Inactivation of anoctamin-6/Tmem16f, a regulator of phosphatidylserine scrambling in osteoblasts, leads to decreased mineral deposition in skeletal tissues

Abstract

During vertebrate skeletal development, osteoblasts produce a mineralized bone matrix by deposition of hydroxyapatite crystals in the extracellular matrix. Anoctamin6/Tmem16F (Ano6) belongs to a conserved family of transmembrane proteins with chloride channel properties. In addition, Ano6 has been linked to phosphatidylserine (PS) scrambling in the plasma membrane. During skeletogenesis, Ano6 mRNA is expressed in differentiating and mature osteoblasts. Deletion of Ano6 in mice results in reduced skeleton size and skeletal deformities. Molecular analysis revealed that chondrocyte and osteoblast differentiation are not disturbed. However, mutant mice display increased regions of nonmineralized, Ibsp-expressing osteoblasts in the periosteum during embryonic development and increased areas of uncalcified osteoid postnatally. In primary Ano6 À/À osteoblasts, mineralization is delayed, indicating a cell autonomous function of Ano6. Furthermore, we demonstrate that calcium-dependent PS scrambling is impaired in osteoblasts. Our study is the first to our knowledge to reveal the requirement of Ano6 in PS scrambling in osteoblasts, supporting a function of PS exposure in the deposition of hydroxyapatite. ß

TMEM16F is required for phosphatidylserine exposure and microparticle release in activated mouse platelets

“…These results suggest that, under physiological conditions, TMEM16F plays an important role in microparticle shedding. TMEM16F dependency has been similarly observed during bone tissue mineralization (39), during which PtdSer-rich matrix vesicles containing concentrated phosphate and Ca 2+ ions bud off from the plasma membranes (40). Our EM images revealed that the rod-like extensions that formed on the surface of the activated platelets were released in a TMEM16F-dependent manner, consistent with the possibility that microparticle release from the activated platelets is associated with morphological changes.…”

Calcium-dependent Phospholipid Scramblase Activity of TMEM16 Protein Family Members

“…However, of the five TMEM family members (16C, 16D, 16F, 16G, and 16J) that can scramble lipids, only 16F is expressed in muscle, lymphocytes, and bone marrow. In fact, Ehlen et al recently showed that TMEM16F Ϫ/Ϫ osteoblasts lost the ability to scramble PS, leading to the decreased deposition of mineral in the bone tissues (57). It will be interesting to examine whether the other tissues such as muscles and immune system develop normally in TMEM16F Ϫ/Ϫ mice or in patients with Scott syndrome.…”

Anoctamin-6 Controls Bone Mineralization by Activating the Calcium Transporter NCX1

“…During vertebrate skeletal development, specialized cells, the osteoblasts, produce a mineralized bone matrix by deposition of hydroxyapatite crystals in the extracellular collagen matrix, where they become embedded and differentiate into osteocytes (1)(2)(3). This process requires the organized transport of high concentrations of Ca 2ϩ and phosphate ions into the extracellular matrix without inducing premature crystallization.…”