Mechanosensor polycystin-1 potentiates differentiation of human osteoblastic cells by upregulating Runx2 expression via induction of JAK2/STAT3 signaling axis

Abstract

Polycystin-1 (PC1) has been proposed as a chief mechanosensing molecule implicated in skeletogenesis and bone remodeling. Mechanotransduction via PC1 involves proteolytic cleavage of its cytoplasmic tail (CT) and interaction with intracellular pathways and transcription factors to regulate cell function. Here we demonstrate the interaction of PC1-CT with JAK2/STAT3 signaling axis in mechanically stimulated human osteoblastic cells, leading to transcriptional induction of Runx2 gene, a master regulator of osteoblastic differentiation. Primary osteoblast-like PC1-expressing cells subjected to mechanical-stretching exhibited a PC1-dependent increase of the phosphorylated(p)/active form of JAK2. Specific interaction of PC1-CT with pJAK2 was observed after stretching while pre-treatment of cells with PC1 (anti-IgPKD1) and JAK2 inhibitors abolished JAK2 activation. Consistently, mechanostimulation triggered PC1-mediated phosphorylation and nuclear translocation of STAT3. The nuclear phosphorylated(p)/DNA-binding competent pSTAT3 levels were augmented after stretching followed by elevated DNA-binding activity. Pre-treatment with a STAT3 inhibitor either alone or in combination with anti-IgPKD1 abrogated this effect. Moreover, PC1-mediated mechanostimulation induced elevation of Runx2 mRNA levels. ChIP assays revealed direct regulation of Runx2 promoter activity by STAT3/Runx2 after mechanical-stretching that was PC1-dependent. Our findings show that mechanical load upregulates expression of Runx2 gene via potentiation of PC1-JAK2/STAT3 signaling axis, culminating to possibly control osteoblastic differentiation and ultimately bone formation.

Aberrant connective tissue differentiation towards cartilage and bone underlies human keloids in African Americans

“…In chondrogenic and osteoblastic cell lines, RUNX2 has been demonstrated to transactivate type 1 collagen and type X collagen (Col10A1) . Upstream activation of chondrogenic differentiation has been found to be mediated by RUNX2 …”

“…[24] Upstream activation of chondrogenic differentiation has been found to be mediated by RUNX2. [25,26] Thus, the molecular fingerprint of cellular activation in keloids is more related to differentiation of cartilage and bone connective tissues than dermal connective tissue and may be mediated by RUNX2…”

Polycystin-1 interacts with TAZ to stimulate osteoblastogenesis and inhibit adipogenesis

“…This schema proposes that mechanical forces, such as ECM stiffness, flow, and mechanical stretch, activate the PC1/PC2 complex (13,31,50,51,(63)(64)(65)(66), leading to stimulation of intracellular calcium, induction of PC1-CTT cleavage, and TAZ nuclear translocation to enhance Runx2-mediated induction of osteoblast gene transcription and to inhibit PPARγ and adipogenesis (33,39,42,44,46,67). Together this work identifies a new mechanosensing complex and the feasibility of targeting this complex for treating disorders caused by mechanical unloading and ageing.…”

“…Other pathways may also be linked to polycystins. For example, interaction of PC1 with other transcription factors (i.e., NFAT and STAT3) has been described in human osteoblasts that regulate cell proliferation/differentiation via induction of Runx2 (63,64). PC1 is also reported to mediate the response to mechanical strain via potentiation of intracellular calcium and Akt/β-catenin pathways in osteoblasts (65).…”

Polycystins in disease mechanobiology

“…Bone-specific pathways have been documented to be modulated by polycystins, such as the PC1/Janus kinase 2 (JAK2)/STAT3 pathway and the PC1/calcineurin/nuclear factor of activated T-cells (NFAT) pathway. 13,14 In particular, JAK/STAT pathways have been already associated with bone metabolism. 15 Under mechanical stimulation, PC1 seems to activate the JAK2/STAT3 axis to induce the transcription of the osteoblast-specific runx2 transcription factor.…”