there are no data on whether this mechanism also contributes to the development of skin ulcers commonly observed in APS. We investigated the activation of mTOR in skin specimens from aPL-positive and aPL-negative patients with leg ulcers. Patients with leg ulcers who had primary or secondary APS or no detectable aPLs were included in the study. Biopsies were taken from the ulcer edges and the adjacent non-ulcerated skin areas. Activation of mTORC1 (mTOR Complex1) and mTORC2 (mTOR Complex2) in endothelial cells was determined by immunohistochemical analysis of phosphorylated ribosomal S6 protein (pS6RP) and phosphorylated protein kinase B (pAKT), respectively. In all aPL-positive patients, regardless of whether they had primary or secondary APS, we found a positive immunohistochemical reaction to pS6RP (mTORC1 activation) in the endothelial cells of the ulcer samples. On the other hand, pS6RP could not be detected in samples from aPL-negative chronic venous ulcers. Furthermore, pS6RP was not present in samples taken from the unaffected skin adjacent to the ulcers in aPL-positive patients. The pAKT reaction (mTORC2) was negative in both aPL-positive and aPL-negative patients, both in the ulcers and in the periulcer skin. Activation of the mTOR pathway may contribute to ulcer development in APS. The mTORC1 may be a target for therapeutic modification in APS-associated skin ulcers.