LRP4 and Agrin Are Modulated by Cartilage Degeneration and Involved in β-Catenin Signaling in Human Articular Chondrocytes.
This study indicates that intense mechanical strain increases Agrin expression, which may disrupt LRP4's role in cartilage health, but further research is needed to understand the clinical implications.
Where it sits
this study against the rest of the igf-1 lr3 (long r3 igf-1) corpusSummary and findings
This study examined the roles of LRP4 and Agrin in cartilage degeneration using human articular chondrocytes. It was found that LRP4 expression decreased with cartilage degeneration while Agrin expression increased. The study utilized recombinant human Agrin to assess its effects on various gene expressions related to cartilage health.
Abstract
We investigated the roles of low-density lipoprotein receptor-related protein (LRP) 4 and its ligand Agrin in the pathophysiology of cartilage degeneration. Immunohistochemical analysis of human normal articular cartilage and cartilage tissues from patients with osteoarthritis (OA) obtained during surgery of the knee joint showed marked LRP4 expression in the early stages of OA, which then decreased with cartilage degeneration, whereas Agrin was consistently increased with cartilage degeneration. In normal human articular chondrocytes (NHACs), mild cyclic tensile strain (CTS) (0.5 Hz, 5% elongation, 2 h) increased the expression of LRP4 and aggrecan (ACAN), while intense CTS (0.5 Hz, 10% elongation, 6 h) increased the expression of Agrin without affecting LRP4 expression. Treatment with recombinant human (rh) Agrin downregulated the mRNA expression of LRP4 and ACAN, but upregulated the expression of LRP5/6, SRY-box transcription factor 9 (SOX9), Runt-related transcription factor 2 (RUNX2), and a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4). Immunocytochemistry and Western blot analysis showed that rhAgrin treatment upregulated the expression of β-catenin and SOX9. Agrin knockdown by si<i>AGRN</i> transfection partially reduced the nuclear protein expression of β-catenin, which was increased with intense CTS. LRP4 knockdown by si<i>LRP4</i> transfection increased the expression of LRP5/6, SOX9, RUNX2, ADAMTS-4, and Agrin. These results suggested that intense CTS increases the expression of Agrin, which might interfere with the role of LRP4 in the inhibition of LRP5/6 and their downstream β-catenin signaling, leading to cartilage degeneration.
Background
The paper addresses the role of LRP4 and Agrin in the context of cartilage degeneration, which is a significant concern in joint health. Prior research has established that β-Catenin signaling is involved in chondrocyte function and cartilage integrity. Understanding the modulation of these proteins could provide insights into the mechanisms underlying cartilage degeneration.
Methods
Not reported in abstract.
Results
Not reported in abstract.
Interpretation
Not reported in abstract.
Key findings
- Not reported in abstract.
Limitations
- Not reported in abstract.