Fine-tuning osteoclastogenesis: An insight into the cellular and molecular regulation of osteoclastogenesis.

Osteoclasts, the bone-resorbing cells, are essential for the bone remodeling process and are involved in the pathophysiology of several bone-related diseases. The extensive corpus of in vitro research and crucial mouse model studies in the 1990s demonstrated the key roles of monocyte/macrophage colony-stimulating factor, receptor activator of nuclear factor kappa B ligand (RANKL) and integrin αvß3 in osteoclast biology. Our knowledge of the molecular mechanisms by which these variables control osteoclast differentiation and function has significantly advanced in the first decade of this century. Recent developments have revealed a number of novel insights into the fundamental mechanisms governing the differentiation and functional activity of osteoclasts; however, these mechanisms have not yet been adequately documented. Thus, in the present review, we discuss various regulatory factors including local and hormonal factors, innate as well as adaptive immune cells, noncoding RNAs (ncRNAs), etc., in the molecular regulation of the intricate and tightly regulated process of osteoclastogenesis. ncRNAs have a critical role as epigenetic controllers of osteoclast physiologic activities, including differentiation and bone resorption. The primary ncRNAs, which include micro-RNAs, circular RNAs, and long noncoding RNAs, form a complex network that affects gene transcription activities associated with osteoclast biological activity. Greater knowledge of the involvement of ncRNAs in osteoclast biological activities will contribute to the treatment and management of several skeletal diseases such as osteoporosis, osteoarthritis, rheumatoid arthritis, etc. Moreover, we further outline potential therapies targeting these regulatory pathways of osteoclastogenesis in distinct bone pathologies.

Peritoneal malignant mesothelioma: Slippery like an eel to diagnose on cytology-case series of 3 cases.

INTRODUCTION: Peritoneal malignant mesothelioma is an extremely rare tumor and is a difficult diagnosis to be made on cytology alone. We report 3 cases where the cytologic features were misdiagnosed as carcinoma/lymphoma but histopathology and immunohistochemistry (IHC) established the diagnosis of malignant mesothelioma. CLINICAL DETAILS: Case 1 was a 60-year-old man with multiloculated ascites and omental caking. Peritoneal fluid was reported as malignant on cytology but was misclassified as adenocarcinoma. Case 2, a 45-year-old man with ascites and peritoneal nodularity, radiologically mimicking peritoneal carcinomatosis, was also reported positive for malignancy on ascitic fluid cytology. Fine-needle aspiration (FNAC) from omental fat revealed signet ring cells, thus misleading to cytologic diagnosis of adenocarcinoma. Case 3 was a 63-year-old man with perisplenic mass with extensive omental caking and peritoneal nodularity that was also suspected to be peritoneal carcinomatosis on radiology. FNAC smears from perisplenic mass showed sheets of plasmacytoid cells. On cytology, the differential diagnoses offered were neuroendocrine tumor or non-Hodgkin lymphoma. The diagnosis of malignant mesothelioma was established only after IHC on histopathologic sections in all these cases. None of our patients had history of prior asbestos exposure. CONCLUSION: In such clinical scenarios, with radiology suggesting peritoneal carcinomatosis, the cytologic features need corroboration by IHC/fluorescence in situ hybridization on cell block or biopsy to correctly identify malignant mesothelioma and differentiate it from metastatic carcinomatous deposits and benign mesothelial proliferation.

IL-3 promotes osteoblast differentiation and bone formation in human mesenchymal stem cells.

IL-3 is an important cytokine that regulates hematopoiesis. We have previously demonstrated that IL-3 is a potent inhibitor of osteoclastogenesis and bone resorption. In the present study, we have investigated the role of IL-3 on human osteoblast differentiation and bone formation. We found that IL-3 in a dose-dependent manner increases osteoblast differentiation and matrix mineralization in human mesenchymal stem cells (MSCs). IL-3 significantly enhances the expression of osteoblast specific genes such as alkaline phosphatase, collagen type-I, osteocalcin and osteopontin; and Runx-2 and osterix transcription factors. Moreover, IL-3 induces the expression of bone morphogenetic protein-2 (BMP-2), and activates smad1/5/8. IL-3 enhances osteoblast differentiation and BMP-2 secretion through JAK/STAT pathway. Interestingly, IL-3 promotes in vivo bone regeneration ability of MSCs. Thus, we reveal for the first time that IL-3 enhances human osteoblast differentiation and bone formation in both in vitro and in vivo conditions, and suggest its therapeutic potential for bone formation in important bone diseases.

IL-3 attenuates collagen-induced arthritis by modulating the development of Foxp3+ regulatory T cells.

IL-3, a cytokine secreted by Th cells, functions as a link between the immune and the hematopoietic system. We previously demonstrated the potent inhibitory role of IL-3 on osteoclastogenesis, pathological bone resorption, and inflammatory arthritis. In this study, we investigated the novel role of IL-3 in development of regulatory T (Treg) cells. We found that IL-3 in a dose-dependent manner increases the percentage of Foxp3(+) Treg cells indirectly through secretion of IL-2 by non-Treg cells. These IL-3-expanded Treg cells are competent in suppressing effector T cell proliferation. Interestingly, IL-3 treatment significantly reduces the severity of arthritis and restores the loss of Foxp3(+) Treg cells in thymus, lymph nodes, and spleen in collagen-induced arthritis mice. Most significantly, we show that IL-3 decreases the production of proinflammatory cytokines IL-6, IL-17A, TNF-α, and IL-1 and increases the production of anti-inflammatory cytokines IFN-γ and IL-10 in collagen-induced arthritis mice. Thus, to our knowledge, we provide the first evidence that IL-3 play an important role in modulation of Treg cell development in both in vitro and in vivo conditions, and we suggest its therapeutic potential in the treatment of rheumatoid arthritis and other autoimmune diseases.

Irreversible inhibition of RANK expression as a possible mechanism for IL-3 inhibition of RANKL-induced osteoclastogenesis.

IL-3, a cytokine secreted by activated T lymphocytes, stimulates the proliferation, differentiation and survival of pluripotent hematopoietic stem cells. In this study, we investigated the mechanism of inhibitory action of IL-3 on osteoclast differentiation. We show here that IL-3 significantly inhibits receptor activator of NF-kappaB (RANK) ligand (RANKL)-induced activation of c-Jun N-terminal kinase (JNK). IL-3 down-regulates expression of c-Fos and nuclear factor of activated T cells (NFATc1) transcription factors. In addition, IL-3 down-regulates RANK expression posttranscriptionally in both purified osteoclast precursors and whole bone marrow cells. Furthermore, the inhibitory effect of IL-3 on RANK expression was irreversible. Interestingly, IL-3 inhibits in vivo RANK expression in mice. Thus, we provide the first evidence that IL-3 irreversibly inhibits RANK expression that results in inhibition of important signaling molecules induced by RANKL.

IL-3 inhibits human osteoclastogenesis and bone resorption through downregulation of c-Fms and diverts the cells to dendritic cell lineage.

IL-3 is an important cytokine that regulates hematopoiesis and functions as a link between the immune and the hematopoietic system. In this study, we investigated the role and mechanism of IL-3 action on human osteoclast formation and bone resorption using PBMCs. PBMCs differentiate into functional osteoclasts in the presence of M-CSF and receptor activator of NF-kappaB ligand as evaluated by 23c6 expression and bone resorption. We found that IL-3 dose-dependently inhibited formation of 23c6-positive osteoclasts, bone resorption and C-terminal telopeptide of type I collagen, a collagen degradation product. The inhibitory effect of IL-3 on bone resorption was irreversible. To investigate the mechanism of IL-3 action, we analyzed the effect of IL-3 on the receptor activator of NF-kappaB and c-Fms receptors and c-Fos, PU.1, NFAT cytoplasmic 1, and RelB transcription factors essential for osteoclastogenesis. IL-3 significantly inhibited c-Fms and downregulated both PU.1 and c-Fos at both mRNA and protein level. Furthermore, IL-3-treated cells showed increased expression of dendritic cell markers CD1a and CD80 and decreased expression of monocyte/macrophage marker CD14. Interestingly, IL-3 inhibited formation of human osteoclasts derived from blood monocytes and bone marrow cells of osteoporotic individuals. Thus, IL-3 may have therapeutic potential as an antiosteolytic agent in treatment of osteoporosis.

Human gingiva-derived mesenchymal stem cells are superior to bone marrow-derived mesenchymal stem cells for cell therapy in regenerative medicine.

Mesenchymal stem cells (MSCs) are capable of self-renewal and differentiation into multiple cell lineages. Presently, bone marrow is considered as a prime source of MSCs; however, there are some drawbacks and limitations in use of these MSCs for cell therapy. In this study, we demonstrate that human gingival tissue-derived MSCs have several advantages over bone marrow-derived MSCs. Gingival MSCs are easy to isolate, homogenous and proliferate faster than bone marrow MSCs without any growth factor. Importantly, gingival MSCs display stable morphology and do not loose MSC characteristic at higher passages. In addition, gingival MSCs maintain normal karyotype and telomerase activity in long-term cultures, and are not tumorigenic. Thus, we reveal that human gingiva is a better source of MSCs than bone marrow, and large number of functionally competent clinical grade MSCs can be generated in short duration for cell therapy in regenerative medicine and tissue engineering.