Tylophorine reduces protein biosynthesis and rapidly decreases cyclin D1, inhibiting vascular smooth muscle cell proliferation in vitro and in organ culture

Abstract

Background
Tylophorine (TYL) is an alkaloid with antiproliferative action in cancer cells. Vascular smooth muscle cell (VSMC) proliferation and neointima formation contribute to restenosis after percutaneous coronary interventions.

Hypothesis/Purpose
Our goal was to examine the potential of TYL to inhibit VSMC proliferation and migration, and to dissect underlying signaling pathways.

Study design and methods
TYL was administered to platelet-derived growth factor (PDGF-BB)-stimulated, serum-stimulated, quiescent and unsynchronized VSMC of rat and human origin. BrdU incorporation and resazurin conversion were used to assess cell proliferation. Cell cycle progression was analyzed by flow cytometry of propidium iodide-stained nuclei. Expression profiles of proteins and mRNAs were determined using western blot analysis and RT-qPCR. The Click-iT OPP Alexa Fluor 488 assay was used to monitor protein biosynthesis.

Results
TYL inhibited PDGF-BB-induced proliferation of rat aortic VSMCs by arresting cells in G1 phase of the cell cycle with an IC50 of 0.13 µmol/l. The lack of retinoblastoma protein phosphorylation and cyclin D1 downregulation corroborated a G1 arrest. Inhibition of proliferation and cyclin D1 downregulation were species- and stimulus-independent. TYL also decreased levels of p21 and p27 proteins, although at later time points than observed for cyclin D1. Co-treatment of VSMC with TYL and MG132 or cycloheximide (CHX) excluded proteasome activation by TYL as the mechanism of action. Comparable time-dependent downregulation of cyclin D1, p21 and p27 in TYL- or CHX-treated cells, together with decreased protein synthesis observed in the Click-iT assay, suggests that TYL is a protein synthesis inhibitor. Besides proliferation, TYL also suppressed migration of PDGF-activated VSMC. In a human saphenous vein organ culture model for graft disease, TYL potently inhibited intimal hyperplasia.

Conclusion
This unique activity profile renders TYL an interesting lead for the treatment of vasculo-proliferative disorders, such as restenosis.


Full text of the study can be accessed at the website of the publisher (journal subscription is needed), can be obtained by one-click-request on ResearchGate (by hitting the “Request full text” button), or can be supplied on demand by email request to [email protected]


Reference:

Joa H, Blažević T, Grojer C, Zeller I, Heiss EH, Atanasov AG, Feldler I, Gruzdaitis P, Czaloun C, Proksch P, Messner B, Bernhard D, Dirsch VM. Tylophorine reduces protein biosynthesis and rapidly decreases cyclin D1, inhibiting vascular smooth muscle cell proliferation in vitro and in organ culture. Phytomedicine. 2019 Apr 23:152938. doi: 10.1016/j.phymed.2019.152938. PubMed PMID: 31078367.



Keywords: Cyclin D1; proliferation; tylophorine; vascular smooth muscle cells; platelet-derived growth factor (PDGF-BB); migration; neointima formation; restenosis after percutaneous coronary interventions; intimal hyperplasia.

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