Dexamethasone-induced adipogenesis in primary marrow stromal cell cultures: mechanism of steroid-induced osteonecrosis.

BACKGROUND: In steroid-induced osteonecrosis, hypertrophy and hyperplasia of marrow fat cells and lipid deposition of osteocytes can be found in the femoral head. However, the precise reason is not clear yet. The aim of this study was to observe the effect of dexamethasone (Dex) on differentiation of marrow stromal cells (MSCs), and to investigate the pathobiological mechanism of steroid-induced osteonecrosis. METHODS: MSCs in cultures were treated with increasing concentrations of Dex (0, 10(-9), 10(-8), 10(-7), and 10(-6) mol/L) continuously for 21 days. The cells, which were exposed to 0 mol/L (control) or 10(-7) mol/L Dex for 4 - 21 days, were then cultured for 21 days without Dex. MSCs were stained with Sudan III. Number of adipocytes was counted under a light microscope. The activity of alkaline phosphatase (ALP) of MSCs treated with 0, 10(-8), 10(-7), and 10(-6) mol/L Dex for 12 days, and that treated with 0 mol/L and 10(-7) mol/L Dex for 8, 10, or 12 days were determined. The levels of triglycerides, osteocalcin and cell proliferation of MSCs treated with 0 mol/L and 10(-7) mol/L Dex were detected. The mRNA expression levels of adipose-specific 422 (aP2) gene and osteogenic gene type I collagen in MSCs treated with 0 mol/L and 10(-7) mol/L Dex for 6 days were analyzed by whole-cell dot-blot hybridization. Statistical analysis was performed using Student's t test and analysis of variance. P values less than 0.05 were considered significant statistically. RESULTS: The number of adipocytes in cultures increased with the duration of MSCs' exposure to Dex and the concentration of Dex. The level of ALP activity in the MSCs decreased with concentration of Dex. In the control group, it was 8.69 times of that in the 10(-7) mol/L Dex group on day 12 (t = 20.51, P < 0.001). The level of triglycerides in 10(-7) mol/L Dex group was 3.40 times of that in the control (t = 11.00, P < 0.001). The levels of cell proliferation and osteocalcin in the control were 1.54 and 2.42 times of that in the 10(-7) mol/L Dex group respectively. As compared to the control, the mRNA expression of adipose-specific 422 (aP2) gene in 10(-7) mol/L Dex group was significantly increased (t = 36.48, P < 0.001), and that of osteogenic gene type I collagen was decreased (t = 42.07, P < 0.001). CONCLUSIONS: Dex can directly induce the differentiation of MSCs into a large number of adipocytes and inhibit their osteogenic differentiation, which provide a novel explanation for the pathologic changes of steroid-induced osteonecrosis.

Construction and identification of the recombinant adenovirus vector carrying a small interfering RNA targeting the peroxisome proliferator-activated receptor-γ.

BACKGROUND: Steroid-induced osteonecrosis of the femoral head (ONFH) is a common clinical disease, with a high disability rate. At present, efficient prevention and treatment of steroid-induced ONFH is still lacking. The peroxisome proliferator-activated receptor-γ (PPARγ) is recognized as an important pathogenic gene for the development of steroid-induced ONFH. RNA interference (RNAi) is a tool for functional gene analysis, which has been successfully used to down-regulate the levels of specific target proteins. Therefore, down-regulation of PPARγ expression by RNAi may prevent the incidence of steroid-induced ONFH. METHODS: According to the principles of siRNA design, three duplex siRNA sequences (971 - 989, 1253 - 1271 and 1367 - 1385) derived from the PPARγ gene (NM_001082148) were synthesized. These duplexes were annealed, purified and ligated into 1.0-cytomegalovirus (CMV) shuttle vector. The shuttle vector was transfected into HEK293 cells. The HEK293 generated recombinant adenovirus vector carrying PPARγ siRNA sequences was purified and the titer of recombinant adenovirus was determined. RESULTS: After the annealing of single-strand DNA oligo encoding short hairpin RNA (shRNA) sequences, products were identified by gel electrophoresis. These products were ligated into the 1.0-CMV shuttle vector and the recombinant shuttle vectors 1.0-CMV-971, 1.0-CMV-1253 and 1.0-CMV-1367 were constructed. These sequences of these recombinant vectors were confirmed. We then successfully constructed the recombinant adenovirus vector carrying siRNA targeting PPARγ. After purification, the virus titer was higher than 10(10) plaque forming unit (PFU)/ml. CONCLUSION: In this study, three recombinant adenovirus shuttle vectors carrying siRNA targeting PPARγ, including shuttle vectors 1.0-CMV-971, 1.0-CMV-1253 and 1.0-CMV-1367, were successfully constructed and high titers of recombinant adenovirus were obtained.

Improvement of myocardial lipid accumulation and prevention of PGC-1α induction by fenofibrate.

We recently demonstrated that fenofibrate induces the activities of citrate synthase and NADH oxidase in cardiac mitochondria. To further determine the molecular mechanisms underlying fenofibrate action, 8-week-old mice were administered fenofibrate (100 mg/kg/day) for 7 and 14 days, and the expression of genes involved in cardiac mitochondrial function, such as nuclear respiratory factor 1 transcript variant 2 (NRF-1-L) and 6 (NRF-1-S), mitochondrial outer membrane protein 40 (Tom40), lipoic acid synthetase (Lias), cytochrome b, medium-chain acyl-coenzyme A dehydrogenase (MCAD) and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) was determined. Expression of PGC-1α, a key regulator of the entire fatty acid oxidation system, was significantly downregulated after 14 days of fenofibrate administration. Moreover, ventricular triglycerides were also accumulated following 14 days of fenofibrate administration. Thus, fenofibrate functions to improve myocardial lipid accumulation and to prevent PGC-1α induction, which is crucial for understanding the molecular mechanisms underlying fenofibrate action on the heart.

Osteogenic potential of human calcitonin gene-related peptide alpha gene-modified bone marrow mesenchymal stem cells.

BACKGROUND: Most of the basic and clinical studies of osteonecrosis of the femoral head (ONFH) are restricted to bone tissues only, whereas various systems are involved in the onset and development of ONFH, including nervous system. Peptidergic nerve participates in the neuronal regulation of bone metabolism and anabolism, and plays key roles in the growth, repair and reconstruction of bone. Calcitonin gene-related peptide (CGRP), which is secreted by peptidergic nerve, is the main mediator of bone metabolism. It dramatically promotes the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Additionally, it enhances the osteoblast mass and the rate of osteoblast formation, and reduces the bone resorption by acting on osteoblasts and osteoclasts. Hence, we aimed to construct recombinant retrovirus vector pLNCX(2)-hCGRPα and to investigate the proliferation and osteogenic potential of hCGRPα-producing BMSCs (BMSCs/pLNCX(2)-hCGRPα) after virus infection. METHODS: The constructed recombinant retrovirus vector pLNCX(2)-hCGRPα was transfected into PT67 packaging cells by lipofectamine 2000. Virus was collected for BMSCs infection. The mRNA and protein expression of hCGRPα was examined by reverse transcription polymerase chain reaction (RT-PCR) and Western blotting, respectively. The cell proliferation was determined by methyl thiazoleterazolium (MTT) assay. The osteogenic potential of BMSCs was evaluated by alkaline phosphatase (ALP) activity. RESULTS: Both mRNA and protein expression of hCGRPα was detected in BMSCs/pLNCX(2)-hCGRPα cells. These cells exhibited significantly elevated proliferation and ALP value as compared with control BMSCs (P < 0.05). CONCLUSION: BMSCs/pLNCX(2)-hCGRPα cells could stably express hCGRPα and showed promoted proliferation ability and osteogenic potential as compared with control BMSCs.