Mecp2 fine-tunes quiescence exit by targeting nuclear receptors.

Quiescence (G0) maintenance and exit are crucial for tissue homeostasis and regeneration in mammals. Here, we show that methyl-CpG binding protein 2 (Mecp2) expression is cell cycle-dependent and negatively regulates quiescence exit in cultured cells and in an injury-induced liver regeneration mouse model. Specifically, acute reduction of Mecp2 is required for efficient quiescence exit as deletion of Mecp2 accelerates, while overexpression of Mecp2 delays quiescence exit, and forced expression of Mecp2 after Mecp2 conditional knockout rescues cell cycle reentry. The E3 ligase Nedd4 mediates the ubiquitination and degradation of Mecp2, and thus facilitates quiescence exit. A genome-wide study uncovered the dual role of Mecp2 in preventing quiescence exit by transcriptionally activating metabolic genes while repressing proliferation-associated genes. Particularly disruption of two nuclear receptors, Rara or Nr1h3, accelerates quiescence exit, mimicking the Mecp2 depletion phenotype. Our studies unravel a previously unrecognized role for Mecp2 as an essential regulator of quiescence exit and tissue regeneration.

Bindarit Reduces Bone Loss in Ovariectomized Mice by Inhibiting CCL2 and CCL7 Expression via the NF-κB Signaling Pathway.

OBJECTIVE: To investigate the changes in proinflammatory cytokines and chemokines, namely, C-C motif ligand (CCL) 2 and CCL7, in postmenopausal osteoporosis (PMOP) and to develop a new drug, bindarit (Bnd), for PMOP in an ovariectomized (OVX) mouse model. METHODS: Bone marrow macrophages (BMMs) from the femurs of five women with PMOP and five premenopausal women without osteoporosis were detected by RNA sequencing. BMMs from mice were differentiated into osteoclasts and treated with a synthetic inhibitor of CCL2 and CCL7, Bnd, or 17 beta estradiol (E2 ). Mouse BMMs were differentiated into osteoclasts with or without Bnd for 7 days and analyzed by RNA sequencing. Osteoblasts of mice were induced to undergo osteoblastogenesis and treated with Bnd. OVX mice were treated with E2 or Bnd after surgery. The protein and mRNA expression of CCL2 and CCL7 was detected using immunostaining and qPCR, respectively, in OVX and aged mice and in cells cultured in vitro. Osteoclast formation was detected using a tartrate-resistant acid phosphatase (TRAP) assay in vitro and in vivo. Alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2) and osteocalcin (OCN) were detected using immunostaining to evaluate osteogenesis. Microcomputed tomography was conducted to analyze trabecular bone parameters, the structure model index, bone mineral density and other variables. Nuclear factor-κB (NF-κB) signaling pathway-related protein phosphorylation of IKKα/ß (p-IKKα/ß) and p-NFκB p65 was examined using western blotting. RESULTS: CCL2, CCL7 and their receptor of C-C chemokine receptor-2 (CCR2), and the NF-κB signaling pathway, were significantly increased in women with PMOP. CCL2 and CCL7 protein and mRNA expression was increased in OVX mice and aged female mice, but the increases were attenuated by E2 and Bnd. E2 and Bnd effectively inhibited osteoclastogenesis and the protein expression of CCL2 and CCL7 both in vitro and in vivo and reduced bone loss in OVX mice. Bnd did not affect the mineralization of osteoblasts directly in vitro but reduced bone turnover in vivo. p-IKKα/ß and p-NFκB p65 levels were increased in BMMs of mice after differentiation into osteoclasts but were significantly decreased by Bnd. CONCLUSION: The proinflammatory cytokines and chemokines CCL2, CCL7 and CCR2 were correlated with PMOP. Bnd attenuated the increases in CCL2 and CCL7 levels to affect osteoporosis in OVX mice via the NFκB signaling pathway. Thus, Bnd may be useful as a new therapeutic for the prevention of PMOP.

DEPTOR expression negatively correlates with mTORC1 activity and tumor progression in colorectal cancer.

The mammalian target of rapamycin (mTOR) signaling pathway is upregulated in the pathogenesis of many cancers, including colorectal cancer (CRC). DEPTOR is an mTOR inhibitor whose expression is negatively regulated by mTOR. However, the role of DEPTOR in the development of CRC is not known. The aim of this study was to investigate the expression of DEPTOR and mTORC1 activity (P-S6) in a subset of CRC patients and determine their relation to tumor differentiation, invasion, nodal metastasis and disease-free survival. Here, Immunohistochemical expression of P-S6 (S235/236) and DEPTOR were evaluated in 1.5 mm tumor cores from 90 CRC patients and in 90 samples of adjacent normal mucosa by tissue microarray. The expression of P-S6 (S235/236) was upregulated in CRC, with the positive rate of P-S6 (S235/236) in CRC (63.3%) significantly higher than that in control tissues (36.7%, 30%) (p<0.05). P-S6 (S235/236) also correlated with high tumor histologic grade (p=0.002), and positive nodal metastasis (p=0.002). In contrast, the expression level of DEPTOR was correlated with low tumor histological grade (p=0.006), and negative nodal metastasis (p=0.001). Interestingly, P-S6 (S235/236) expression showed a significant negative association with the expression of DEPTOR in CRC (p=0.011, R= -0.279). However, upregulation of P-S6 (S235/236) (p=0.693) and downregulation of DEPTOR (p=0.331) in CRC were not significantly associated with overall survival. Thus, we conclude that expression of DEPTOR negatively correlates with mTORC1 activity and tumor progression in CRC. DEPTOR is a potential marker for prognostic evaluation and a target for the treatment of CRC.

Endogenous n-3 polyunsaturated fatty acids (PUFAs) mitigate ovariectomy-induced bone loss by attenuating bone marrow adipogenesis in FAT1 transgenic mice.

AIM: To investigate the effect of endogenous n-3 polyunsaturated fatty acids (PUFAs) on bone marrow adipogenesis under osteoporosis conditions. METHODS: A mouse osteoporosis model overexpressing the FAT1 gene from Caenorhabditis elegans and converting n-6 PUFAs to n-3 PUFAs endogenously was used. RESULTS: The mice presented significantly lower bone marrow adiposity (adipocyte volume/tissue volume, mean adipocyte number) but increased the bone parameters (bone mineral density, bone mineral content, bone volume/total volume) in the distal femoral metaphysis. CONCLUSION: Endogenous n-3 PUFAs protect bone marrow adipogenesis, which provides a novel drug target.

Risedronate inhibits bone marrow mesenchymal stem cell adipogenesis and switches RANKL/OPG ratio to impair osteoclast differentiation.

BACKGROUND: Osteoporosis is accompanied by an increase in bone marrow adipose tissue. Bone marrow adipogenesis has emerged as a therapeutic target for prevention of bone loss. Amino-bisphosphonates have been widely used for treatment of osteoporosis, but the mechanism through which amino-bisphosphonates inhibit osteoporosis remains unclear. The purpose of this study is to investigate the effects of bisphosphonates on bone marrow adipogenesis and the pro-osteoclastic factors produced by adipocytes in bone marrow microenvironment. MATERIALS AND METHODS: Human mesenchymal stem cells were obtained and purified from six volunteer donors. Each sample of cells was treated by increasing concentrations of risedronate with or without adipogenic induction for 14 d, and then droplets of the differentiated adipocytes were analyzed. The level of receptor activator of nuclear factor-κB ligand and osteoprotegerin, as well as pro-osteoclastic inflammatory factors interleukin-1, interleukin-6, and tumor necrosis factor α produced by adipocytes were evaluated by Western blot and ELISA assay. Moreover, the effect of risedronate on the activity of mammalian target of rapamycin complex 1, a key Ser/Thr kinase for initiation of adipocyte differentiation, was investigated. RESULTS: Risedronate not only dose-dependently inhibited the bone marrow adipogenesis from human mesenchymal stem cells but also suppressed receptor activator of nuclear factor-κB ligand, not osteoprotegerin, expression in differentiated adipocytes, as well as pro-osteoclastic inflammatory factors. Furthermore, the activity of mammalian target of rapamycin complex 1 was suppressed by risedronate. CONCLUSION: Our findings that risedronate influences the crosstalk between bone marrow adipocyte-osteoclast represent a novel mechanism for the anti-osteoporotic effects of risedronate.