A Conditional Knockout Mouse Model Reveals a Critical Role of PKD1 in Osteoblast Differentiation and Bone Development

Abstract

The protein kinase D family of serine/threonine kinases, particularly PKD1, has been implicated in the regulation of a complex array of fundamental biological processes. However, its function and mechanism underlying PKD1-mediated the bone development and osteoblast differentiation are not fully understood. Here we demonstrate that loss of PKD1 function led to impaired bone development and osteoblast differentiation through STAT3 and p38 MAPK signaling using in vitro and in vivo bone-specific conditional PKD1-knockout (PKD1-KO) mice models. These mice developed markedly craniofacial dysplasia, scapula dysplasia, long bone length shortage and body weight decrease compared with wild-type littermates. Moreover, deletion of PKD1 in vivo reduced trabecular development and activity of osteoblast development, confirmed by Micro-CT and histological staining as well as expression of osteoblastic marker (OPN, Runx2 and OSX). Mechanistically, loss of PKD1 mediated the downregulation of osteoblast markers and impaired osteoblast differentiation through STAT3 and p38 MAPK signaling pathways. Taken together, these results demonstrated that PKD1 contributes to the osteoblast differentiation and bone development via elevation of osteoblast markers through activation of STAT3 and p38 MAPK signaling pathways.

Mechanically stimulated ATP release from murine bone cells is regulated by a balance of injury and repair

“…We found that PLC and PKCµ, known downstream targets of Ca 2+ signaling ( Mochly-Rosen et al, 2012 ), regulated basal vesicle abundance and membrane resealing. Our study suggests that the osteoporotic phenotype reported in PKCµ-deficient bones ( Li et al, 2017 ) may be associated with defective mechanoresponsiveness. Consistent with mechanisms of facilitated membrane resealing ( Togo et al, 1999 ; Cooper and McNeil, 2015 ), we propose that mechanical stimulation results in membrane disruption, which leads to ATP efflux and Ca 2+ influx, triggering vesicular exocytosis and membrane repair that then limits ATP release ( Figure 7 ).…”

Regulation of Osteoclast Differentiation at Multiple Stages by Protein Kinase D Family Kinases

“…Since PKD inhibitors reduce osteoclast function, one might propose they could be used as anti-resorptive therapies. However, due to PKDs' wide tissue distribution and other known physiological roles, we suggest that potential skeletal benefits of long term administration of PKD inhibitors as anti-resorptives may be countered by negative effects on osteoblastic bone formation [57,58], or on other tissues including pancratic β-cells, skeletal muscle, and B-and T-cells; see [59] for a review. Rather, we suggest either that if osteoclast-targeted delivery can be developed or if osteoclast-specific PKD targets can be identified, these might be more viable loci for novel clinical interventions.…”

Protein kinase D1 conditional null mice show minimal bone loss following ovariectomy

“…Effects of PRKD1 deficiency in bone in vivo have been examined previously (Ford et al, 2013,Li et al, 2017,Bollag et al, 2017). The first two studies reported on young animals (4 to 10 weeks old) and found a similar reduction in femoral and whole-body BMD in males and females (Ford et al, 2013) or analyzed a pooled population of both males and females for determination of bone parameters (Li et al, 2017). A differential effect of PRKD1 deficiency on the expression of certain genes was also observed in bone marrow stromal cells derived from males versus females ex vivo (Ford et al, 2013).…”

“…In previous studies the effects of PRKD1 in bone in vivo were examined in young male and female mice pooled for analysis of bone parameters; the results showed an important role of PRKD1 in bone biology (Ford et al, 2013,Li et al, 2017). Our study, in which we demonstrated that PRKD1 ablation resulted in decreased bone formation (Bollag et al, 2017), was confined to mature males to limit any potential confounding effects from skeletal growth or estrogen-related biology.…”