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Thyrostimulin Regulates Osteoblastic Bone Formation During Early Skeletal Development.

Bassett JH, van der Spek A, Logan JG, Gogakos A, Bagchi-Chakraborty J, Murphy E, van Zeijl C, Down J, Croucher PI, Boyde A, Boelen A, Williams GR - Endocrinology (2015)

Bottom Line: However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts.Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro.These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

View Article: PubMed Central - PubMed

Affiliation: Molecular Endocrinology Laboratory (J.H.D.B., J.G.L., A.G., J.B.C., E.M., G.R.W.), Department of Medicine, Imperial College London, London, W12 0NN United Kingdom; Department of Endocrinology (A.v.d.S., C.v.Z., A.Boe.), Academic Medical Centre, University of Amsterdam, 1100 DD Amsterdam, The Netherlands; Bone Biology Program (J.D., P.I.C.), Garvan Institute of Medical Research, Sydney, NSW 2010 Australia; and Centre for Oral Growth and Development (A.Boy.), Queen Mary, University of London, London, E1 4NS United Kingdom.

ABSTRACT
The ancestral glycoprotein hormone thyrostimulin is a heterodimer of unique glycoprotein hormone subunit alpha (GPA)2 and glycoprotein hormone subunit beta (GPB)5 subunits with high affinity for the TSH receptor. Transgenic overexpression of GPB5 in mice results in cranial abnormalities, but the role of thyrostimulin in bone remains unknown. We hypothesized that thyrostimulin exerts paracrine actions in bone and determined: 1) GPA2 and GPB5 expression in osteoblasts and osteoclasts, 2) the skeletal consequences of thyrostimulin deficiency in GPB5 knockout (KO) mice, and 3) osteoblast and osteoclast responses to thyrostimulin treatment. Gpa2 and Gpb5 expression was identified in the newborn skeleton but declined rapidly thereafter. GPA2 and GPB5 mRNAs were also expressed in primary osteoblasts and osteoclasts at varying concentrations. Juvenile thyrostimulin-deficient mice had increased bone volume and mineralization as a result of increased osteoblastic bone formation. However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts. Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro. These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

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Micro-CT. A, Micro-CT images of the distal femoral metaphysis from P42 WT and GPB5KO mice. B, Graphs showing BV/TV, trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular spacing (Tb.Sp), structure model index (SMI) (an indicator of trabecular shape, in which pure rod-like shape = 3, pure plate-like = 0), and connectivity density (Conn.D) (mean ± SEM) in distal femur trabecular bone from P42 WT and GPB5KO mice. C, Micro-CT images of the middiaphyseal femur cortical bone from P42 WT and GPB5KO mice. D, Graphs showing total cross-sectional area of cortical bone inside the periosteal envelope (Tt.Ar), cortical bone area (Ct.Ar), cortical area fraction (Ct.Ar/Tt.Ar), cortical BV, cortical bone volume fraction (BV/TV), and average cortical thickness (Ct.Th) (mean ± SEM) in middiaphyseal femur from P42 WT and GPB5KO mice. Student's t test, GPB5KO vs WT; *, P < .05; **, P < .01 (n = 3 per genotype, per gender). Scale bars, 200 μm.
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Figure 4: Micro-CT. A, Micro-CT images of the distal femoral metaphysis from P42 WT and GPB5KO mice. B, Graphs showing BV/TV, trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular spacing (Tb.Sp), structure model index (SMI) (an indicator of trabecular shape, in which pure rod-like shape = 3, pure plate-like = 0), and connectivity density (Conn.D) (mean ± SEM) in distal femur trabecular bone from P42 WT and GPB5KO mice. C, Micro-CT images of the middiaphyseal femur cortical bone from P42 WT and GPB5KO mice. D, Graphs showing total cross-sectional area of cortical bone inside the periosteal envelope (Tt.Ar), cortical bone area (Ct.Ar), cortical area fraction (Ct.Ar/Tt.Ar), cortical BV, cortical bone volume fraction (BV/TV), and average cortical thickness (Ct.Th) (mean ± SEM) in middiaphyseal femur from P42 WT and GPB5KO mice. Student's t test, GPB5KO vs WT; *, P < .05; **, P < .01 (n = 3 per genotype, per gender). Scale bars, 200 μm.

Mentions: Micro-CT analysis of femurs from juvenile animals demonstrated increased trabecular bone volume, number and connectivity, reduced trabecular spacing and more plate-like morphology in male GPB5KO mice (Figure 4, A and B). Trabecular bone parameters did not differ in female GPB5KO mice compared with WT. Juvenile male GPB5KO mice also had increased cortical bone area, volume and thickness but no differences were seen in females (Figure 4, C and D). Cortical bone porosity did not differ in juvenile GPB5KO mice of either gender compared with WT (male 1.15 ± 0.04% vs 1.07 ± 0.13%, P = .59; female 0.19 ± 0.04% vs 0.40 ± 0.13%, P = .19). qBSE-SEM demonstrated increased trabecular bone mineralization in juvenile female GPB5KO mice and increased cortical bone mineralization in juveniles of both genders (Figure 5).


Thyrostimulin Regulates Osteoblastic Bone Formation During Early Skeletal Development.

Bassett JH, van der Spek A, Logan JG, Gogakos A, Bagchi-Chakraborty J, Murphy E, van Zeijl C, Down J, Croucher PI, Boyde A, Boelen A, Williams GR - Endocrinology (2015)

Micro-CT. A, Micro-CT images of the distal femoral metaphysis from P42 WT and GPB5KO mice. B, Graphs showing BV/TV, trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular spacing (Tb.Sp), structure model index (SMI) (an indicator of trabecular shape, in which pure rod-like shape = 3, pure plate-like = 0), and connectivity density (Conn.D) (mean ± SEM) in distal femur trabecular bone from P42 WT and GPB5KO mice. C, Micro-CT images of the middiaphyseal femur cortical bone from P42 WT and GPB5KO mice. D, Graphs showing total cross-sectional area of cortical bone inside the periosteal envelope (Tt.Ar), cortical bone area (Ct.Ar), cortical area fraction (Ct.Ar/Tt.Ar), cortical BV, cortical bone volume fraction (BV/TV), and average cortical thickness (Ct.Th) (mean ± SEM) in middiaphyseal femur from P42 WT and GPB5KO mice. Student's t test, GPB5KO vs WT; *, P < .05; **, P < .01 (n = 3 per genotype, per gender). Scale bars, 200 μm.
© Copyright Policy - open-access
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Show All Figures
getmorefigures.php?uid=PMC4541616&req=5

Figure 4: Micro-CT. A, Micro-CT images of the distal femoral metaphysis from P42 WT and GPB5KO mice. B, Graphs showing BV/TV, trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular spacing (Tb.Sp), structure model index (SMI) (an indicator of trabecular shape, in which pure rod-like shape = 3, pure plate-like = 0), and connectivity density (Conn.D) (mean ± SEM) in distal femur trabecular bone from P42 WT and GPB5KO mice. C, Micro-CT images of the middiaphyseal femur cortical bone from P42 WT and GPB5KO mice. D, Graphs showing total cross-sectional area of cortical bone inside the periosteal envelope (Tt.Ar), cortical bone area (Ct.Ar), cortical area fraction (Ct.Ar/Tt.Ar), cortical BV, cortical bone volume fraction (BV/TV), and average cortical thickness (Ct.Th) (mean ± SEM) in middiaphyseal femur from P42 WT and GPB5KO mice. Student's t test, GPB5KO vs WT; *, P < .05; **, P < .01 (n = 3 per genotype, per gender). Scale bars, 200 μm.
Mentions: Micro-CT analysis of femurs from juvenile animals demonstrated increased trabecular bone volume, number and connectivity, reduced trabecular spacing and more plate-like morphology in male GPB5KO mice (Figure 4, A and B). Trabecular bone parameters did not differ in female GPB5KO mice compared with WT. Juvenile male GPB5KO mice also had increased cortical bone area, volume and thickness but no differences were seen in females (Figure 4, C and D). Cortical bone porosity did not differ in juvenile GPB5KO mice of either gender compared with WT (male 1.15 ± 0.04% vs 1.07 ± 0.13%, P = .59; female 0.19 ± 0.04% vs 0.40 ± 0.13%, P = .19). qBSE-SEM demonstrated increased trabecular bone mineralization in juvenile female GPB5KO mice and increased cortical bone mineralization in juveniles of both genders (Figure 5).

Bottom Line: However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts.Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro.These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

View Article: PubMed Central - PubMed

Affiliation: Molecular Endocrinology Laboratory (J.H.D.B., J.G.L., A.G., J.B.C., E.M., G.R.W.), Department of Medicine, Imperial College London, London, W12 0NN United Kingdom; Department of Endocrinology (A.v.d.S., C.v.Z., A.Boe.), Academic Medical Centre, University of Amsterdam, 1100 DD Amsterdam, The Netherlands; Bone Biology Program (J.D., P.I.C.), Garvan Institute of Medical Research, Sydney, NSW 2010 Australia; and Centre for Oral Growth and Development (A.Boy.), Queen Mary, University of London, London, E1 4NS United Kingdom.

ABSTRACT
The ancestral glycoprotein hormone thyrostimulin is a heterodimer of unique glycoprotein hormone subunit alpha (GPA)2 and glycoprotein hormone subunit beta (GPB)5 subunits with high affinity for the TSH receptor. Transgenic overexpression of GPB5 in mice results in cranial abnormalities, but the role of thyrostimulin in bone remains unknown. We hypothesized that thyrostimulin exerts paracrine actions in bone and determined: 1) GPA2 and GPB5 expression in osteoblasts and osteoclasts, 2) the skeletal consequences of thyrostimulin deficiency in GPB5 knockout (KO) mice, and 3) osteoblast and osteoclast responses to thyrostimulin treatment. Gpa2 and Gpb5 expression was identified in the newborn skeleton but declined rapidly thereafter. GPA2 and GPB5 mRNAs were also expressed in primary osteoblasts and osteoclasts at varying concentrations. Juvenile thyrostimulin-deficient mice had increased bone volume and mineralization as a result of increased osteoblastic bone formation. However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts. Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro. These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

Show MeSH
Related in: MedlinePlus