TGF-Beta Signaling in Bone with Chronic Kidney Disease

Bone repair and key signalling pathways for cell-based bone regenerative therapy: A review

Advances in cell-based regenerative therapy create new opportunities for the treatment of bone-related disorders and injuries, by improving the reparative phase of bone healing. Apart from the classical approach of bone grafting, the application of cell-based therapies, particularly stem cells (SCs), has gained a lot of attention in recent years. SCs play an important role in regenerative therapy due to their excellent ability to differentiate into bone-forming cells. Regeneration of new bone is regulated by a wide variety of signalling molecules and intracellular networks, which are responsible for coordinating cellular processes. The activated signalling cascade is significantly involved in cell survival, proliferation, apoptosis, and interaction with the microenvironment and other types of cells within the healing site. Despite the increasing evidence from studies conducted on signalling pathways associated with bone formation, the exact mechanism involved in controlling the differentiation stage of transplanted cells is not well understood. Identifying the key activated pathways involved in bone regeneration may allow for precise manipulation of the relevant signalling molecules within the progenitor cell population to accelerate the healing process. The in-depth knowledge of molecular mechanisms would be advantageous in improving the efficiency of personalised medicine and targeted therapy in regenerative medicine. In this review, we briefly introduce the theory of bone repair mechanism and bone tissue engineering followed by an overview of relevant signalling pathways that have been identified to play an important role in cell-based bone regenerative therapy.

Accelerated Bone Loss in Transgenic Mice Expressing Constitutively Active TGF-β Receptor Type I

Transforming growth factor beta (TGF-β) is a key factor mediating the intercellular crosstalk between the hematopoietic stem cells and their microenvironment. Here, we investigated the skeletal phenotype of transgenic mice expressing constitutively active TGF-β receptor type I under the control of Mx1-Cre (Mx1;TβRI^CA mice). μCT analysis showed decreased cortical thickness, and cancellous bone volume in both femurs and mandibles. Histomorphometric analysis confirmed a decrease in cancellous bone volume due to increased osteoclast number and decreased osteoblast number. Primary osteoblasts showed decreased ALP and mineralization. Constitutive TβRI activation increased osteoclast differentiation. qPCR analysis showed that Tnfsf11/Tnfrsf11b ratio, Ctsk, Sufu, and Csf1 were increased whereas Runx2, Ptch1, and Ptch2 were decreased in Mx1;TβRI^CA femurs. Interestingly, Gli1, Wnt3a, Sp7, Alpl, Ptch1, Ptch2, and Shh mRNA expression were reduced whereas Tnfsf11/Tnfrsf11b ratio was increased in Mx1;TβRI^CA mandibles. Similarly, osteoclast-related genes were increased in Mx1;TβRI^CA osteoclasts whereas osteoblast-related genes were reduced in Mx1;TβRI^CA osteoblasts. Western blot analysis indicated that SMAD2 and SMAD3 phosphorylation was increased in Mx1;TβRI^CA osteoblasts, and SMAD3 phosphorylation was increased in Mx1;TβRI^CA osteoclasts. CTSK was increased while RUNX2 and PTCH1 was decreased in Mx1;TβRI^CA mice. Microindentation analysis indicated decreased hardness in Mx1;TβRI^CA mice. Our study indicated that Mx1;TβRI^CA mice were osteopenic by increasing osteoclast number and decreasing osteoblast number, possibly by suppressing Hedgehog signaling pathways.

Role of MOTS-c in the regulation of bone metabolism

MOTS-c, a mitochondrial-derived peptide (MDP), is an essential regulatory mediator of cell protection and energy metabolism and is involved in the development of specific diseases. Recent studies have revealed that MOTS-c promotes osteoblast proliferation, differentiation, and mineralization. Furthermore, it inhibits osteoclast production and mediates the regulation of bone metabolism and bone remodeling. Exercise effectively upregulates the expression of MOTS-c, but the specific mechanism of MOTS-c regulation in bone by exercise remains unclear. Therefore, this article reviewed the distribution and function of MOTS-c in the tissue, discussed the latest research developments in the regulation of osteoblasts and osteoclasts, and proposed potential molecular mechanisms for the effect of exercise on the regulation of bone metabolism. This review provides a theoretical reference for establishing methods to prevent and treat skeletal metabolic diseases.

Strategies of Macrophages to Maintain Bone Homeostasis and Promote Bone Repair: A Narrative Review

Bone homeostasis (a healthy bone mass) is regulated by maintaining a delicate balance between bone resorption and bone formation. The regulation of physiological bone remodeling by a complex system that involves multiple cells in the skeleton is closely related to bone homeostasis. Loss of bone mass or repair of bone is always accompanied by changes in bone homeostasis. However, due to the complexity of bone homeostasis, we are currently unable to identify all the mechanisms that affect bone homeostasis. To date, bone macrophages have been considered a third cellular component in addition to osteogenic spectrum cells and osteoclasts. As confirmed by co-culture models or in vivo experiments, polarized or unpolarized macrophages interact with multiple components within the bone to ensure bone homeostasis. Different macrophage phenotypes are prone to resorption and formation of bone differently. This review comprehensively summarizes the mechanisms by which macrophages regulate bone homeostasis and concludes that macrophages can control bone homeostasis from osteoclasts, mesenchymal cells, osteoblasts, osteocytes, and the blood/vasculature system. The elaboration of these mechanisms in this narrative review facilitates the development of macrophage-based strategies for the treatment of bone metabolic diseases and bone defects.

Data Mining and Network Pharmacology Analysis of Kidney-Tonifying Herbs on the Treatment of Renal Osteodystrophy Based on the Theory of "Kidney Governing Bones" in Traditional Chinese Medicine

Background

Renal osteodystrophy (ROD) secondary to chronic kidney disease is closely associated with osteoporosis and fractures. Based on the theory of “kidney governing bones” in traditional Chinese medicine (TCM), treating bone diseases from the perspective of the kidney has become a basic principle of treating ROD. However, there are many kidney-tonifying herbs and their mechanisms of treating ROD are not clear. Therefore, our study intends to use data mining and network pharmacology to study the commonly used kidney-tonifying herbs, as well as their active ingredients and mechanisms of treating ROD.

Methods

We established a clinical ROD database by searching PubMed, CNKI, and other databases and screened out a core herbal combination of treating ROD. Furthermore, by using databases such as Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform and GeneCards, we obtained active ingredients and targets of the core herbal combination and ROD targets. The STRING website and Cytoscape software were then used to obtain information on key active ingredients and key targets. Finally, we conducted GO and KEGG analyses using the Metascape website and molecular docking using the AutoDock Vina software.

Results

Our study eventually included 58 prescriptions and 116 herbs of treating ROD. Through data mining, we found that yin-yang-huo, du-zhong, and bu-gu-zhi (YDB) constituted a core herbal combination to treat ROD. Network pharmacology showed that YDB mainly acted on targets such as estrogen receptor alpha through active ingredients such as quercetin by mitogen-activated protein kinase and other signaling pathways.

Conclusion

Many ingredients, targets, and pathways are involved in the treatment of YDB for ROD. Specifically, the flavonoids contained in YDB have great potential for ROD treatment.

Physical Training Inhibits the Fibrosis Formation in Alzheimer's Disease Kidney Influencing the TGFβ Signaling Pathways

Background:

Alzheimer’s disease (AD) is a neurodegenerative illness, with several peripheral pathological signs such as accumulation of amyloid-β (Aβ) plaques in the kidney. Alterations of transforming growth factor β (TGFβ) signaling in the kidney can induce fibrosis, thus disturbing the elimination of Aβ.

Objective:

A protective role of increased physical activity has been proven in AD and in kidney fibrosis, but it is not clear whether TGFβ signalization is involved in this effect.

Methods:

The effects of long-term training on fibrosis were investigated in the kidneys of mice representing a model of AD (B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J) by comparing wild type and AD organs. Alterations of canonical and non-canonical TGFβ signaling pathways were followed with PCR, western blot, and immunohistochemistry.

Results:

Accumulation of collagen type I and interstitial fibrosis were reduced in kidneys of AD mice after long-term training. AD induced the activation of canonical and non-canonical TGFβ pathways in non-trained mice, while expression levels of signal molecules of both TGFβ pathways became normalized in trained AD mice. Decreased amounts of phosphoproteins with molecular weight corresponding to that of tau and the cleaved C-terminal of AβPP were detected upon exercising, along with a significant increase of PP2A catalytic subunit expression.

Conclusion:

Our data suggest that physical training has beneficial effects on fibrosis formation in kidneys of AD mice and TGFβ signaling plays a role in this phenomenon.

Farnesoid X receptor activation inhibits TGFBR1/TAK1-mediated vascular inflammation and calcification via miR-135a-5p

Chronic inflammation plays a crucial role in vascular calcification. However, only a few studies have revealed the mechanisms underlying the development of inflammation under high-phosphate conditions in chronic kidney disease (CKD) patients. Here, we show that inflammation resulting from the activation of the TGFBR1/TAK1 pathway is involved in calcification in CKD rats or osteogenic medium-cultured human aortic smooth muscle cells (HASMCs). Moreover, miR-135a-5p is demonstrated to be a key regulator of the TGFBR1/TAK1 pathway, which has been reported to be decreased in CKD rats. We further reveal that farnesoid X receptor (FXR) activation increases miR-135a-5p expression, thereby inhibiting the activation of the TGFBR1/TAK1 pathway, ultimately resulting in the attenuation of vascular inflammation and calcification in CKD rats. Our findings provide advanced insights into the mechanisms underlying the development of inflammation in vascular calcification, and evidence that FXR activation could serve as a therapeutic strategy for retarding vascular calcification in CKD patients.

Human periodontal ligament stem cells on calcium phosphate scaffold delivering platelet lysate to enhance bone regeneration

Human periodontal ligament stem cells (hPDLSCs) are promising for tissue engineering applications but have received relatively little attention. Human platelet lysate (HPL) contains a cocktail of growth factors. To date, there has been no report on hPDLSC seeding on scaffolds loaded with HPL. The objectives of this study were to develop a calcium phosphate cement (CPC)-chitosan scaffold loaded with HPL and investigate their effects on hPDLSC viability, osteogenic differentiation and bone mineral synthesis for the first time. hPDLSCs were harvested from extracted human teeth. Scaffolds were formed by mixing CPC powder with a chitosan solution containing HPL. Four groups were tested: CPC-chitosan + 0% HPL (control); CPC-chitosan + 2.66% HPL; CPC-chitosan + 5.31% HPL; CPC-chitosan + 10.63% HPL. Scanning electron microscopy, live/dead staining, CCK-8, qRT-PCR, alkaline phosphatase and bone minerals assay were applied for hPDLSCs on scaffolds. hPDLSCs attached well on CPC-chitosan scaffold. Adding 10.63% HPL into CPC increased cell proliferation and viability (p < 0.05). ALP gene expression of CPC-chitosan + 10.63% HPL was 7-fold that of 0% HPL at 14 days. Runx2, OSX and Coll1 of CPC-chitosan + 10.63% HPL was 2-3 folds those at 0% HPL (p < 0.05). ALP activity of CPC-chitosan + 10.63% HPL was 2-fold that at 0% HPL (p < 0.05). Bone minerals synthesized by hPDLSCs for CPC-chitosan + 10.63% HPL was 3-fold that at 0% HPL (p < 0.05). This study showed that CPC-chitosan scaffold was a promising carrier for HPL delivery, and HPL in CPC exerted excellent promoting effects on hPDLSCs for bone tissue engineering for the first time. The novel hPDLSC-CPC-chitosan-HPL construct has great potential for orthopedic, dental and maxillofacial regenerative applications.

Inhibition of vascular smooth muscle cell calcification by vasorin through interference with TGFβ1 signaling

Elevated transforming growth factor β1 (TGFβ1) levels are frequently observed in chronic kidney disease (CKD) patients. TGFβ1 contributes to development of medial vascular calcification during hyperphosphatemia, a pathological process promoted by osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells (VSMCs). Vasorin is a transmembrane glycoprotein highly expressed in VSMCs, which is able to bind TGFβ to inhibit TGFβ signaling. Thus, the present study explored the effects of vasorin on osteo-/chondrogenic transdifferentiation and calcification of VSMCs. Primary human aortic smooth muscle cells (HAoSMCs) were treated with recombinant human TGFβ1 or β-glycerophosphate without or with recombinant human vasorin or vasorin gene silencing by siRNA. As a result, TGFβ1 down-regulated vasorin mRNA expression in HAoSMCs. Vasorin supplementation inhibited TGFβ1-induced pathway activation, SMAD2 phosphorylation and downstream target genes expression in HAoSMCs. Furthermore, treatment with exogenous vasorin blunted, while vasorin knockdown augmented TGFβ1-induced osteo-/chondrogenic transdifferentiation of HAoSMCs. In addition, phosphate down-regulated vasorin mRNA expression in HAoSMCs. Phosphate-induced TGFβ1 expression was not affected by addition of exogenous vasorin. Nonetheless, the phosphate-induced TGFβ1 signaling, osteo-/chondrogenic transdifferentiation and calcification of HAoSMCs were all blunted by vasorin. Conversely, silencing of vasorin aggravated osteoinduction in HAoSMCs during high phosphate conditions. Aortic vasorin expression was reduced in the hyperphosphatemic klotho-hypomorphic mouse model of CKD-related vascular calcification. In conclusion, vasorin, which suppresses TGFβ1 signaling and protects against osteo-/chondrogenic transdifferentiation and calcification of VSMCs, is reduced by pro-calcifying conditions. Thus, vasorin is a novel key regulator of VSMC calcification and may represent a potential therapeutic target for vascular calcification during CKD.