Substrate elasticity regulates vascular endothelial growth factor A (VEGFA) expression in adipose-derived stromal cells: Implications for potential angiogenesis

Matrix stiffness regulates the triad communication of adipocytes/macrophages/endothelial cells through CXCL13

Adipose tissue remodeling and plasticity are dynamically regulated by the coordinated functions of adipocytes, macrophages, and endothelial cells and extracellular matrix (ECM) that provides stiffness networks in adipose tissue component cells. Inflammation and fibrosis are crucial exogenous factors that dysregulate adipose tissue functions and drastically change the mechanical properties of the ECM. Therefore, communication among the ECM and adipose tissue component cells is necessary to understand the multifaceted functions of adipose tissues. To obtain in vivo stiffness, we utilized genipin as a crosslinker for collagen gels. Meanwhile, we isolated primary adipocytes, macrophages, and endothelial cells from C57BL/6J mice and incubated these cells in the differentiation media on temperature-responsive culture dishes. After the differentiation, these cell sheets were transferred onto genipin-crosslinked collagen gels with varying matrix stiffness. We found that inflammatory gene expressions were induced by hard matrix, whereas anti-inflammatory gene expressions were promoted by soft matrix in all three types of cells. Interestingly, the co-culture experiments of adipocytes, macrophages, and endothelial cells showed that the effects of soft or hard matrix stiffness stimulation on adipocytes were transmitted to the distant adipose tissue component cells, altering their gene expression profiles under normal matrix conditions. Finally, we identified that a hard matrix induces the secretion of CXCL13 from adipocytes, and CXCL13 is one of the important transmitters for stiffness communication with macrophages and endothelial cells. These findings provide insight into the mechano-transmission into distant cells and the application of stiffness control for chronic inflammation in adipose tissues with metabolic dysregulation.

Microenvironmental Stiffness Directs Chondrogenic Lineages of Stem Cells from the Human Apical Papilla via Cooperation between ROCK and Smad3 Signaling

Cell-based cartilage tissue engineering faces a great challenge in the repair process, partly due to the special physical microenvironment. Human stem cell from apical papilla (hSCAP) shows great potential as seed cells because of its versatile differentiation capacity. However, whether hSCAP has potent chondrogenic differentiation ability in the physical microenvironment of chondroid remains unknown. In this study, we fabricated poly(dimethylsiloxane) (PDMS) substrates with different stiffnesses and investigated the chondrogenic differentiation potential of hSCAPs. First, we found that hSCAPs cultured on soft substrates spread more narrowly accompanied by cortical actin organization, a hallmark of differentiated chondrocytes. On the contrary, stiff substrates were favorable for cell spreading and stress fiber formation. More importantly, the increased chondrogenic differentiation of hSCAPs seeded on soft substrates was confirmed by characterizing increased extracellular proteoglycan aggregation through Alcian blue staining and Safranin O staining and enhanced markers toward chondrogenic differentiation including SRY-box transcription factor 9 (Sox9), type II collagen (Col2), and aggrecan in both normal α-minimum essential medium (αMEM) and specific chondrogenic medium (CM) culture conditions. Then, we investigated the mechanosensing/mechanotransduction governing the chondrogenic differentiation of hSCAPs in response to different stiffnesses and found that stiffness-sensitive integrin β1 and focal adhesion kinase (FAK) were essential for mechanical signal perception and were oriented at the start of mechanotransduction induced by matrix stiffness. We next showed that the increased nuclear accumulation of Smad3 signaling and target Sox9 facilitated the chondrogenic differentiation of hSCAPs on the soft substrates and further verified the importance of Rho-associated protein kinase (ROCK) signaling in regulating chondrogenic differentiation and its driving factors, Smad3 and Sox9. By using SIS3, the specific inhibitor of p-Smad3, and miRNA targeting Rho-associated protein kinase 1 (ROCK-1), we finally confirmed the importance of ROCK/Smad3/Sox9 axis in the chondrogenic differentiation of hSCAPs in response to substrate stiffness. These results help us to increase the understanding of how microenvironmental stiffness directs chondrogenic differentiation from the aspects of mechanosensing, mechanotransduction, and cell fate decision, which will be of great value in the application of hSCAPs in cartilage tissue engineering.

TPTEP1 suppresses high glucose-induced dysfunction in retinal vascular endothelial cells by interacting with STAT3 and targeting VEGFA

AIMS

Diabetic retinopathy (DR) is a vascular complication of diabetes mellitus that causes visual impairment and blindness. Long noncoding RNAs (lncRNAs) have been revealed to be involved in biological processes of several diseases including DR. We designed this study to investigate the specific role of TPTEP1 in DR.

METHODS

First, we mimicked diabetic conditions with high glucose (HG) stimulation of human retinal vascular endothelial cells (HRVECs) and measured TPTEP1 expression in HG-stimulated HRVECs using RT-qPCR analysis. Then, CCK-8, Transwell, and Matrigel tube formation assays as well as western blot analysis were performed to reveal the biological functions of TPTEP1 in HG-stimulated HRVECs. Subsequently, bioinformatics analysis, RNA pull down, luciferase reporter and ChIP assays as well as western blot analysis evaluated the relationship of TPTEP1, signal transducer and activator of transcription 3 (STAT3) and vascular endothelial growth factor A (VEGFA) in HG-stimulated HRVECs. Finally, to verify the regulation of the TPTEP1/STAT3/VEGFA axis in HG-stimulated HRVECs, rescue experiments were carried out in HG-stimulated HRVECs.

RESULTS

TPTEP1 presented a significant downregulation in HG-stimulated HRVECs. Additionally, TPTEP1 overexpression reduced viability, migration, and angiogenesis in HG-stimulated HRVECs. Moreover, TPTEP1 suppressed phosphorylation and nuclear translocation of STAT3, and thereby downregulated VEGFA mRNA and protein levels. Furthermore, TPTEP1 overexpression-mediated suppression of HG-induced dysfunction in HRVECs was countervailed by STAT3 upregulation or VEGFA upregulation.

CONCLUSIONS

TPTEP1 alleviated HG-induced dysfunction in HRVECs via interacting with STAT3 and targeting VEGFA.

Biomaterial Stiffness Guides Cross-talk between Chondrocytes: Implications for a Novel Cellular Response in Cartilage Tissue Engineering

The exquisite cartilage architecture maintains an orderly dynamic equilibrium as a result of the interplay between chondrocyte functions and the unique extracellular matrix (ECM) microenvironment. Numerous studies have demonstrated that extracellular cues, including topological, mechanical, and biochemical properties of the underlying substrates, dictate the chondrocyte behaviors. Consequently, developing advanced biomaterials with the desired characteristics which could achieve the biointerface between cells and the surrounded matrix close to the physiological conditions becomes a great hotspot in bioengineering. However, how the substrate stiffness influences the intercellular communication among chondrocytes is still poorly reported. We used polydimethylsiloxane with varied stiffnesses as a cell culture substrate to elucidate a novel cell-to-cell communication in a collective of chondrocytes. First, morphological images collected using scanning electron microscopy revealed that the tunable substrate stiffnesses directed the changes in intercellular links among chondrocytes. Next, fibronectin, which played a vital role in the connection of ECM components or linkage of ECM to chondrocytes, was shown to be gathered along cell-cell contact areas and was changed with the tunable substrate stiffnesses. Furthermore, transmembrane junctional proteins including connexin 43 (Cx43) and pannexin 1 (Panx1), which are responsible for gap junction formation in cell-to-cell communication, were mediated by the tunable substrate stiffnesses. Finally, through a scrape loading/dye transfer assay, we revealed cell-to-cell communication changes in a living chondrocyte population in response to the tunable substrate stiffnesses via cell-to-cell fluorescent molecule transport. Taken together, this novel cell-to-cell communication regulated by biomaterial stiffness could help us to increase the understanding of cell behaviors under biomechanical control and may ultimately lead to refining cell-based cartilage tissue engineering.

Osteoporosis-decreased extracellular matrix stiffness impairs connexin 43-mediated gap junction intercellular communication in osteocytes

Osteocytes are the main sensitive and responsive cells for mechanical stimuli in bone. The connexin family enables them to communicate with each other via forming functional gap junctions. However, how osteoporosis-impaired extracellular mechanical property modulates gap junction intercellular communication in osteocytes remains elusive. In this study, we established an ovariectomy (OVX)-induced osteoporosis mouse model in vivo and a polydimethylsiloxane (PDMS)-based cell culture substrate model in vitro to explore the influence of extracellular matrix (ECM) stiffness on cell-to-cell communication in osteocytes. Firstly, we established an OVX-induced osteoporosis mouse model by characterizing the changes in radiography, morphology and histochemistry of femurs. Our results showed that osteoporosis decreased the bone matrix stiffness together with the changes including the loss of osteocytes and the decrease of protein markers. Meanwhile, the dendritic process interconnection and channel-forming protein, Cx43, were reduced in osteoporosis mice. Next we mimicked ECM stiffness changes in vitro by using PDMS substrates at ratios 1:5 for normal stiffness and 1:45 for osteoporosis stiffness. Our results showed that the decreased ECM stiffness reduced the number of dendritic processes in a single cell and gap junctions between adjacent osteocytes. We further detected the decreased expression of Cx43, in the substrate with decreased stiffness. Finally, we found that gap junction-based intercellular communication was reduced in living osteocytes in the substrate with decreased stiffness. This study demonstrates the correlation between ECM mechanical property and cell-to-cell communication in osteocytes and might pave the way for further exploration of osteoporosis in terms of biomechanics.

Substrate mechanics dictate cell-cell communication by gap junctions in stem cells from human apical papilla

It is recognized that the interaction between cells and their physical microenvironment plays a fundamental role in controlling cell behaviors and even in determining cell fate. Any change in the physical properties of the extracellular matrix (ECM), such as its topography, geometry, and stiffness, controls this interaction. In the current study, we revealed a potent interconnection between the cell-matrix interaction and cell-cell communication that is mediated by interface stiffness, and elucidated this process in stem cells from human apical papilla (hSCAPs) in terms of mechanosensing, mechanotransduction, and gap junction-mediated cell-cell communication. We first fabricated polydimethylsiloxane (PDMS) substrates with the same topography and geometry but different stiffnesses and found that the cell morphology of the hSCAPs actively changed to adapt to the difference in substrate stiffness. We also found that the hSCAPs secreted more fibronectin in response to the stiff substrate. The focal adhesion plaques were changed by altering the expression of focal adhesion kinase (FAK) and paxillin. The FAK and paxillin bound to connexin 43 and, as a result, altered the gap junction formation. By performing a Lucifer yellow transfer assay, we further confirmed that the interface stiffness mediated cell-cell communication in living hSCAPs through changes in gap junction tunnels. The intrinsic mechanism that mediated cell-cell communication by extracellular stiffness show the great influence of the interaction between cells and their external physical microenvironment and stress the importance of microenvironmental mechanics in organ development and diseases. STATEMENT OF SIGNIFICANCE: Biochemical factors could direct cell behaviors such as cell proliferation, migration, differentiation, cell cycling and apoptosis. Likewise, biophysical factors could also determine cell behaviors in all biological processes. In the current study, we revealed a potent interconnection between the cell-matrix interaction and cell-cell communication by elucidating the whole process from cell mechanosensing, mechanotransduction to gap junction-mediated cell-cell communication. This process occurs in a collective of cells but not in that of a single cell. Biophysical properties of ECM induced cell-to-cell communication indicates the importance of microenvironmental mechanics in organ development and diseases. These findings should be of great interest in all biological fields, especially in biomaterials - cell/molecular biology involved in the interactions between the cell and its matrix.

Stiffness and topography of biomaterials dictate cell-matrix interaction in musculoskeletal cells at the bio-interface: A concise progress review

Mutually interacted musculoskeletal tissues work together within the physiological environment full of varieties of external stimulus. Consistent with the locomotive function of the tissues, musculoskeletal cells are remarkably mechanosensitive to the physical cues. Signals like extracellular matrix (ECM) stiffness, topography, and geometry can be sensed and transduced into intracellular signaling cascades to trigger a series of cell responses, including cell adhesion, cell phenotype maintenance, cytoskeletal reconstruction, and stem cell differentiation (Du et al., 2011; Murphy et al., 2014; Lv et al., 2015; Kim et al., 2016; Kumar et al., 2017). With the development of tissue engineering and regenerative medicine, the potent effects of ECM physical properties on cell behaviors at the cell-matrix interface are drawing much attention. To mimic the interaction between cell and its ECM physical properties, developing advanced biomaterials with desired characteristics which could achieve the biointerface between cells and the surrounded matrix close to the physiological conditions becomes a great hotspot. In this review, based on the current publications in the field of biointerfaces, we systematically summarized the significant roles of stiffness and topography on musculoskeletal cell behaviors. We hope to shed light on the importance of physical cues in musculoskeletal tissue engineering and provide up to date strategies towards the natural or artificial replication of physiological microenvironment.

Insights into the angiogenic effects of nanomaterials: mechanisms involved and potential applications

The vascular system, which transports oxygen and nutrients, plays an important role in wound healing, cardiovascular disease treatment and bone tissue engineering. Angiogenesis is a complex and delicate regulatory process. Vascular cells, the extracellular matrix (ECM) and angiogenic factors are indispensable in the promotion of lumen formation and vascular maturation to support blood flow. However, the addition of growth factors or proteins involved in proangiogenic effects is not effective for regulating angiogenesis in different microenvironments. The construction of biomaterial scaffolds to achieve optimal growth conditions and earlier vascularization is undoubtedly one of the most important considerations and major challenges among engineering strategies. Nanomaterials have attracted much attention in biomedical applications due to their structure and unique photoelectric and catalytic properties. Nanomaterials not only serve as carriers that effectively deliver factors such as angiogenesis-related proteins and mRNA but also simulate the nano-topological structure of the primary ECM of blood vessels and stimulate the gene expression of angiogenic effects facilitating angiogenesis. Therefore, the introduction of nanomaterials to promote angiogenesis is a great helpful to the success of tissue regeneration and some ischaemic diseases. This review focuses on the angiogenic effects of nanoscaffolds in different types of tissue regeneration and discusses the influencing factors as well as possible related mechanisms of nanomaterials in endothelial neovascularization. It contributes novel insights into the design and development of novel nanomaterials for vascularization and therapeutic applications.