Clinical And Basic Research On Ctsk And Clc-7 Involving In Osteoclast Function

Bone remodelling is an essential process in maintaining bone quality and strength, as well as calcium homeostasis. Remodelling is a cycle of bone resorption by osteoclasts and formation of new bone by osteoblasts. Break of the balance between osteoclasts and osteoblasts will lead to abnormal formation and structure of bone, and then cause a series of bone metabolic disease. In recent years, as the development of cell biology and molecular genetics, the role of osteoclasts in genetic bone disease became clearing. Some studies have shown that more than ten genes, including the voltage-gated chloride channel 7 (CLCN7) and cathepsin K (CTSK), can cause osteoclast dysfunction, which lead to genetic osteosclerosis disease. In order to investigate the role of CTSK and ClC-7 in related disease, provide theoretical basis for the diagnosis, prevention and treatment of related diseases, this study selected three cases caused by CTSK or CLCN7 mutations and did some clinical and basic research.Research on CTSK and pycnodysostosisIn osteoclasts, CTSK is responsible for degradation of bone matrix proteins, and may also act as a potential regulator of apoptosis and senescence, controlling osteoclast numbers. Mutations in the CTSK gene cause a rare autosomal recessive bone disorder called pycnodysostosis. Here we performed a literature retrospective study of 159 pycnodysostosis patients reported since 1996 and found that 33 different CTSK mutations have been found in 59 unrelated pycnodysostosis families. A total of 69.70% of the mutations are missense mutations. The hot mutation spots are found in exons 6 and 7. Short stature, increased bone density, open fontanels and sutures, frontal and parietal bossing, pathologic fractures, obtuse mandibular angle, hypoplasia of jaws, and stubby hands and feet with osteolysis of the distal phalanges are the top eight phenotypes of pycnodysostosis. For the first time, we constructed an online database, which listed all published CTSK mutations since 1996 (http://www.centralmutations.org/Lsdb.php#CTSK).Based on the study of a pycnodysostosis family, the proband of which was misdiagnosed as osteopetrosis for 30 years, we revealed novel compound heterozygous mutations of CTSK gene (p.Trp29X and p.Tyr283Cys), and highlighted the role of oral and craniofacial examinations in the diagnosis of pycnodysostosis. Additionally, for the first time, we used micro CT scanning and histological analysis to reveal the dental characteristic in the patient with pycnodysostosis, and proposed that disappearance of the boundary between cementum and alveolar bone may lead to post extraction osteomyelitis. Immunologic investigation of the patient showed a significantly reduced level of IL-17A in serum and a decreased ratio of helper/suppressor T lymphocytes. Immunotherapy using thymic peptides plus total glucosides of white peony improved immune homeostasis and clinical manifestations of maxillary osteomyelitis. This result indicated that CTSK may play an important role in human immune system and attenuated function of Th 17 cells may be involved in the pathogenesis of osteomyelitis in pycnodysostosis patients.Research on ClC-7 and osteopetrosisClC-7 is a Cl-/H+ antiporter, that it constitutes the major Cl- permeability of osteoclasts, and that it is important in acidification in the resorption pit. Mutations in the CLCN7 gene cause osteopetrosis, which is a heterogeneous group of genetic disorders. Based on its severity, age of onset and means of inheritance, osteopetrosis is classified into three forms: autosomal recessive osteopetrosis (ARO), autosomal dominant osteopetrosis type II (ADO II), and intermediate autosomal recessive osteopetrosis (IARO). In this part, we selected 2 cases caused by CLCN7 mutations and did some clinical and basic research. One patient is the first IARO patient in China with a novel homozygous variant in CLCN7 gene (p.Pro470Leu) and the other is an ADO II patient with a reported heterozygous variant in CLCN7 gene (p.Arg286Trp). The impressive clinical features of these two osteopetrosis patients are root hypoplasia and unerupted tooth germs beside the generally increased bone intensity. We supposed that ClC-7 in tooth cells may contribute directly to the root formation, and its role may depend on position and quantity.ConclusionsIn this study, we performed a literature retrospective study of 159 pycnodysostosis patients and found the genetic characteristics of CTSK mutations and the clinical phenotypes of pycnodysostosis. We constructed an online database, which listed all published CTSK mutations since 1996. Based on the research on three cases caused by CTSK or CLCN7 mutations, we found that CTSK might play an important role in human immune system and cementum formation. Moreover, we suppose that ClC-7 in different tooth cells may contribute directly to the root formation, and its role may depend on position and quantity.