Conditional loss of IKKα in Osterix + cells has no effect on bone but leads to age-related loss of peripheral fat

AUTHORS

Jennifer L. Davis, Nitin Kumar Pokhrel, Linda Cox, Nidhi Rohatgi, Roberta Faccio & Deborah J. Veis

ABSTRACT

NF-κB has been reported to both promote and inhibit bone formation. To explore its role in osteolineage cells, we conditionally deleted IKKα, an upstream kinase required for non-canonical NF-κB activation, using Osterix (Osx)-Cre. Surprisingly, we found no effect on either cancellous or cortical bone, even following mechanical loading. However, we noted that IKKα conditional knockout (cKO) mice began to lose body weight after 6 months of age with severe reductions in fat mass and lower adipocyte size in geriatric animals. qPCR analysis of adipogenic markers in fat pads of cKO mice indicated no difference in early differentiation, but instead markedly lower leptin with age. We challenged young mice with a high fat diet finding that cKO mice gained less weight and showed improved glucose metabolism. Low levels of recombination at the IKKα locus were detected in fat pads isolated from old cKO mice. To determine whether recombination occurs in adipocytes, we examined fat pads in Osx-Cre;TdT reporter mice; these showed increasing Osx-Cre-mediated expression in peripheral adipocytes from 6 weeks to 18 months. Since Osx-Cre drives recombination in peripheral adipocytes with age, we conclude that fat loss in cKO mice is most likely caused by progressive deficits of IKKα in adipocytes

Skeletal muscle mitoribosomal defects are linked to low bone mass caused by bone marrow inflammation in male mice

AUTHORS

Jingwen Tian, Hyo Kyun Chung, Ji Sun Moon, Ha Thi Nga, Ho Yeop Lee, Jung Tae Kim, Joon Young Chang, Seul Gi Kang, Dongryeol Ryu, Xiangguo Che, Je-Yong Choi, Masayuki Tsukasaki, Takayoshi Sasako, Sang-Hee Lee, Minho Shong, Hyon-Seung Yi

ABSTRACT

Background

Mitochondrial oxidative phosphorylation (OxPhos) is a critical regulator of skeletal muscle mass and function. Although muscle atrophy due to mitochondrial dysfunction is closely associated with bone loss, the biological characteristics of the relationship between muscle and bone remain obscure. We showed that muscle atrophy caused by skeletal muscle-specific CR6-interacting factor 1 knockout (MKO) modulates the bone marrow (BM) inflammatory response, leading to low bone mass.

Methods

MKO mice with lower muscle OxPhos were fed a normal chow or high-fat diet and then evaluated for muscle mass and function, and bone mineral density. Immunophenotyping of BM immune cells was also performed. BM transcriptomic analysis was used to identify key factors regulating bone mass in MKO mice. To determine the effects of BM-derived CXCL12 (C–X–C motif chemokine ligand 12) on regulation of bone homeostasis, a variety of BM niche-resident cells were treated with recombinant CXCL12. Vastus lateralis muscle and BM immune cell samples from 14 patients with hip fracture were investigated to examine the association between muscle function and BM inflammation.

Results

MKO mice exhibited significant reductions in both muscle mass and expression of OxPhos subunits but increased transcription of mitochondrial stress response-related genes in the extensor digitorum longus (P < 0.01). MKO mice showed a decline in grip strength and a higher drop rate in the wire hanging test (P < 0.01). Micro-computed tomography and von Kossa staining revealed that MKO mice developed a low mass phenotype in cortical and trabecular bone (P < 0.01). Transcriptomic analysis of the BM revealed that mitochondrial stress responses in skeletal muscles induce an inflammatory response and adipogenesis in the BM and that the CXCL12–CXCR4 (C–X–C chemokine receptor 4) axis is important for T-cell homing to the BM. Antagonism of CXCR4 attenuated BM inflammation and increased bone mass in MKO mice. In humans, patients with low body mass index (BMI = 17.2 ± 0.42 kg/m2) harboured a larger population of proinflammatory and cytotoxic senescent T-cells in the BMI (P < 0.05) and showed reduced expression of OxPhos subunits in the vastus lateralis, compared with controls with a normal BMI (23.7 ± 0.88 kg/m2) (P < 0.01).

Conclusions

Defects in muscle mitochondrial OxPhos promote BM inflammation in mice, leading to decreased bone mass. Muscle mitochondrial dysfunction is linked to BM inflammatory cytokine secretion via the CXCL12–CXCR4 signalling axis, which is critical for inducing low bone mass.

Probabilistic model for cattail and canola fibers: effect of environmental conditions, structural parameters, fiber length, and estimators

AUTHORS

Md Shadhin, Danny Mann, Mashiur Rahman

ABSTRACT

Biomass fibers are being widely investigated for industrial applications as an alternative to synthetic fibers using a standard humidity condition. In this study, the mechanical properties of two waste biomass fibers – canola and cattail – have been investigated when subjected to different environmental conditions, fiber length, and type of estimators used during analysis. The effect of different environmental conditions and structural variations were investigated by measuring the tensile properties after exposing them to eight different relative humidity conditions using a fixed fiber length of 25 mm. Further investigation was conducted using fiber lengths of 25, 35 and 45 mm using the most conservative relative humidity condition. The data were analyzed by a Weibull distribution model using four different estimators. The results revealed that Weibull strength (σavg) and modulus (Eavg) closely followed experimental values for cattail and canola fibers. The different relative humidity conditions and fiber lengths resulted in different Weibull parameters with 11% relative humidity and the mean rank estimator predicted the most conservative tensile strength for both waste biomass fibers. The experimental and characteristic Weibull strength decreased when fiber gauge length increased from 25 to 45 mm. The tensile strength and modulus of both waste biomass fibers at 50% reliability lie within the range of average experimental values. However, these values are reduced to 155 MPa (strength) and 20 GPa (modulus) for cattail fiber at 90% reliability. The survival probability of the tensile strength and modulus were found to be the highest at 75% and 100% relative humidity for cattail and canola fibers, respectively.

TET2 regulates osteoclastogenesis by modulating autophagy in OVX-induced bone loss

AUTHORS

Chen Yang, Huaqiang Tao, Haifeng Zhang, Yu Xia, Jiaxiang Bai, Gaoran Ge, Wenming Li, Wei Zhang, Long Xiao, Yaozeng Xu, Zhirong Wang, Ye Gu,H uilin Yang, Yu Liu & Dechun Geng

ABSTRACT

Increased bone resorption by osteoclasts after estrogen deficiency is the main cause of postmenopausal osteoporosis. TET2 (tet methylcytosine dioxygenase 2) is a DNA demethylase that regulates cellular function and differentiation potential. Macroautophagy/autophagy maintains cellular homeostasis by recycling unnecessary and damaged organelles. This study revealed that TET2 promoted bone loss in oophorectomized (OVX) mice and that TET2 promoted osteoclast differentiation by regulating autophagy. Tet2 knockdown inhibited autophagy and osteoclast differentiation in vitro. Mechanistically, Tet2 knockdown increased BCL2 (B cell leukemia/lymphoma 2) expression and BCL2 exhibited increased binding to BECN1 and negatively regulated autophagy. Small interfering RNA specific to Bcl2 interfered with BCL2 expression in Tet2-knockdown bone marrow cells/precursors, partially reversing autophagy dysregulation and promoting osteoclast differentiation. Moreover, the LV-shTet2 lentivirus prevented bone loss in OVX mice. In summary, our findings provide evidence that TET2 promotes osteoclast differentiation by inhibiting BCL2 expression and positively regulating BECN1-dependent autophagy.

Inhibition of myeloid PD-L1 suppresses osteoclastogenesis and cancer bone metastasis

AUTHORS

Hao Zuo & Yihong Wan

ABSTRACT

Programmed death-ligand 1 (PD-L1) is predominantly expressed in the antigen-presenting cells (APCs) that are originated and are abundant in the bone marrow. The roles of PD-L1 in bone cell differentiation and cancer bone metastasis remain unclear. Here we show that PD-L1 antibody or PD-L1 conditional knockout in the hematopoietic or myeloid lineage suppresses osteoclast differentiation in vitro and in vivo. Bone metastases of breast cancer and melanoma are diminished by PD-L1 antibody or PD-L1 deletion in the myeloid lineage. Transcriptional profiling of bone marrow cells reveals that PD-L1 deletion in the myeloid cells upregulates immune-stimulatory genes, leading to increased macrophage M1 polarization, decreased M2 polarization, enhanced IFNγ signaling, and elevated T cell recruitment and activation. All these alterations result in heightened anti-tumor immunity in the cancer microenvironment. Our findings support PD-L1 antibody as a potent therapy for bone metastasis of breast cancer and melanoma by simultaneously suppressing osteoclast and enhancing immunity.

3D gel-printed porous magnesium scaffold coated with dibasic calcium phosphate dihydrate for bone repair in vivo

AUTHORS

Yuxuan Zhang, Tao Lin, Haoye Meng, Xueting Wang, Hong Peng, Guangbo Liu, Shuai Wei, Qiang Lu, Yu Wang, Aiyuan Wang, Wenjing Xu, Huiping Shao, Jiang Peng

ABSTRACT

Background

Objective: The treatment of bone defect has always been a difficult problem in orthopedic clinic. The search for alternative biodegradable implants is a hot topic. The development of biodegradable magnesium scaffolds for the treatment of bone defects has long been a goal of the public.

Methods

In this study, we proposed a porous magnesium scaffold prepared by 3D gel printing and surface modification with an additional calcium phosphate coating and use of its strength, degradability and slow degradation rate in a bone graft substitute material. The porous magnesium granular scaffold was prepared by 3D gel printing technology and modified by DCPD (Dibasic Calcium Phosphate Dihydrate) coating. The biocompatibility, degradation rate, and osteogenic ability of the scaffold were evaluated in vitro and in vivo.

Results

The biocompatibility, in vivo degradation and bone defect healing response of the implants were investigated. Porous magnesium scaffolds were successfully prepared, and the strength of sintered scaffolds reached 5.38 ​MPa. The degradation rates of scaffolds were significantly reduced after coating with DCPD. The cell compatibility evaluation showed that DCPD-coated Mg scaffold was suitable for cell proliferation. In vivo biosafety monitoring showed that scaffold implantation did not cause an increase in Mg ion concentration in vivo, and no toxic damage was detected in the liver or kidney. Micro-CT and pathological results showed that a large amount of new bone was formed at 6 weeks. At 12 weeks, approximately 52% of the scaffold volume remained. At 24 weeks, osteogenesis, which was stimulated by some residual scaffold, still can be observed. In summary, this study suggests that 3D gel-printed DCPD-coated porous magnesium scaffolds have great potential as bone graft alternatives.

Conclusion

In summary, this study suggests that 3D gel-printed DCPD-coated porous magnesium scaffolds have great potential as bone graft alternatives.

The Translational potential of this article

The translational potential of this article is to make use of the advantages of 3D gel printing technology with higher efficiency and lower cost compared with SLM and SLS technologies, and use pure magnesium powder as raw material to prepare degradable porous magnesium metal scaffolds, opening up a new technical route for the preparation of degradable porous magnesium scaffolds which are made for bone defect regeneration in the future.