Deficiency of Macf1 in osterix expressing cells decreases bone formation by Bmp2/Smad/Runx2 pathway.

Wu‐Xia Qiu,Fan Zhao,Ru Zhang,Ke‐Wen Zhang,Kai Dang,Ai‐Rong Qian,Xiao‐Li Ma,Pai Wang,Yun‐Yun Xiao,Di‐Jie Li,Xiao Lin,Zhi‐Hao Chen,Xiao‐Yang Wu,Zhi‐Ping Miao

doi:10.1111/jcmm.14729

Abstract

Microtubule actin cross‐linking factor 1 (Macf1) is a spectraplakin family member known to regulate cytoskeletal dynamics, cell migration, neuronal growth and cell signal transduction. We previously demonstrated that knockdown of Macf1 inhibited the differentiation of MC3T3‐E1 cell line. However, whether Macf1 could regulate bone formation in vivo is unclear. To study the function and mechanism of Macf1 in bone formation and osteogenic differentiation, we established osteoblast‐specific Osterix (Osx) promoter‐driven Macf1 conditional knockout mice (Macf1f/fOsx‐Cre). The Macf1f/fOsx‐Cre mice displayed delayed ossification and decreased bone mass. Morphological and mechanical studies showed deteriorated trabecular microarchitecture and impaired biomechanical strength of femur in Macf1f/fOsx‐Cre mice. In addition, the differentiation of primary osteoblasts isolated from calvaria was inhibited in Macf1f/fOsx‐Cre mice. Deficiency of Macf1 in primary osteoblasts inhibited the expression of osteogenic marker genes (Col1, Runx2 and Alp) and the number of mineralized nodules. Furthermore, deficiency of Macf1 attenuated Bmp2/Smad/Runx2 signalling in primary osteoblasts of Macf1f/fOsx‐Cre mice. Together, these results indicated that Macf1 plays a significant role in bone formation and osteoblast differentiation by regulating Bmp2/Smad/Runx2 pathway, suggesting that Macf1 might be a therapeutic target for bone disease.

Highlights

Microtubule actin cross‐linking factor 1 (Macf1), known as Actin cross‐linking factor 7 (Acf7), is a member of spectraplakin family.[1,2] Macf[1] can crosslink with actin and microtubules and plays pivotal roles in cytoskeletal dynamics, cell migration, neu‐ ronal growth and cell signal transduction.[3-6]
The results showed that the mRNA and protein expression of alkaline phosphatase (Alp), Col[1] and Runx[2] were decreased in primary osteoblasts of Macf1f/fOsx‐Cre mice after 7 days induction (Figure 4B,4)
Our data demon‐ strated that deficiency of Macf[1] in osteoblast reduced bone forma‐ tion and osteoblast differentiation by affecting the bone morphogenetic protein 2 (Bmp2)/Smad/ Runx[2] pathway

Summary

| INTRODUCTION

Microtubule actin cross‐linking factor 1 (Macf1), known as Actin cross‐linking factor 7 (Acf7), is a member of spectraplakin family.[1,2] Macf[1] can crosslink with actin and microtubules and plays pivotal roles in cytoskeletal dynamics, cell migration, neu‐ ronal growth and cell signal transduction.[3-6]. It was demonstrated that Macf[1] can regulate the proliferation, cell cycle progression and differentiation of MC3T3‐E1 osteoblastic cell line.[16-19]. It remains unknown whether Macf[1] could reg‐ ulate bone formation in vivo. Runx[2] is a master transcription factor necessary for os‐ teoblast differentiation, which can regulate the expression of osteoblast‐specific genes including alkaline phosphatase (Alp), collagen type I (Col1) and osteocalcin (Ocn).[23]. It has been re‐ ported that Wnt/β‐catenin pathway can regulate the activation of BMP2 transcription in osteoblasts.[5,24]. We provided a new mice model for in vivo function research of Macf[1] and targeted therapy research of osteoporosis

| MATERIALS AND METHODS

Findings

| DISCUSSION