Hypoxia mediates osteocyte ORP150 expression and cell death in vitro

Abstract

Abstract. Skeletal unloading leads to hypoxia in the bone microenvironment, resulting in imbalanced bone remodeling that favors bone resorption. Osteocytes, the mechanosensors of bone, have been demonstrated to orchestrate bone homeostasis. Hypoxic osteocytes either undergo apoptosis or actively stimulate osteoclasts to remove bone matrix during hypoxia. Oxygen-regulated protein 150 (ORP150) is an endoplasmic reticulum-associated chaperone that has been observed to serve an important role in the cellular adaptation to hypoxia and in preventing cellular apoptosis in various tissue types. The current study hypotheses that expression of ORP150 would be increased in osteocytes under hypoxic conditions (1% O 2 ). The MLO-Y4 osteocyte cell line was cultured under normoxic or hypoxic conditions for up to 72 h. It was demonstrated that 1% O 2 significantly induced hypoxia after 16 h and up to 72 h, significantly reduced cell number at 8 and 48 h, induced cell death at 8, 24 and 48 h and induced apoptosis at 16, 24 and 48 h. Significant differences in ORP150 mRNA were observed at 72 h, however no differences were observed in the protein expression levels. The relative increase in ORP150 mRNA observed in hypoxia, compared with normoxia, may support its cytoprotective role in oxygen-deprived conditions.

Osteoarthritic Milieu Affects Adipose‐Derived Mesenchymal Stromal Cells

“…The oxygen percentage was controlled by an Oxygen Analyzer (Vascular Technology, Nashua, NH). Pimonidazole hydrochloride (Hypoxyprobe™‐1 kit; Chemicon, Burlington, MA) is a substance with low molecular weight that binds only to cells that have an oxygen tension of 10 mm Hg (pO2~1,2%) or lower, and was used to evaluate hypoxia of ASC …”

Osteocyte apoptosis: the roles and key molecular mechanisms in resorption-related bone diseases

“…Trigger the generation of pro-inflammatory and pro-osteoclastic factors via positive feedback loop [109][110][111][112]114 FADD Trigger a caspase cascade; induce GCs-induced apoptosis 6,118 Sclerostin Promote osteocyte cells death upon unloading; inhibit bone formation 53,107,108 BNIP3 Promote cell death during hypoxia 60,62 CCN2 Promote osteocyte apoptosis upon excess mechanical stress 33,69 TNF-α Stimulate osteocyte apoptosis upon inflammation and cancer 92,115,116 Caspase-3 Regulate osteocyte apoptosis via physical interactions in mechanistic stimulus 27,127 CTSK Breakdown the bone matrix adjacent to the osteocyte; increase the size of the osteocyte lacunae and mineralization decrease vitality of osteocytes 23 DMP-1 Regulate osteocyte formation and phosphate homeostasis; involve in osteocytic apoptosis 29,84,154 Pyk2 Promote GCs-induced osteocytic apoptosis via focal adhesion 82 Panx-1 Promote fatigue-induced osteocytic apoptosis 160 Anti-apoptotic function SOD2 Suppress aging and loss of bone mass; decrease degeneration of the osteocyte LCN 24,61 AMPK Protects against Hcy-induced osteocyte apoptosis 96,101,102 NO Maintain osteocytic vitality by pulsatile fluid flow 44,54,100…”

Administração sistêmica de rosiglitazona estimula a apoptose de osteócitos e cementócitos, interferindo no desenvolvimento de lesões periapicais induzidas em camundongos

“…Avanços recentes nos estudos da biologia celular no tecido ósseo permitiram também a identificação de diferentes marcadores de membrana, nucleares e citoplasmáticos. Dentre esses marcadores, destacam-se algumas moléculas específicas como fatores de transcrição e outras proteínas relacionadas com o perfil de expressão nos osteócitos, a fim de se determinar o seu estágio de maturação (transição de osteócitos jovens até osteócitos maduros) (Narayanan et al, 2003;Franz-Odendaal et al, 2006;Dallas e Bonewald, 2010;Montesi et al, 2016).…”

“…Esta proteína é associada ao retículo endoplasmático e está presente em osteócitos maduros, embebidos na matriz óssea mineralizada (Montesi et al, 2016).…”

“…Por sua vez, a ORP150 tem sido recentemente estudada por desempenhar um papel importante na adaptação celular à hipóxia e na prevenção de apoptose celular em vários tipos de tecidos. Esta proteína está presente em osteócitos maduros, embebidos na matriz óssea mineralizada (Montesi et al, 2016).…”