Discoidin domain receptor 2 is an important modulator of BMP signaling during heterotopic bone formation

Bone morphogenetic proteins are essential for bone regeneration/fracture healing but can also induce heterotopic ossification (HO). Understanding accessory factors modulating BMP signaling would provide both a means of enhancing BMP-dependent regeneration while preventing HO. This study focuses on the ability of the collagen receptor, discoidin domain receptor 2 (DDR2), to regulate BMP activity. As will be shown, induction of bone formation by subcutaneous BMP2 implants is severely compromised in Ddr2-deficient mice. In addition, Ddr2 deficiency attenuates HO in mice expressing the ACVR1 mutation associated with human fibrodysplasia ossificans progressiva. In cells migrating into BMP2 implants, DDR2 is co-expressed with GLI1, a skeletal stem cell marker, and DDR2/GLI1-positive cells participate in BMP2-induced bone formation where they contribute to chondrogenic and osteogenic lineages. Consistent with this distribution, conditional knockout of Ddr2 in Gli1-expressing cells inhibited bone formation to the same extent seen in globally Ddr2-deficient animals. This response was explained by selective inhibition of Gli1+ cell proliferation without changes in apoptosis. The basis for this DDR2 requirement was explored further using bone marrow stromal cells. Although Ddr2 deficiency inhibited BMP2-dependent chondrocyte and osteoblast differentiation and in vivo, bone formation, early BMP responses including SMAD phosphorylation remained largely intact. Instead, Ddr2 deficiency reduced the nuclear/cytoplasmic ratio of the Hippo pathway intermediates, YAP and TAZ. This suggests that DDR2 regulates Hippo pathway-mediated responses to the collagen matrix, which subsequently affect BMP responsiveness. In summary, DDR2 is an important modulator of BMP signaling and a potential therapeutic target both for enhancing regeneration and treating HO.

Crucial roles of asprosin in cisplatin-induced ferroptosis and acute kidney injury

Ferroptosis is a type of non-apoptotic regulated cell death characterized by iron accumulation and lipid peroxidation. Cisplatin is an effective chemotherapy drug with several serious side effects including acute kidney injury (AKI). Asprosin is a peptide contributing to metabolism regulation and metabolic disorders. This study aimed to determine the role and mechanism of asprosin in AKI. Cisplatin was used to induce cell damage in mouse renal tubular epithelial (TCMK-1) cells and AKI in C57BL/6 mice. Cisplatin caused asprosin upregulation in cisplatin-treated TCMK-1 cells and mice. In TCMK-1 cells, asprosin overexpression led to iron overload and lipid peroxidation, while asprosin knockdown attenuated cisplatin-induced iron overload, lipid peroxidation and ferroptosis. Exogenous asprosin promoted cell damage and ferroptosis, which were attenuated by ferroptosis inhibitors. Asprosin-induced iron overload, lipid peroxidation, cell damage and SMAD1/5/8 phosphorylation were prevented by bone morphogenetic protein (BMP) type I receptor inhibitor. Integrin antagonist prevented asprosin-induced SMAD1/5/8 phosphorylation, and asprosin can specifically bind to integrin β3. Inhibition of integrin β3 reduced the asprosin-induced increases in Fe2+ and MDA levels. Asprosin knockdown relieved cisplatin-induced hepcidin upregulation, while hepcidin knockdown attenuated asprosin-induced iron overload, lipid peroxidation and ferroptosis. In cisplatin-induced AKI mice, specific knockdown of asprosin in the kidney not only attenuated renal dysfunction and damage, but also alleviated iron overload, lipid peroxidation and ferroptosis. These results indicated that excessively increased asprosin promotes TCMK-1 cells ferroptosis and damage via integrin β3/BMP/hepcidin-mediated iron overload and lipid peroxidation. Silencing of asprosin attenuates renal injury and dysfunction in cisplatin-induced AKI by inhibiting ferroptosis.

Characterization and preparation of food-derived peptides on improving osteoporosis: A review

Osteoporosis is a systemic bone disease characterized by reduced bone mass and deterioration of the microstructure of bone tissue, leading to an increased risk of fragility fractures and affecting human health worldwide. Food-derived peptides are widely used in functional foods due to their low toxicity, ease of digestion and absorption, and potential to improve osteoporosis. This review summarized and discussed methods of diagnosing osteoporosis, treatment approaches, specific peptides as alternatives to conventional drugs, and the laboratory preparation and identification methods of peptides. It was found that peptides interacting with RGD (arginine-glycine-aspartic acid)-binding active sites in integrin could alleviate osteoporosis, analyzed the interaction sites between these osteogenic peptides and integrin, and further discussed their effects on improving osteoporosis. These may provide new insights for rapid screening of osteogenic peptides, and provide a theoretical basis for their application in bone materials and functional foods.

Mechanical heterogeneity in a soft biomaterial niche controls BMP2 signaling

The extracellular matrix is known to impact cell function during regeneration by modulating growth factor signaling. However, how the mechanical properties and structure of biomaterials can be used to optimize the cellular response to growth factors is widely neglected. Here, we engineered a macroporous biomaterial to study cellular signaling in environments that mimic the mechanical stiffness but also the mechanical heterogeneity of native extracellular matrix. We found that the mechanical interaction of cells with the heterogeneous and non-linear deformation properties of soft matrices (E < 5 kPa) enhances BMP-2 growth factor signaling with high relevance for tissue regeneration. In contrast, this effect is absent in homogeneous hydrogels that are often used to study cell responses to mechanical cues. Live cell imaging and in silico finite element modeling further revealed that a subpopulation of highly active, fast migrating cells is responsible for most of the material deformation, while a second, less active population experiences this deformation as an extrinsic mechanical stimulation. At an overall low cell density, the active cell population dominates the process, suggesting that it plays a particularly important role in early tissue healing scenarios where cells invade tissue defects or implanted biomaterials. Taken together, our findings demonstrate that the mechanical heterogeneity of the natural extracellular matrix environment plays an important role in triggering regeneration by endogenously acting growth factors. This suggests the inclusion of such mechanical complexity as a design parameter in future biomaterials, in addition to established parameters such as mechanical stiffness and stress relaxation.

The transcription factor HIF-1α in NKp46+ ILCs limits chronic intestinal inflammation and fibrosis

Innate lymphoid cells (ILCs) are critical for intestinal adaptation to microenvironmental challenges, and the gut mucosa is characterized by low oxygen. Adaptation to low oxygen is mediated by hypoxia-inducible transcription factors (HIFs), and the HIF-1α subunit shapes an ILC phenotype upon acute colitis that contributes to intestinal damage. However, the impact of HIF signaling in NKp46+ ILCs in the context of repetitive mucosal damage and chronic inflammation, as it typically occurs during inflammatory bowel disease, is unknown. In chronic colitis, mice lacking the HIF-1α isoform in NKp46+ ILCs show a decrease in NKp46+ ILC1s but a concomitant rise in neutrophils and Ly6Chigh macrophages. Single-nucleus RNA sequencing suggests enhanced interaction of mesenchymal cells with other cell compartments in the colon of HIF-1α KO mice and a loss of mucus-producing enterocytes and intestinal stem cells. This was, furthermore, associated with increased bone morphogenetic pathway-integrin signaling, expansion of fibroblast subsets, and intestinal fibrosis. In summary, this suggests that HIF-1α-mediated ILC1 activation, although detrimental upon acute colitis, protects against excessive inflammation and fibrosis during chronic intestinal damage.

TGF-β1 promotes osteogenesis of mesenchymal stem cells via integrin mediated mechanical positive autoregulation

Positive autoregulation (PAR), one type of network motifs, provides a high phenotypic heterogeneity for cells to better adapt to their microenvironments. Typical mechanosensitive proteins can also form PAR, e.g., integrin mediated PAR, but the role of such mechanical PAR in physiological development and pathological process remains elusive. In this study, we found that transforming growth factor β1 (TGF-β1) and integrin levels decrease with tissue softening after the development of paradentium in vivo in rat model of periodontitis (an inflammatory disease with bone defect). Interestingly, TGF-β1 could induce the formation of mechanical PAR involving the integrin-FAK-YAP axis in mesenchymal stem cells (MSCs) by both in vitro experiments and in silico computational model. The computational model predicted a mechanical PAR involving the bimodal distribution of focus adhesions, which enables cells to accurately perceive extracellular mechanical cues. Thus, our analysis of TGF-β1 mediated mechanosensing mechanism on MSCs may help to better understand the molecular process underlying bone regeneration.

YAP and TAZ differentially regulate postnatal cortical progenitor proliferation and astrocyte differentiation

WW domain-containing transcription regulator 1 (WWTR1, referred to here as TAZ) and Yes-associated protein (YAP, also known as YAP1) are transcriptional co-activators traditionally studied together as a part of the Hippo pathway, and are best known for their roles in stem cell proliferation and differentiation. Despite their similarities, TAZ and YAP can exert divergent cellular effects by differentially interacting with other signaling pathways that regulate stem cell maintenance or differentiation. In this study, we show in mouse neural stem and progenitor cells (NPCs) that TAZ regulates astrocytic differentiation and maturation, and that TAZ mediates some, but not all, of the effects of bone morphogenetic protein (BMP) signaling on astrocytic development. By contrast, both TAZ and YAP mediate the effects on NPC fate of β1-integrin (ITGB1) and integrin-linked kinase signaling, and these effects are dependent on extracellular matrix cues. These findings demonstrate that TAZ and YAP perform divergent functions in the regulation of astrocyte differentiation, where YAP regulates cell cycle states of astrocytic progenitors and TAZ regulates differentiation and maturation from astrocytic progenitors into astrocytes.

Human iPSCs as Model Systems for BMP-Related Rare Diseases

Disturbances in bone morphogenetic protein (BMP) signalling contribute to onset and development of a number of rare genetic diseases, including Fibrodysplasia ossificans progressiva (FOP), Pulmonary arterial hypertension (PAH), and Hereditary haemorrhagic telangiectasia (HHT). After decades of animal research to build a solid foundation in understanding the underlying molecular mechanisms, the progressive implementation of iPSC-based patient-derived models will improve drug development by addressing drug efficacy, specificity, and toxicity in a complex humanized environment. We will review the current state of literature on iPSC-derived model systems in this field, with special emphasis on the access to patient source material and the complications that may come with it. Given the essential role of BMPs during embryonic development and stem cell differentiation, gain- or loss-of-function mutations in the BMP signalling pathway may compromise iPSC generation, maintenance, and differentiation procedures. This review highlights the need for careful optimization of the protocols used. Finally, we will discuss recent developments towards complex in vitro culture models aiming to resemble specific tissue microenvironments with multi-faceted cellular inputs, such as cell mechanics and ECM together with organoids, organ-on-chip, and microfluidic technologies.

The neural stem cell secretome across neurodevelopment

Neural stem cell (NSC) based therapies are at the forefront of regenerative medicine strategies to combat illness and injury of the central nervous system (CNS). In addition to their ability to produce new cells, NSCs secrete a variety of products, known collectively as the NSC secretome, that have been shown to ameliorate CNS disease pathology and promote recovery. As pre-clinical and clinical research to harness the NSC secretome for therapeutic purposes advances, a more thorough understanding of the endogenous NSC secretome can provide useful insight into the functional capabilities of NSCs. In this review, we focus on research investigating the autocrine and paracrine functions of the endogenous NSC secretome across life. Throughout development and adulthood, we find evidence that the NSC secretome is a critical component of how endogenous NSCs regulate themselves and their niche. We also find gaps in current literature, most notably in the clinically-relevant domain of endogenous NSC paracrine function in the injured CNS. Future investigations to further define the endogenous NSC secretome and its role in CNS tissue regulation are necessary to bolster our understanding of NSC-niche interactions and to aid in the generation of safe and effective NSC-based therapies.

Differential bioactivity of four BMP-family members as function of biomaterial stiffness

While a soft film itself is not able to induce cell spreading, BMP-2 presented via such soft film (so called "matrix-bound BMP-2") was previously shown to trigger cell spreading, migration and downstream BMP-2 signaling. Here, we used thin films of controlled stiffness presenting matrix-bound BMPs to study the effect of four BMP members (BMP-2, 4, 7, 9) on cell adhesion and differentiation of skeletal progenitors. We performed automated high-content screening of cellular responses, including cell number, cell spreading area, SMAD phosphorylation and alkaline phosphatase activity. We revealed that the cell response to bBMPs is BMP-type specific, and involved certain BMP receptors and beta chain integrins. In addition, this response is stiffness-dependent for several receptors. The basolateral presentation of the BMPs allowed us to discriminate the specificity of cellular response, especiallyd the role of type I and II BMP receptors and of β integrins in a BMP-type and stiffness-dependent manner. Notably, BMP-2 and BMP-4 were found to have distinct roles, while ALK5, previously known as a TGF-β receptor was revealed to be involved in the BMP-pathway.

Participation of Selected Soluble BMP-2 and BMP-7 Bone Morphogenetic Proteins and Their Soluble Type I ALK-1 and Type II BMPR2 Receptors in Formation and Development of Endometriosis

Angiogenesis is considered to be one of the key stages in the development of endometriosis. Recent studies indicate that bone morphogenetic proteins (BMPs) and their receptors (BMPR) may play an important role in the angiogenesis process. In the literature, however, there is a lack of publications concerning binding BMPs and their receptors with the pathogenesis of endometriosis. The aim of the study was to determine the role of soluble bone morphogenetic proteins, BMP-2 and BMP-7, and their receptors, ALK-1 and BMPR2, in the process of the formation and development of endometriosis. Peritoneal fluid was collected in the proliferative phase of the menstrual cycle, from 80 women aged 21-49 years (mean age 31.3 ± 6.7 years) undergoing laparoscopy to determine the causes of primary infertility. The study involved 60 women in the I, II, III, and IV stages of the disease. The reference group consisted of 20 women who did not have endometriosis or other lesions in the pelvic area. The concentration in the peritoneal fluid of women with endometriosis was compared to the concentration of this parameter in the reference group, and a statistically significant reduction in the concentration of the BMP-2 molecule was found, as well as increasing concentrations of BMP-7, ALK-1, and BMPR2. BMP-2 and BMP-7 and their soluble receptors, ALK-1 and BMPR2, are involved in the formation of endometriosis. The changes in the concentrations of most of the tested parameters demonstrated in the study, especially in the early stages of the disease, may indicate the more effective formation of new blood vessels in this period.

20 years of Hepcidin: How far we have come

Twenty years ago the discovery of hepcidin deeply changed our understanding of the regulation of systemic iron homeostasis. It is now clear that hepcidin orchestrates systemic iron levels by controlling the amount of iron exported into the bloodstream through ferroportin. Hepcidin expression is increased in situations where systemic iron levels should be reduced, such as in iron overload and infection. Conversely, hepcidin is repressed during iron deficiency, hypoxia or expanded erythropoiesis, to increase systemic iron availability and sustain erythropoiesis. In this review, we will focus on molecular mechanisms of hepcidin regulation and on the pathological consequences of their disruption.

BMP signalling in a mechanical context - Implications for bone biology

Bone Morphogenetic Proteins (BMPs) are extracellular multifunctional signalling cytokines and members of the TGFβ super family. These pleiotropic growth factors crucially promote bone formation, remodeling and healing after injury. Additionally, bone homeostasis is systematically regulated by mechanical inputs from the environment, which are incorporated into the bone cells' biochemical response. These inputs range from compression and tension induced by the movement of neighboring muscle, to fluid shear stress induced by interstitial fluid flow in the canaliculi and in the vascular system. Although BMPs are widely applied in a clinic context to promote fracture healing, it is still elusive how mechanical inputs modulate this signalling pathway, hindering an efficient and side-effect free application of these ligands in bone healing. This review aims to summarize the current understanding in how mechanical cues (tension, compression, shear force and hydrostatic pressure) and substrate stiffness modulate BMP signalling. We highlight the time-dependent effects in modulating immediate early up to long-term effects of mechano-BMP crosstalk during bone formation and remodeling, considering the interplay with other already established mechanosensitive pathways, such as MRTF/SRF and Hippo signalling.

Integrins Modulate Extracellular Matrix Organization to Control Cell Signaling during Hematopoiesis

During hematopoiesis, progenitor cells receive and interpret a diverse array of regulatory signals from their environment. These signals control the maintenance of the progenitors and regulate the production of mature blood cells. Integrins are well known in vertebrates for their roles in hematopoiesis, particularly in assisting in the migration to, as well as the physical attachment of, progenitors to the niche. However, whether and how integrins are also involved in the signaling mechanisms that control hematopoiesis remains to be resolved. Here, we show that integrins play a key role during fly hematopoiesis in regulating cell signals that control the behavior of hematopoietic progenitors. Integrins can regulate hematopoiesis directly, via focal adhesion kinase (FAK) signaling, and indirectly, by directing extracellular matrix (ECM) assembly and/or maintenance. ECM organization and density controls blood progenitor behavior by modulating multiple signaling pathways, including bone morphogenetic protein (BMP) and Hedgehog (Hh). Furthermore, we show that integrins and the ECM are reduced following infection, which may assist in activating the immune response. Our results provide mechanistic insight into how integrins can shape the signaling environment around hematopoietic progenitors.

Screening as a strategy to drive regenerative medicine research

In the field of regenerative medicine, optimization of the parameters leading to a desirable outcome remains a huge challenge. Examples include protocols for the guided differentiation of pluripotent cells towards specialized and functional cell types, phenotypic maintenance of primary cells in cell culture, or engineering of materials for improved tissue interaction with medical implants. This challenge originates from the enormous design space for biomaterials, chemical and biochemical compounds, and incomplete knowledge of the guiding biological principles. To tackle this challenge, high-throughput platforms allow screening of multiple perturbations in one experimental setup. In this review, we provide an overview of screening platforms that are used in regenerative medicine. We discuss their fabrication techniques, and in silico tools to analyze the extensive data sets typically generated by these platforms.

Bone marrow niche crosses paths with BMPs: a road to protection and persistence in CML

Chronic myeloid leukaemia (CML) is a paradigm of precision medicine, being one of the first cancers to be treated with targeted therapy. This has revolutionised CML therapy and patient outcome, with high survival rates. However, this now means an ever-increasing number of patients are living with the disease on life-long tyrosine kinase inhibitor (TKI) therapy, with most patients anticipated to have near normal life expectancy. Unfortunately, in a significant number of patients, TKIs are not curative. This low-level disease persistence suggests that despite a molecularly targeted therapeutic approach, there are BCR-ABL1-independent mechanisms exploited to sustain the survival of a small cell population of leukaemic stem cells (LSCs). In CML, LSCs display many features akin to haemopoietic stem cells, namely quiescence, self-renewal and the ability to produce mature progeny, this all occurs through intrinsic and extrinsic signals within the specialised microenvironment of the bone marrow (BM) niche. One important avenue of investigation in CML is how the disease highjacks the BM, thereby remodelling this microenvironment to create a niche, which enables LSC persistence and resistance to TKI treatment. In this review, we explore how changes in growth factor levels, in particular, the bone morphogenetic proteins (BMPs) and pro-inflammatory cytokines, impact on cell behaviour, extracellular matrix deposition and bone remodelling in CML. We also discuss the challenges in targeting LSCs and the potential of dual targeting using combination therapies against BMP receptors and BCR-ABL1.

Bone formation activity of an osteogenic dodecapeptide from blue mussels (Mytilus edulis)

A novel osteogenic dodecapeptide peptide (PIE), IEELEEELEAER, was purified from the protein hydrolysate of blue mussels (Mytilus edulis). PIE was identified using a capillary electrophoresis electrospray ionization-quadrupole-time of flight mass spectrometer. PIE showed a good reduction in the bone loss in ovariectomized mice, and it also increased the bone mineral density of the ovariectomized mice. PIE has a high affinity with integrins (PDB: , ). There are 8 and 12 amino acid residues from PIE that interact with integrins and , respectively. PIE accelerates the transformation of G0/G1 phase cells into G2 M phase cells, which promotes the growth of osteoblasts. PIE (100 μg mL^-1) can enhance alkaline phosphatase (ALP) activity by 26.48% compared with the control, and it also inhibits the growth of osteoclasts and tartrate resistant acid phosphatase (TRAP) activity. Therefore, PIE may contribute to preventing osteoporosis both in vitro and in vivo.

Engineered delivery strategies for enhanced control of growth factor activities in wound healing

Growth factors (GFs) are versatile signalling molecules that orchestrate the dynamic, multi-stage process of wound healing. Delivery of exogenous GFs to the wound milieu to mediate healing in an active, physiologically-relevant manner has shown great promise in laboratories; however, the inherent instability of GFs, accompanied with numerous safety, efficacy and cost concerns, has hindered the clinical success of GF delivery. In this article, we highlight that the key to overcoming these challenges is to enhance the control of the activities of GFs throughout the delivering process. We summarise the recent strategies based on biomaterials matrices and molecular engineering, which aim to improve the conditions of GFs for delivery (at the 'supply' end of the delivery), increase the stability and functions of GFs in extracellular matrix (in transportation to target cells), as well as enhance the GFs/receptor interaction on the cell membrane (at the 'destination' end of the delivery). Many of these investigations have led to encouraging outcomes in various in vitro and in vivo regenerative models with considerable translational potential.

Isolation and Characterization of Peptides from Mytilus edulis with Osteogenic Activity in Mouse MC3T3-E1 Preosteoblast Cells

Seafood provides a range of health benefits because of its high protein levels. In this study, a novel peptide, YPRKDETGAERT, was identified from NHA-2 of Mytilus edulis by capillary-electrophoresis electrospray ionization-quadrupole-time of flight (CESI-Q-TOF). Peptide YPRKDETGAERT showed the highest affinity among all the peptides, with -CDOCKER energy values of 204.482 kcal/mol on one integrin (PDB: 3VI4 ) and 210.16 kcal/mol on another integrin (PDB: 1L5G ). The secondary mass spectrogram at the m/ z of peptide YPRKDETGAERT was 1422.53 Da, which was determined by CESI-Q-TOF. Peptide YPRKDETGAERT induced an increase of 28.27 ± 3.66% in mouse-MC3T3-E1-preosteoblast-cell growth. The alkaline-phosphatase activity of peptide YPRKDETGAERT was 2.79 ± 0.07 mU, which was an increase of 21.25% compared with that of the control. These results provide theoretical and practical insights for the preparation and application of osteogenic peptides in the functional-foods industry.

Integrin-Linked Kinase Regulates Bone Formation by Controlling Cytoskeletal Organization and Modulating BMP and Wnt Signaling in Osteoprogenitors

Cell-matrix interactions constitute a fundamental aspect of skeletal cell biology and play essential roles in bone homeostasis. These interactions are primarily mediated by transmembrane integrin receptors, which mediate cell adhesion and transduce signals from the extracellular matrix to intracellular responses via various downstream effectors, including integrin-linked kinase (ILK). ILK functions as adaptor protein at focal adhesion sites, linking integrins to the actin cytoskeleton, and has been reported to act as a kinase phosphorylating signaling molecules such as GSK-3β and Akt. Thereby, ILK plays important roles in cellular attachment, motility, proliferation and survival. To assess the in vivo role of ILK signaling in osteoprogenitors and the osteoblast lineage cells descending thereof, we generated conditional knockout mice using the Osx-Cre:GFP driver strain. Mice lacking functional ILK in osterix-expressing cells and their derivatives showed no apparent developmental or growth phenotype, but by 5 weeks of age they displayed a significantly reduced trabecular bone mass, which persisted into adulthood in male mice. Histomorphometry and serum analysis indicated no alterations in osteoclast formation and activity, but provided evidence that osteoblast function was impaired, resulting in reduced bone mineralization and increased accumulation of unmineralized osteoid. In vitro analyses further substantiated that absence of ILK in osteogenic cells was associated with compromised collagen matrix production and mineralization. Mechanistically, we found evidence for both impaired cytoskeletal functioning and reduced signal transduction in osteoblasts lacking ILK. Indeed, loss of ILK in primary osteogenic cells impaired F-actin organization, cellular adhesion, spreading, and migration, indicative of defective coupling of cell-matrix interactions to the cytoskeleton. In addition, BMP/Smad and Wnt/β-catenin signaling was reduced in the absence of ILK. Taken together, these data demonstrate the importance of integrin-mediated cell-matrix interactions and ILK signaling in osteoprogenitors in the control of osteoblast functioning during juvenile bone mass acquisition and adult bone remodeling and homeostasis. © 2017 American Society for Bone and Mineral Research.