Multiple increased osteoclast functions in individuals with neurofibromatosis type 1

Abstract

Skeletal abnormalities including scoliosis, tibial dysplasia, sphenoid wing dysplasia, and decreased bone mineral density (BMD) are associated with neurofibromatosis type 1 (NF1). We report the cellular phenotype of NF1 human-derived osteoclasts and compare the in vitro findings with the clinical phenotype.Functional characteristics (e.g. osteoclast formation, migration, adhesion, resorptive capacity) and cellular mechanistic alterations (e.g. F-actin polymerization, MAPK phosphorylation, RhoGTPase activity) from osteoclasts cultured from peripheral blood of individuals with NF1 (N=75) were assessed. Osteoclast formation was compared to phenotypic, radiologic, and biochemical data.NF1 osteoprogenitor cells demonstrated increased osteoclast forming capacity. Human NF1-derived osteoclasts demonstrated increased migration, adhesion, and in vitro bone resorption. These activities coincided with increased actin belt formation and hyperactivity in MAPK and RhoGTPase pathways. Although osteoclast formation was increased, no direct correlation of osteoclast formation with BMD, markers of bone resorption, or the clinical skeletal phenotype was observed suggesting that osteoclast formation in vitro cannot directly predict NF1 skeletal phenotypes.While NF1 haploinsufficiency produces a generalized osteoclast gain-in-function and may contribute to increased bone resorption, reduced BMD, and focal skeletal defects associated with

Partial Blindness to Submicron Topography in <b><i>NF1</i></b> Haploinsufficient Cultured Fibroblasts Indicates a New Function of Neurofibromin in Regulation of Mechanosensoric

“…Moreover, experiments by others demonstrated that actin filament dynamics is affected by a reduced neurofibromin dose in human fibrosarcoma cell line via changes in the Rho-ROCK-LIMK2-Cofilin pathway [Ozawa et al, 2005]. The increased actin belt formation in human-derived cultured NF1 +/-osteoclasts is also a consequence of the hyperactivity RhoGTPase pathway [Stevenson et al, 2011]. These observations suggest that a NF1 haploinsufficiency might cause an altered organization and assembly of cytoskeletal proteins, which may affect cell mechanical properties of the cells.…”

“…the production of melanin in melanocytes [Kaufmann et al, 1991;De Schepper et al, 2005], of osteopontin in osteoblasts [Li et al, 2009], of FGF-2, PDGF and midkine in Schwann cells [Mashour et al, 2001], or of collagen in fibroblasts [Yang et al, 2006]. Some NF1 +/-cells display more variable sizes and shapes than their NF1 +/+ counterparts, when they are cultured on surfaces with high stiffness such as Schwann cells [Rosenbaum et al, 2000], keratinocytes [Koivunen et al, 2000;Korkiamäki et al, 2002] or osteoclasts [Heervä et al, 2010;Stevenson et al, 2011]. Several findings demonstrate alterations in the cytoskeletal organization by NF1 haploinsufficiency.…”

“…Cytoskeletal actin abnormalities were observed in Nf1 +/-astrocytes [Gutman et al, 2001]. An increased actin belt formation was shown in human derived cultured NF1 +/-osteoclasts [Heervä et al, 2010;Stevenson et al, 2011]. In cultured NF1 +/-melanocytes, an increased variation of dendrite formation was found [Kemkemer et al, 2002].…”

Valosin-containing protein and neurofibromin interact to regulate dendritic spine density

“…The function of neurofibromin in synaptogenesis (9) and formation of barrel cortex (13) may partially explain these neurological symptoms. It is also known that neurofibromin regulates the functions of osteoclast (14,15) and skeletal muscle development (16). Although the Ras/MAPK pathway, the downstream signaling of neurofibromin, has been implicated in bone resorption (17), the detailed mechanism underlying the bony defects in patients with NF1 remains elusive.…”

Approaches to Treating NF1 Tibial Pseudarthrosis

“…Nitrogen bisphosphonates could theoretically have utility in NF1-related pseudarthrosis management because of the documented overactivity of NF1 osteoclasts, 12,13 and on the osteoclastogenic properties of BMP-2. Bisphosphonates act on the mevalonate pathway, the inhibition of which can reduce MAPK activation due to the lack of correct membrane localization of small GTPases.…”