IADR Abstract Archives
Osteoblast lineage-intrinsic Tsc1 regulates Osteogenesis and Bone Marrow Adipogenesis
Objectives: To determine the physiological roles of TSC1 in regulating bone development by generating and characterizing an osteoblast-specific Tsc1 conditional knock-out (CKO) mouse model.
Methods: Tsc1F/F and Osterix-Cre+ mice were used to generate Tsc1F/F; Cre+ (CKO) and control (CTR) littermates. The latter includes both Tsc1+/+; Cre+ and Tsc1F/F mice.
Results: Tsc1 CKO mice were born at the expected Mendelian frequency, but with lighter body weight and shorter body length, compared with CTR littermates.
Immunohistochemistry (IHC) staining demonstrated that while both CTR and CKO femurs had similar S6 ribosomal protein levels, Tsc1-deficient femurs displayed a heightened protein expression of phospho-S6 ribosomal protein, indicating the enhanced activity of mTORC1 in the absence of osteoblastic TSC1.
Micro-computed tomography analyses demonstrated that Tsc1 CKO mice displayed a significantly reduced three dimensional trabecular bone volume fraction, thickness, and number, whereas they exhibited a significant increase in trabecular separation, compared with gender-matched Tsc1F/F littermates.
Consistently H&E stain showed Tsc1 CKO mice had reduced trabecular bone mass and disorganized cortical bones. In addition, they displayed enhanced bone marrow adiposity.
Further, qRT-PCR analysis showed that Tsc1-deficient bone tissues had reduced gene expression of osteoblastic markers, the results demonstrated that TSC1 deficiency leads to compromised osteoblastogenesis.
Since osteoblastic-specific TSC1 CKO mice exhibited reduced osteoblastogenesis and increased bone marrow adipogenesis, recapitulating bone phenotypes, in mice, caused by loss-of -function of Wnt/β-catenin signaling.
We further determined status of Wnt/β-catenin signaling in TSC1 deficient bone tissues in vivo. IHC staining demonstrated a drastic reduction of protein expression of β-catenin in TSC1 deficient mice. In contrast, TSC1 deficiency resulted in an increase in protein expression of sclerostin, a inhibitor for canonical Wnt signaling.
Conclusions: Our study demonstrated that an intact TSC1/mTOR signaling is required for normal bone development and proper bone marrow homeostasis.
Methods: Tsc1F/F and Osterix-Cre+ mice were used to generate Tsc1F/F; Cre+ (CKO) and control (CTR) littermates. The latter includes both Tsc1+/+; Cre+ and Tsc1F/F mice.
Results: Tsc1 CKO mice were born at the expected Mendelian frequency, but with lighter body weight and shorter body length, compared with CTR littermates.
Immunohistochemistry (IHC) staining demonstrated that while both CTR and CKO femurs had similar S6 ribosomal protein levels, Tsc1-deficient femurs displayed a heightened protein expression of phospho-S6 ribosomal protein, indicating the enhanced activity of mTORC1 in the absence of osteoblastic TSC1.
Micro-computed tomography analyses demonstrated that Tsc1 CKO mice displayed a significantly reduced three dimensional trabecular bone volume fraction, thickness, and number, whereas they exhibited a significant increase in trabecular separation, compared with gender-matched Tsc1F/F littermates.
Consistently H&E stain showed Tsc1 CKO mice had reduced trabecular bone mass and disorganized cortical bones. In addition, they displayed enhanced bone marrow adiposity.
Further, qRT-PCR analysis showed that Tsc1-deficient bone tissues had reduced gene expression of osteoblastic markers, the results demonstrated that TSC1 deficiency leads to compromised osteoblastogenesis.
Since osteoblastic-specific TSC1 CKO mice exhibited reduced osteoblastogenesis and increased bone marrow adipogenesis, recapitulating bone phenotypes, in mice, caused by loss-of -function of Wnt/β-catenin signaling.
We further determined status of Wnt/β-catenin signaling in TSC1 deficient bone tissues in vivo. IHC staining demonstrated a drastic reduction of protein expression of β-catenin in TSC1 deficient mice. In contrast, TSC1 deficiency resulted in an increase in protein expression of sclerostin, a inhibitor for canonical Wnt signaling.
Conclusions: Our study demonstrated that an intact TSC1/mTOR signaling is required for normal bone development and proper bone marrow homeostasis.