Intercellular Communication between Keratinocytes and Fibroblasts Induces Local Osteoclast Differentiation: a Mechanism Underlying Cholesteatoma-Induced Bone Destruction

Abstract

Bone homeostasis is maintained by a balance in activity between bone-resorbing osteoclasts and bone-forming osteoblasts. Shifting the balance toward bone resorption causes osteolytic bone diseases such as rheumatoid arthritis and periodontitis. Osteoclast differentiation is regulated by receptor activator of nuclear factor B ligand (RANKL), which, under some pathological conditions, is produced by T and B lymphocytes and synoviocytes. However, the mechanism underlying bone destruction in other diseases is little understood. Bone destruction caused by cholesteatoma, an epidermal cyst in the middle ear resulting from hyperproliferation of keratinizing squamous epithelium, can lead to lethal complications. In this study, we succeeded in generating a model for cholesteatoma, epidermal cyst-like tissue, which has the potential for inducing osteoclastogenesis in mice. Furthermore, an in vitro coculture system composed of keratinocytes, fibroblasts, and osteoclast precursors was used to demonstrate that keratinocytes stimulate osteoclast differentiation through the induction of RANKL in fibroblasts. Thus, this study demonstrates that intercellular communication between keratinocytes and fibroblasts is involved in the differentiation and function of osteoclasts, which may provide the molecular basis of a new therapeutic strategy for cholesteatoma-induced bone destruction. Bone is a highly dynamic organ in which homeostasis is maintained by a balance in activity between bone-resorbing osteoclasts and bone-forming osteoblasts. An imbalance between osteoclastic and osteoblastic activity causes various skeletal disorders. Osteoclasts are multinucleate cells that differentiate from mononuclear macrophage/monocyte-lineage hematopoietic precursor cells, which are attracted to the bloodstream by factors, including sphingsine-1 phosphate (1, 2). Osteoclast differentiation and function are regulated by macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor B ligand (RANKL) (3-5). Under physiological conditions, osteoblasts or osteocytes are the source of RANKL (6-8). RANKL-mediated osteoclastogenesis also plays an important role in bone destruction in inflammatory bone diseases such as rheumatoid arthritis (RA) or periodontal diseases. In such pathological states, synoviocytes or immune cells, such as B or T lymphocytes, infiltrating into the area are proposed to be the major sources of RANKL (9-11). In RA, infiltration of T helper 17 (Th17) cells is observed in the synovium. Th17 cells indirectly induce RANKL expression in synoviocytes by producing interleukin-17 (IL-17) (12), and Th17 cells themselves express RANKL on their plasma membrane (13). Thus, in many bone destructive diseases, the mechanisms of bone destruction are becoming clarified in detail. However, there are still certain bone destructive diseases whose underlying mechanisms remain to be elucidated. Cholesteatoma, a benign entity arising in temporal bone, is one such disease where our understanding is limited.Cholesteatoma is an epid...

Genome-wide association studies detects candidate genes for wool traits by re-sequencing in Chinese fine-wool sheep

“…The Canonical Wnt signaling pathway dictated the follicle distribution [ 50 ], and is required in the normal skin to guide the differentiation of bulge stem cells into hair cells [ 51 ]. SRC was also enriched into the osteoclast development (GO:0036035), and the interaction between keratinocytes and fibroblasts induces osteoclasto genesis, which in turn can lead to bone resorption [ 52 ]. This process may reduce the toughness of the wool fiber, making it easily breakable.…”

Establishment and validation of an in vitro co-culture model for oral cell lines using human PBMC-derived osteoclasts, osteoblasts, fibroblasts and keratinocytes

“…In order to overcome this problem, Iwamoto et al cultivated keratinocytes and fibroblasts together with OC and could show sufficient RANKL expression to differentiate osteoclasts in a co-culture model. Intercellular communication among the different cell lines involved in the co-culture seems to trigger local RANKL expression 27 .…”

SEM BSE 3D Image Analysis of Human Incus Bone Affected by Cholesteatoma Ascribes to Osteoclasts the Bone Erosion and VpSEM dEDX Analysis Reveals New Bone Formation

“…In some studies [2,3], osteoclast was not observed in resorbing bone areas of incus with CHO; in others [4][5][6][7], they were reported. This is probably due to the transient nature of osteoclasts; they have a relatively short life and, being surgical procedures done after inflammation control, they may be not present at time of sample recovery and fixation.…”

“…Regarding its microstructure CHO is made of matrix (keratinized squamous epithelium), perimatrix (subepithelial connective tissue of variable thickness), and keratin debris. Bone erosion is considered a typical characteristic of cholesteatoma; however, it is still a matter of debate if bone erosion is due to osteoclast action, being present in literature conflicting results [2][3][4][5][6][7]. Scanning electron microscopy is an elective imaging technique for bone ultrastructural studies [8][9][10][11][12], so we observed by means of innovative SEM BSE 3D imaging and VpSEM EDX analysis that cholesteatoma affected incus bone surface, in order to accurately describe their surface modifications and finally assess if osteoclasts are directly responsible for bone resorption.…”