Osteocytes as main responders to low-intensity pulsed ultrasound treatment during fracture healing

Abstract

Ultrasound stimulation is a type of mechanical stress, and low-intensity pulsed ultrasound (LIPUS) devices have been used clinically to promote fracture healing. However, it remains unclear which skeletal cells, in particular osteocytes or osteoblasts, primarily respond to LIPUS stimulation and how they contribute to fracture healing. To examine this, we utilized medaka, whose bone lacks osteocytes, and zebrafish, whose bone has osteocytes, as in vivo models. Fracture healing was accelerated by ultrasound stimulation in zebrafish, but not in medaka. To examine the molecular events induced by LIPUS stimulation in osteocytes, we performed RNA sequencing of a murine osteocytic cell line exposed to LIPUS. 179 genes reacted to LIPUS stimulation, and functional cluster analysis identified among them several molecular signatures related to immunity, secretion, and transcription. Notably, most of the isolated transcription-related genes were also modulated by LIPUS in vivo in zebrafish. However, expression levels of early growth response protein 1 and 2 (Egr1, 2), JunB, forkhead box Q1 (FoxQ1), and nuclear factor of activated T cells c1 (NFATc1) were not altered by LIPUS in medaka, suggesting that these genes are key transcriptional regulators of LIPUS-dependent fracture healing via osteocytes. We therefore show that bone-embedded osteocytes are necessary for LIPUS-induced promotion of fracture healing via transcriptional control of target genes, which presumably activates neighboring cells involved in fracture healing processes.

Emerging roles of growth factors in osteonecrosis of the femoral head

“…Overexpression of miR-23a-3p inhibits and its downregulation enhances the osteogenic differentiation of BMSCs (Dai et al, 2019). Consistent with previous studies, Zhang X. Y. et al (2021) reported that miR-23a-3p expression was significantly increased in rat models of ONFH. In addition, miR-23a knockdown promoted the viability and osteogenic differentiation of BMSCs and increased the mRNA and protein expression of BMP-2, BMP-4, Runx2, Smad5, Wnt1, and β-catenin in BMSCs and rat models of ONFH.…”

“…Low-intensity pulsed ultrasonography (LIPUS) can enhance osteogenic differentiation of MSCs, stimulate the differentiation and proliferation of osteoblasts, inhibit osteoclasts, improve local blood perfusion and angiogenesis, and accelerate the healing of stress fractures ( Chan et al, 2006 ; Amini et al, 2020 ). Clinical studies have shown significant positive effects of LIPUS in treating fresh ( Shimizu et al, 2021 ) and nonunion ( Jiang et al, 2019 ; Leighton et al, 2021 ) fractures. In addition, LIPUS is considered a non-invasive treatment strategy for ONFH ( Yan et al, 2011 ).…”

From the Matrix to the Nucleus and Back: Mechanobiology in the Light of Health, Pathologies, and Regeneration of Oral Periodontal Tissues

“…LIPUS was shown to enhance ECM synthesis and regeneration and to be a potent stimulator of osteogenic differentiation and is used, e.g., in the context of fracture healing [327][328][329]. Bone mass and maturation is also increased upon LIPUS treatment in different animal models, and it was shown that osteocytes in particular respond to LIPUS treatment [330,331]. Transcriptional analysis in a mouse cell line revealed that approximately 180 genes from clusters related to transcription, cellular secretion and immunity are responsive to the mechanical stimulation [331].…”

“…Bone mass and maturation is also increased upon LIPUS treatment in different animal models, and it was shown that osteocytes in particular respond to LIPUS treatment [330,331]. Transcriptional analysis in a mouse cell line revealed that approximately 180 genes from clusters related to transcription, cellular secretion and immunity are responsive to the mechanical stimulation [331].…”

Research trends and progress in the field of metal materials and bone repair: Comprehensive bibliometric and visual analysis (2012–2021)

“…However, the outcomes of implantation and repair relying only on bone-like frames are not ideal, which is also the reason why there has been no breakthrough in the treatment of bone defects in the past 30 years. Therefore, scholars have not only continued related research in the fields of medicine and biology but also performed related research in the fields of acoustics (Shimizu et al, 2021), optics (Bai et al, 2021), heat (Shu and Sugita, 2020), and others.…”