WISP-1/CCN4 Potentially Regulates Bone by Controlling Osteogenic Differentiation through BMP-2

Objectives: Wnt-induced Secreted Protein-1 (WISP-1)/CCN4 is expressed in developing bone and is up-regulated during fracture repair. The goal of this study was to determine the role of WISP-1 in controlling bone cell and tissue function and to further determine whether BMP-2 modulation was involved.

Methods: To test the role of WISP-1 in vivo transgenic mice were made to express WISP-1 in bones using the 2.4 KB Col1A1 promoter. The bone mineral density (BMD) of transgenic femurs was first assessed by X-ray and then by a Pixumus DEXA scanner. Adenovirus expressing WISP-1 and BMP-2 were generated and added to human bone marrow stromal cells (hBMSC) separately or in combination. Osteogenic differentiation was assessed using alizarin red accumulation or by qRT-PCR of mRNA for alkaline phosphatase (ALP) or osteopontin (OPN).

Results: X-ray analysis of trangenic mice over-expressing WISP-1 showed that the femurs of female mice were the most affected. DEXA scanning of the same mice showed that the transgenic mice had a small but significant increase in BMD compared to wild-type controls (10% increase; p<0.05). To determine the mechanism causing this increase in BMD the effects of WISP-1 were tested using hBMSC infected with adenovirus to WISP-1 and compared to cells treated with control virus. WISP-1 by itself modestly increased osteogenic differentiation in vitro as judged by alizarin red and ALP and OPN mRNA expression. Interestingly treatment with both WISP-1 with BMP-2 induced significantly higher expression of ALP (12.2 fold; p<0.01) and OPN (2.3 fold; p<0.01) mRNA than with either WISP-1 or BMP-2 alone.

Conclusion: WISP-1 has a positive influence on bone formation and may work by enhancing the effects of BMP-2 to increase osteogenesis.

Supported by the IRP-NIDCR 1 Z01 DE000379-21