ABSTRACT
Osteoarthritis (OA) is the most common chronic disabling joint disease, and currently there is no effective treatment for the cause. Necroptosis plays a key role in many diseases, and receptor-interacting protein kinase 3 (RIP3) is a key regulator during necroptosis process. Studies have shown that the expression level of RIP3 was significantly upregulated in human and mouse OA degenerative cartilage tissues, suggesting the occurrence of necroptosis. However, the specific pathophysiological role of RIP3 in cartilage is still unclear. This study intends to sequence and analyze the transcriptome of chondrocytes before and after RIP3 overexpression, and explore the specific functional mechanism of RIP3 in OA pathogenesis. RNA sequencing results showed that overexpression of RIP3 induced upregulation of 244 genes and downregulation of 277 genes in chondrocytes. Sixteen candidate target genes were screened out by constructing gene co-expression network for further verification at mRNA level, and the results suggested that RIP3 had the most significant inductive effect on the expression of phosphoinositide-3kinase, regulatory subunit 5 (Pik3r5), integrin subunit beta 3 (Itgb3) and MYB proto-oncogene like 2 (Mybl2). Results from CCK-8 and lactate dehydrogenase activity analysis showed that silencing the expression of Itgb3 by siRNA significantly rescued chondrocyte viability decline and necroptosis induced by RIP3, and it also inhibited the upregulating effect of RIP3 on the expression of catabolism-related genes Mmp1, Mmp13 and Il6, as well as the downregulating effect of RIP3 on the expression of anabolism-related genes Acan, Col2a1 and Sox9. This study has demonstrated that RIP3 promotes chondrocyte necrosis and cartilage matrix metabolism disorders by upregulating the expression of Itgb3 in chondrocytes, and ultimately leads to cartilage degeneration. These findings provided potential novel targets for the clinical treatment of OA, and further clarified the pathophysiological significance of necroptosis.
ABSTRACT
<p><b>BACKGROUND</b>The proliferation and apoptosis property of mesenchymal stem cells derived from peripheral blood (PB-MSCs) were investigated under hypoxia and serum deprivation conditions in vitro so as to evaluate the feasibility for autologous PB-MSCs applications in cartilage repair.</p><p><b>METHODS</b>MSCs were mobilized into peripheral blood by granulocyte colony stimulating factor (G-CSF) and AMD3100. The blood samples were collected from central ear artery of rabbits. Adhered cells were obtained by erythrocyte lysis buffer and identified as MSCs by adherence to plastic, spindle shaped morphology, specific surface markers, differentiation abilities into osteoblasts, adipocytes and chondroblasts in vitro under appropriate conditions. MSCs were cultured in four groups at different oxygen tension (20% O2 and 2% O2), with or without 10% fetal bovine serum (FBS) conditions: 20% O2 and 10% FBS complete medium (normal medium, N), 20% O2 and serum deprivation medium (D), 2% O2 and 10% FBS complete medium (hypoxia, H), 2% O2 and serum deprivation (HD). Cell proliferation was determined by CCK-8 assay. Apoptosis was detected by Annexin V/PI and terminal deoxynucleotide transferase dUTP nick end labeling (TUNEL) staining.</p><p><b>RESULTS</b>Spindle-shaped adherent cells were effectively mobilized from peripheral blood by a combined administration of G-CSF plus AMD3100. These cells showed typical fibroblast-like phenotype similar to MSCs from bone marrow (BM-MSCs), and expressed a high level of typical MSCs markers CD29 and CD44, but lacked in the expression of hematopoietic markers CD45 and major histocompatibility complex Class II (MHC II). They could also differentiate into osteoblasts, adipocytes and chondroblasts in vitro under appropriate conditions. No significant morphological differences were found among the four groups. It was found that hypoxia could enhance proliferation of PB-MSCs regardless of serum concentration, but serum deprivation inhibited proliferation at the later stage of culture. Apart from that, hypoxia or serum deprivation could promote the apoptosis of PB-MSCs after 48 hours; the effect was stronger when these two conditions combined together. Furthermore, the effect of serum deprivation on apoptosis was stronger compared with that of hypoxia.</p><p><b>CONCLUSIONS</b>PB-MSCs possess similar phenotypes as BM-MSCs. Their differentiation and proliferation abilities make them a new source of seed cells for ischemia-related cell therapy and tissue engineering in the field of the articular cartilage repair.</p>