Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA363

Poster Communications

Role of cytosolic serine hydroxymethyl transferase 1 (SHMT1) in osteo-/chondrogenic transdifferentiation and calcification of vascular smooth muscle cells

B. Boehme1, N. Schelski1, M. Makridakis2, A. Vlahou2, F. Lang3, B. Pieske1,4,5, I. Alesutan1,4, J. Voelkl1

1. Center for Cardiovascular Research Cardiology CVK, Charité - Universitätsmedizin Berlin, Berlin, Germany. 2. Biomedical Research Foundation, Academy of Athens, Athens, Greece. 3. Department of Physiology I, Eberhard-Karls University, Tübingen, Germany. 4. Berlin Institute of Health, Berlin, Germany. 5. Department of Internal Medicine and Cardiology, DHZB, Berlin, Germany.

Background: Polymorphisms in the cytosolic serine hydroxymethyl transferase 1 (SHMT1) gene, a key enzyme in one carbon (methyl) metabolism, are associated with increased risk of cardiovascular events. However, the physiological roles of SHMT1 in vascular smooth muscle cell (VSMC) function are still elusive. Medial vascular calcification is a risk factor for cardiovascular events and mortality in chronic kidney disease (CKD) patients. Thus, the aim of the present study was to examine the possible involvement of SHMT1 in phosphate-induced osteo-/chondrogenic transdifferentiation and calcification of VSMCs. Methods: Experiments were performed in primary human aortic smooth muscle cells (HAoSMCs) following silencing of the SHMT1 gene by small interfering RNA and additional treatment with control or high phosphate and/or antioxidants TIRON and TEMPOL. The mRNA expression was determined by qRT-PCR, total antioxidant capacity and tissue-nonspecific alkaline phosphatase (ALPL) activity by colorimetric assays and calcification by quantification of calcium content and Alizarin Red staining. Results: Phosphate treatment up-regulated SHMT1 mRNA expression in HAoSMCs. Silencing of endogenous SHMT1 expression in HAoSMCs significantly increased osteogenic transcription factors MSX2 and CBFA1 mRNA expression as well as ALPL mRNA expression and activity as compared to negative control silenced HAoSMCs, effects suggesting an increased osteo-/chondrogenic transdifferentiation. In addition, calcification analysis revealed higher mineral deposition in SHMT1 siRNA silenced HAoSMCs than in negative control siRNA silenced HAoSMCs. Silencing of SHMT1 decreased total antioxidant capacity and up-regulated superoxide-generating NADH/NADPH oxidase system components NOX4 and CYBA mRNA expression in HAoSMCs and, thus, SHMT1 knockdown induced cellular oxidative stress. In accordance, silencing of SHMT1 promoted oxidative stress-downstream osteogenic signaling, which includes increased mRNA expression of matrix metalloproteinase MMP2 as well as apoptosis marker BAX/BCL2 expression ratio in HAoSMCs. Additional treatment with antioxidants TIRON or TEMPOL was able to blunt the increased osteogenic markers mRNA expression in SHMT1 silenced HAoSMCs. Conclusions: Silencing of SHMT1 promotes osteo-/chondrogenic signaling in VSMCs, at least partly, by inducing cellular oxidative stress and aggravates calcification of VSMCs during high phosphate conditions. The present observations advocate for a regulatory role of SHMT1 in VSMC calcification during pathological conditions such as CKD.

Where applicable, experiments conform with Society ethical requirements