Role of Fibulin 3 in Aging-Related Joint Changes and Osteoarthritis Pathogenesis in Human and Mouse Knee Cartilage

The EFEMP1 gene encoding fibulin 3 is specifically expressed in the superficial zone (SZ) of articular cartilage. The aims of this study were to examine the expression patterns of fibulin 3 in the knee joints during aging and during osteoarthritis (OA) and to determine the role of fibulin 3 in the pathogenesis of OA.

Immunohistochemical analysis was performed on normal and OA knee cartilage samples from humans and mice. Experimental OA was induced in wild-type and fibulin 3^-/- mice, and the severity of OA was evaluated by histologic scoring. To examine fibulin 3 function, human chondrocyte monolayer cultures were transfected with small interfering RNA (siRNA), followed by quantitative polymerase chain reaction and Western blot analyses. Human bone marrow-derived mesenchymal stem cells (BM-MSCs) were transduced with an EFEMP1 lentivirus and analyzed for markers of chondrogenesis.

Fibulin 3 was specifically expressed in the SZ of normal knee joint cartilage from humans and mice, and the expression levels declined with aging. Both aging-related OA and experimental OA were significantly more severe in fibulin 3^-/- mice compared with wild-type mice. Fibulin 3 expression was high in undifferentiated human BM-MSCs and decreased during chondrogenesis. Suppression of fibulin 3 by siRNA significantly increased the expression of SOX9, type II collagen, and aggrecan in human articular chondrocytes, while overexpression of fibulin 3 inhibited chondrogenesis in BM-MSCs.

Fibulin 3 is specifically expressed in the SZ of articular cartilage and its expression is reduced in aging and OA. Fibulin 3 regulates differentiation of adult progenitor cells, and its aging-related decline is an early event in the pathogenesis of OA. Preventing aging-associated loss of fibulin 3 or restoring it to normal levels in SZ chondrocytes has the potential to delay or prevent the onset of OA.