Survival of children with chronic medical illnesses is leading to an increase in secondary osteoporosis due to impaired peak bone mass （PBM）. Insulin-like growth factor type Ⅰ （IGF-1） levels correlate with the pa...Survival of children with chronic medical illnesses is leading to an increase in secondary osteoporosis due to impaired peak bone mass （PBM）. Insulin-like growth factor type Ⅰ （IGF-1） levels correlate with the pattern of bone mass accrual and many chronic illnesses are associated with low IGF-1 levels. Reduced serum levels of IGF-1 minimally affect the integrity of the skeleton, whereas recent studies suggest that skeletal IGF-I regulates PBM. To determine the role of IGF-1 in postnatal bone mass accrual regardless of source, we established an inducible type 1 Igf receptor Cre/lox knockout mouse model, in which the type 1 Igf receptor was deleted inducibely in the mesenchymal stem cells （MSCs） from 3-7 weeks of age. The size of the mouse was not affected as knockout and wild type mice had similar body weights and nasoanal and femoral lengths. However, bone volume and trabecular bone thickness were decreased in the secondary spongiosa of female knockout mice relative to wild type controls, indicating that IGF-1 is critical for bone mass. IGF-1 signaling in MSCs in vitro has been implicated to be involved in both migration to the bone surface and differentiation into bone forming osteoblasts. To clarify the exact role of IGF-1 in bone, we found by immunohistochemical analysis that a similar number of Osterix-positive osteoprogenitors were on the bone perimeter, indicating migration of MSCs was not affected. Most importantly, 56% fewer osteocalcin-positive mature osteoblasts were present on the bone perimeter in the secondary spongiosa in knockout mice versus wild type littermates. These in vivo data demonstrate that the primary role of skeletal IGF-1 is for the terminal differentiation of osteoprogenitors, but refute the role of IGF-1 in MSC migration in vivo. Additionally, these findings confirm that impaired IGF-1 signaling in bone MSCs is sufficient to impair bone mass acquisition.展开更多
Parathyroid hormone(PTH) regulates bone remodeling by activating PTH type 1 receptor(PTH1R) in osteoblasts/osteocytes. Insulinlike growth factor type 1(IGF-1) stimulates mesenchymal stem cell differentiation to osteob...Parathyroid hormone(PTH) regulates bone remodeling by activating PTH type 1 receptor(PTH1R) in osteoblasts/osteocytes. Insulinlike growth factor type 1(IGF-1) stimulates mesenchymal stem cell differentiation to osteoblasts. However, little is known about the signaling mechanisms that regulates the osteoblast-to-osteocyte transition. Here we report that PTH and IGF-I synergistically enhance osteoblast-to-osteocyte differentiation. We identified that a specific tyrosine residue, Y494, on the cytoplasmic domain of PTH1R can be phosphorylated by insulin-like growth factor type I receptor(IGF1R) in vitro. Phosphorylated PTH1R localized to the barbed ends of actin filaments and increased actin polymerization during morphological change of osteoblasts into osteocytes.Disruption of the phosphorylation site reduced actin polymerization and dendrite length. Mouse models with conditional ablation of PTH1R in osteoblasts demonstrated a reduction in the number of osteoctyes and dendrites per osteocyte, with complete overlap of PTH1R with phosphorylated-PTH1R positioning in osteocyte dendrites in wild-type mice. Thus, our findings reveal a novel signaling mechanism that enhances osteoblast-to-osteocyte transition by direct phosphorylation of PTH1R by IGF1R.展开更多
Irradiation induces bone injury by generating free radicals that adversely affect the microenvironment for Mesenchymal stem cells (MSCs) and damages bone marrow blood vessels. We wished to investigate the efficacy of ...Irradiation induces bone injury by generating free radicals that adversely affect the microenvironment for Mesenchymal stem cells (MSCs) and damages bone marrow blood vessels. We wished to investigate the efficacy of antioxidant administration in protecting stem cell microenvironments and promoting bone marrow vasculature recovery after radiation treatment. The antioxidant ascorbic acid was administered 3 times at a dosage: 150 mg/kg/day to experimenttal groups 3 days before targeted radiation by a unique Small Animal Radiation Research Platform (SARRP). Histological staining indicated that antioxidant treated mice had less severe bone marrow damage 1 week after irradiation with substantial marrow cellular recovery 4 weeks later. Flow cytometry analysis showed that antioxidant administration was correlated with a rebound in MSC quantity in bone marrow. Anti-oxidant treatment was also observed to allow for better vasculature retention and recovery through angiographic imaging. Our data suggests that pre-treatment with ascorbic acid serves to improve bone marrow microenvironments for bone marrow stem cells after radiation treatment.展开更多
基金supported in part by the grants from the United States National Institute of Health NIDDK including T32DK07751 (JLC)the Diabetes Research and Training Center grant P60DK079637(JSF),and DK057501 and DK08098 (XC)
文摘Survival of children with chronic medical illnesses is leading to an increase in secondary osteoporosis due to impaired peak bone mass （PBM）. Insulin-like growth factor type Ⅰ （IGF-1） levels correlate with the pattern of bone mass accrual and many chronic illnesses are associated with low IGF-1 levels. Reduced serum levels of IGF-1 minimally affect the integrity of the skeleton, whereas recent studies suggest that skeletal IGF-I regulates PBM. To determine the role of IGF-1 in postnatal bone mass accrual regardless of source, we established an inducible type 1 Igf receptor Cre/lox knockout mouse model, in which the type 1 Igf receptor was deleted inducibely in the mesenchymal stem cells （MSCs） from 3-7 weeks of age. The size of the mouse was not affected as knockout and wild type mice had similar body weights and nasoanal and femoral lengths. However, bone volume and trabecular bone thickness were decreased in the secondary spongiosa of female knockout mice relative to wild type controls, indicating that IGF-1 is critical for bone mass. IGF-1 signaling in MSCs in vitro has been implicated to be involved in both migration to the bone surface and differentiation into bone forming osteoblasts. To clarify the exact role of IGF-1 in bone, we found by immunohistochemical analysis that a similar number of Osterix-positive osteoprogenitors were on the bone perimeter, indicating migration of MSCs was not affected. Most importantly, 56% fewer osteocalcin-positive mature osteoblasts were present on the bone perimeter in the secondary spongiosa in knockout mice versus wild type littermates. These in vivo data demonstrate that the primary role of skeletal IGF-1 is for the terminal differentiation of osteoprogenitors, but refute the role of IGF-1 in MSC migration in vivo. Additionally, these findings confirm that impaired IGF-1 signaling in bone MSCs is sufficient to impair bone mass acquisition.
基金provided by K01-AR060433 (T.Q.)K08-AR064833 (J.C)R01-AR063943 (X.C)
文摘Parathyroid hormone(PTH) regulates bone remodeling by activating PTH type 1 receptor(PTH1R) in osteoblasts/osteocytes. Insulinlike growth factor type 1(IGF-1) stimulates mesenchymal stem cell differentiation to osteoblasts. However, little is known about the signaling mechanisms that regulates the osteoblast-to-osteocyte transition. Here we report that PTH and IGF-I synergistically enhance osteoblast-to-osteocyte differentiation. We identified that a specific tyrosine residue, Y494, on the cytoplasmic domain of PTH1R can be phosphorylated by insulin-like growth factor type I receptor(IGF1R) in vitro. Phosphorylated PTH1R localized to the barbed ends of actin filaments and increased actin polymerization during morphological change of osteoblasts into osteocytes.Disruption of the phosphorylation site reduced actin polymerization and dendrite length. Mouse models with conditional ablation of PTH1R in osteoblasts demonstrated a reduction in the number of osteoctyes and dendrites per osteocyte, with complete overlap of PTH1R with phosphorylated-PTH1R positioning in osteocyte dendrites in wild-type mice. Thus, our findings reveal a novel signaling mechanism that enhances osteoblast-to-osteocyte transition by direct phosphorylation of PTH1R by IGF1R.
文摘Irradiation induces bone injury by generating free radicals that adversely affect the microenvironment for Mesenchymal stem cells (MSCs) and damages bone marrow blood vessels. We wished to investigate the efficacy of antioxidant administration in protecting stem cell microenvironments and promoting bone marrow vasculature recovery after radiation treatment. The antioxidant ascorbic acid was administered 3 times at a dosage: 150 mg/kg/day to experimenttal groups 3 days before targeted radiation by a unique Small Animal Radiation Research Platform (SARRP). Histological staining indicated that antioxidant treated mice had less severe bone marrow damage 1 week after irradiation with substantial marrow cellular recovery 4 weeks later. Flow cytometry analysis showed that antioxidant administration was correlated with a rebound in MSC quantity in bone marrow. Anti-oxidant treatment was also observed to allow for better vasculature retention and recovery through angiographic imaging. Our data suggests that pre-treatment with ascorbic acid serves to improve bone marrow microenvironments for bone marrow stem cells after radiation treatment.
