Injectable decellularized extracellular matrix hydrogel promotes salivary gland regeneration via endogenous stem cell recruitment and suppression of fibrogenesis

Saliva is key to the maintenance of oral homeostasis. However, several forms of salivary gland (SG) disorders, followed by hyposalivation, often result in dental caries, oral infection, and decreased taste, which dramatically affect the quality of patient's life. Functional biomaterials hold great potential for tissue regeneration in damaged or dysfunctional SGs and maintaining the good health of oral cavity. Herein, we prepared an injectable hydrogel derived from decellularized porcine submandibular glands (pDSG-gel), the material and biological properties of the hydrogel were systematically investigated. First, good biocompatibility and bioactivities of the pDSG-gel were validated in 2D and 3D cultures of primary submandibular gland mesenchymal stem cells (SGMSCs). Especially, the pDSG-gel effectively facilitated SGMSCs migration and recruitment through the activation of PI3K/AKT signaling pathway, suggested by transcriptomic analysis and immunoblotting. Furthermore, proteomic analysis of the pDSG revealed that many extracellular matrix components and secreted factors were preserved, which may contribute to stem cell homing. The recruitment of endogenous SG cells was confirmed in vivo, upon in situ injection of the pDSG-gel into the defective SGs in rats. Acinar and ductal-like structures were evident in the injury sites after pDSG-gel treatment, suggesting the reconstruction of functional SG units. Meanwhile, histological characterizations showed that the administration of the pDSG-gel also significantly suppressed fibrogenesis within the injured SG tissues. Taken together, this tissue-specific hydrogel provides a pro-regenerative microenvironment for endogenous SG regeneration and holds great promise as a powerful and bioactive material for future treatments of SG diseases. STATEMENT OF SIGNIFICANCE: Decellularized extracellular matrix (dECM) has been acknowledged as one of the most promising biomaterials that recapitalizes the microenvironment in native tissues. Hydrogel derived from the dECM allows in situ administration for tissue repair. Herein, a tissue-specific dECM hydrogel derived from porcine salivary glands (pDSG-gel) was successfully prepared and developed for functional reconstruction of defective salivary gland (SG) tissues. The pDSG-gel effectively accelerated endogenous SG stem cells migration and their recruitment for acinar- and ductal-like regeneration, which was attributed to the activation of PI3K/AKT signaling pathway. Additionally, the introduction of the pDSG-gel resulted in highly suppressed fibrogenesis in the defective tissues. These outcomes indicated that the pDSG-gel holds great potential in clinical translation toward SG regeneration through cell-free treatments.

Advanced bioactive glue tethering Lubricin/PRG4 to promote integrated healing of avascular meniscus tears

Meniscus injuries are extremely common with approximately one million patients undergoing surgical treatment annually in the U.S. alone, but no regenerative therapy exist. Previously, we showed that controlled applications of connective tissue growth factor (CTGF) and transforming growth factor beta 3 (TGFβ3) via fibrin-based bio-glue facilitate meniscus healing by inducing recruitment and stepwise differentiation of synovial mesenchymal stem/progenitor cells. Here, we first explored the potential of genipin, a natural crosslinker, to enhance fibrin-based glue's mechanical and degradation properties. In parallel, we identified the harmful effects of lubricin on meniscus healing and investigated the mechanism of lubricin deposition on the injured meniscus surface. We found that the pre-deposition of hyaluronic acid (HA) on the torn meniscus surface mediates lubricin deposition. Then we implemented chemical modifications with heparin conjugation and CD44 on our bioactive glue to achieve strong initial bonding and integration of lubricin pre-coated meniscal tissues. Our data suggested that heparin conjugation significantly enhances lubricin-coated meniscal tissues. Similarly, CD44, exhibiting a strong binding affinity to lubricin and hyaluronic acid (HA), further improved the integrated healing of HA/lubricin pre-coated meniscus injuries. These findings may represent an important foundation for developing a translational bio-active glue guiding the regenerative healing of meniscus injuries.

Combined effect of SDF-1 peptide and angiogenic cues in co-axial PLGA/gelatin fibers for cutaneous wound healing in diabetic rats

Skin regeneration is hindered by poor vascularization, prolonged inflammation, and excessive scar tissue formation, which necessitate newer strategies to simultaneously induce blood vessel regeneration, resolve inflammation, and induce host cell recruitment. Concurrent deployment of multiple biological cues to realize synergistic reparative effects may be an enticing avenue for wound healing. Herein, we simultaneously deployed SDF (stromal cell-derived factor)- 1α, VEGF (vascular endothelial growth factor)-binding peptide (BP), and GLP (glucagon like peptide)- 1 analog, liraglutide (LG) in core/shell poly(L-lactide-co-glycolide)/gelatin fibers to harness their synergistic effects for skin repair in healthy as well as diabetic wound models in rats. Microscopic techniques, such as SEM and TEM revealed fibrous and core/shell type morphology of membranes. Boyden chamber assay and scratch-wound assay displayed significant migration of HUVECs (human umbilical vein endothelial cells) in SDF-1α containing fibers. Subcutaneous implantation of membranes revealed higher cellular infiltration in SDF-1α loaded fibers, especially, those which were co-loaded with LG or BP. Implantation of membranes in an excisional wound model in healthy rats further showed significant and rapid wound closure in dual cues loaded groups as compared to control or single cue loaded groups. Similarly, the implantation of dressings in type 2 diabetes rat model revealed fast healing, skin appendages regeneration, and blood vessel regeneration in dual cues loaded fibers (SDF-1α/LG, SDF-1α/BP). Taken together, core/shell type fibers containing bioactive peptides significantly promoted wound repair in healthy as well as diabetic wound models in rats.

A cell-free difunctional demineralized bone matrix scaffold enhances the recruitment and osteogenesis of mesenchymal stem cells by promoting inflammation resolution

The dialogue between host macrophages (Mφs) and endogenous mesenchymal stem cells (MSCs) promotes M2 Mφs polarization to resolve early-stage inflammation, thereby effectively guiding in situ bone regeneration. Once inflammation is unresolved/incontrollable, it will induce the impediment of MSCs homing at bone defect site, implying the seasonable resolution of inflammation in balancing bone homeostasis. Repeatedly, evidence elucidated that specialized pro-resolving mediators (SPMs) could conduce to proper resolve inflammation and promote the repairing of bone defect. A difunctional demineralized bone matrix (DBM) scaffold co-modified by maresin 1 (MaR1) and aptamer 19S (Apt19S) was fabricated to facilitate the osteogenesis of MSCs. To confirm the osteogenesis and immunomodulatory role of the difunctional DBM scaffold, the proliferation, recruitment, and osteogenic differentiation of MSCs and the Mφs M2 subtype polarization were evaluated in vitro. Then, the DBM scaffolds were implanted into mice model with critical size calvarial defect to evaluate bone repair efficiency. Finally, the specific resolution mechanism in Mφs cultured on the difunctional DBM scaffold was further in-depth investigated. This difunctional DBM scaffold exhibited an enhanced function on the recruitment, proliferation, migration, osteogenesis of MSCs and the resolution of inflammation, finally improved bone-scaffold integration. At the same time, MaR1 modified on the difunctional DBM scaffold increased the biosynthesis of 12-lipoxygenase (12-LOX) and 12S-hydroxy-eicosatetraenoic acid (12S-HETE), and also directly stimulated lipid droplets (LDs) biogenesis in Mφs, which suggested that MaR1 regulated Mφ lipid metabolism at bone repair site. Findings based on this synergy strategy demonstrated that Mφ lipid metabolism was essential in bone homeostasis, which might provide a theoretical direction for the treatment-associated application of MaR1 in inflammatory bone disease.

Biomaterials for recruiting and activating endogenous stem cells in situ tissue regeneration

Over the past two decades in situ tissue engineering has emerged as a new approach where biomaterials are used to harness the body's own stem/progenitor cells to regenerate diseased or injured tissue. Immunomodulatory biomaterials are designed to promote a regenerative environment, recruit resident stem cells to diseased or injured tissue sites, and direct them towards tissue regeneration. This review explores advances gathered from in vitro and in vivo studies on in situ tissue regenerative therapies. Here we also examine the different ways this approach has been incorporated into biomaterial sciences in order to create customized biomaterial products for therapeutic applications in a broad spectrum of tissues and diseases. STATEMENT OF SIGNIFICANCE: Biomaterials can be designed to recruit stem cells and coordinate their behavior and function towards the restoration or replacement of damaged or diseased tissues in a process known as in situ tissue regeneration. Advanced biomaterial constructs with precise structure, composition, mechanical, and physical properties can be transplanted to tissue site and exploit local stem cells and their micro-environment to promote tissue regeneration. In the absence of cells, we explore the critical immunomodulatory, chemical and physical properties to consider in material design and choice. The application of biomaterials for in situ tissue regeneration has the potential to address a broad range of injuries and diseases.

Bioinspired Andrias davidianus-Derived wound dressings for localized drug-elution

Local drug delivery has received increasing attention in recent years. However, the therapeutic efficacy of local delivery of drugs is still limited under certain scenarios, such as in the oral cavity or in wound beds after resection of tumors. In this study, we introduce a bioinspired adhesive hydrogel derived from the skin secretions of Andrias davidianus (SSAD) as a wound dressing for localized drug elution. The hydrogel was loaded with aminoguanidine or doxorubicin, and its controlled drug release and healing-promoting properties were verified in a diabetic rat palatal mucosal defect model and a C57BL/6 mouse melanoma-bearing model, respectively. The results showed that SSAD hydrogels with different pore sizes could release drugs in a controllable manner and accelerate wound healing. Transcriptome analyses of the palatal mucosa suggested that SSAD could significantly upregulate pathways linked to cell adhesion and extracellular matrix deposition and had the ability to recruit keratinocyte stem cells to defect sites. Taken together, these findings indicate that property-controllable SSAD hydrogels could be a promising biofunctional wound dressing for local drug delivery and promotion of wound healing.

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The SSAD is a biologically drawable source with facile production, cost-effective, and safe.

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SSAD increases drug bioavailability with local application.

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The drug release rate can be controlled by regulating SSAD particle size.

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The SSAD-based wound dressing is adhesive.

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SSAD can also promote wound healing.

Cell-free decellularized cartilage extracellular matrix scaffolds combined with interleukin 4 promote osteochondral repair through immunomodulatory macrophages: In vitro and in vivo preclinical study

Cartilage regeneration is a complex physiological process. Synovial macrophages play a critical immunomodulatory role in the acute inflammatory response surrounding joint injury. Due to the contrasting differences and heterogeneity of macrophage, the phenotype of macrophages are the key determinants of the healing response after cartilage injury. Biomaterials derived from extracellular matrix have been used for the repair and reconstruction of a variety of tissues by modulating the host macrophage response. However, the immunomodulatory effect of decellularized cartilage extracellular matrix (ECM) on macrophages has not been elucidated. It is necessary to clarify the immunomodulatory properties of decellularized cartilage matrix (DCM) to guide the design of cartilage regeneration materials. Here, we prepared porcine articular cartilage derived DCM and determined the response of mouse bone marrow-derived macrophages (BMDMs) to the pepsin-solubilized DCM (PDCM) in vitro. Macrophages activated by the PDCM could promote bone marrow-derived mesenchymal stem cells (BMSCs) invasion, migration, proliferation, and chondrogenic differentiation. Then, we verified that early optimization of the immunomodulatory effects of the cell-free DCM scaffold using IL-4 in vivo could achieve good cartilage regeneration in a rat knee osteochondral defect model. Therefore, this decellularized cartilage ECM scaffold combined with accurate and active immunomodulatory strategies provides a new approach for the development of cartilage regeneration materials. STATEMENT OF SIGNIFICANCE: This work reports a decellularized cartilage extracellular matrix (DCM) scaffold combined with an accurate and active immunomodulatory strategy to improve cartilage regeneration. Our findings demonstrated that the pepsin-solubilized DCM (PDCM) activated bone marrow-derived macrophages to polarize to a constructive macrophage phenotype. These polarized macrophages promoted bone marrow-derived mesenchymal stem cell invasion, migration, proliferation, and chondrogenic differentiation. DCM scaffolds combined with early-stage intra-articular injection of IL-4 created a wound-healing microenvironment and improved cartilage regeneration in a rat knee osteochondral defect model.

Complement activation links inflammation to dental tissue regeneration

OBJECTIVES

Complement is an efficient plasma immune surveillance system. It initiates inflammation by inducing vascular modifications and attracting immune cells expressing Complement receptors. Investigating Complement receptors in non-immune cells pointed out Complement implication in the regeneration of tissue such as liver, skin, or bone. This review will shed the light on Complement implication in the initial steps of dental tissue regeneration.

MATERIALS AND METHODS

Review of literature was conducted on Complement local expression and implication in oral tissue regeneration in vivo and in vitro.

RESULTS

Recent data reported expression of Complement receptors and soluble proteins in dental tissues. Cultured pulp fibroblasts secrete all Complement components. Complement C3b and MAC have been shown to control bacteria growth in the dental pulp while C3a and C5a are involved in the initial steps of pulp regeneration. Indeed, C3a induces pulp stem cell/fibroblast proliferation, and fibroblast recruitment, while C5a induces neurite growth, guides stem cell recruitment, and odontoblastic differentiation. Similarly, cultured periodontal ligament cells produce C5a which induces bone marrow mesenchymal stem cell recruitment.

CONCLUSIONS

Overall, this review highlights that local Complement synthesis in dental tissues plays a major role, not only in eliminating bacteria but also in the initial steps of dental tissue regeneration, thus providing a link between dental tissue inflammation and regeneration.

CLINICAL RELEVANCE

Complement provides an explanation for understanding why inflammation preceeds regeneration. This may also provide a biological rational for understanding the reported success conservative management of mature permanent teeth with carious pulp exposure.

Xenogeneic bone filling materials modulate mesenchymal stem cell recruitment: role of the Complement C5a

OBJECTIVES

When bone filling materials are applied onto the periodontal tissues in vivo, they interact with the injured periodontal ligament (PDL) tissue and modulate its activity. This may lead to mesenchymal stem cells (MSCs) recruitment from bone marrow and initiate bone regeneration. Our hypothesis is that the filling materials affect PDL cells and MSCs functional activities by modulating PDL C5a secretion and subsequent MSCs proliferation and recruitment.

MATERIALS AND METHODS

Materials' extracts were prepared from 3 bone-grafting materials: Gen-Os^® of equine and porcine origins and bovine Bio-Oss^®. Expression and secretion of C5a protein by injured PDL cells were investigated by RT-PCR and ELISA. MSCs proliferation was analyzed by MTT assay. C5a binding to MSCs C5aR and its phosphorylation was studied by ELISA. C5a implication in MSCs recruitment toward injured PDL cells was investigated using Boyden chambers.

RESULTS

MSCs proliferation significantly increased with Gen-Os^® materials but significantly decreased with Bio-Oss^®. C5a secretion slightly increased with Bio-Oss^® while its level doubled with Gen-Os^® materials. C5a fixation on MSCs C5aR and its phosphorylation significantly increased with Gen-Os^® materials but not with Bio-Oss^®. MSCs recruitment toward injured PDL cells increased with the three materials but was significantly higher with Gen-Os^® materials than with Bio-Oss^®. Adding C5a antagonist inhibited MSCs recruitment demonstrating a C5a-mediated migration.

CONCLUSIONS

Injured PDL cells secrete C5a leading MSCs proliferation and recruitment to the PDL injured cells. Gen-Os^® materials enhanced both C5a secretion by injured PDL cells and MSCs recruitment. Bio-Oss^® inhibited MSCs and was less efficient than Gen-Os^® materials in inducing MSCs recruitment.

CLINICAL RELEVANCE

Within the limits of this study in vitro, Gen-Os^® filling materials have a higher potential than Bio-Oss^® on MSCs proliferation and C5a-dependent recruitment to the PDL injury site and the subsequent bone regeneration.

Evaluation of an Engineered Hybrid Matrix for Bone Regeneration via Endochondral Ossification

Despite its regenerative ability, long and segmental bone defect repair remains a significant orthopedic challenge. Conventional tissue engineering efforts induce bone formation through intramembranous ossification (IO) which limits vascular formation and leads to poor bone regeneration. To overcome this challenge, a novel hybrid matrix comprised of a load-bearing polymer template and a gel phase is designed and assessed for bone regeneration. Our previous studies developed a synthetic ECM, hyaluronan (HA)-fibrin (FB), that is able to mimic cartilage-mediated bone formation in vitro. In this study, the well-characterized HA-FB hydrogel is combined with a biodegradable polymer template to form a hybrid matrix. In vitro evaluation of the matrix showed cartilage template formation, cell recruitment and recruited cell osteogenesis, essential stages in endochondral ossification. A transgenic reporter-mouse critical-defect model was used to evaluate the bone healing potential of the hybrid matrix in vivo. The results demonstrated host cell recruitment into the hybrid matrix that led to new bone formation and subsequent remodeling of the mineralization. Overall, the study developed and evaluated a novel load-bearing graft system for bone regeneration via endochondral ossification.

A collagen hydrogel loaded with HDAC7-derived peptide promotes the regeneration of infarcted myocardium with functional improvement in a rodent model

Myocardial infarction (MI) leads to the loss of cardiomyocytes, left ventricle (LV) dilation, and cardiac dysfunction, eventually developing into heart failure. Most of the strategies for MI therapy require biomaterials that can support tissue regeneration. In this study, we hypothesized that the extracellular matrix (ECM)-derived collagen I hydrogel loaded with histone deacetylase 7 (HDAC7)-derived-phosphorylated 7-amino-acid peptide (7Ap) could restrain LV remodeling and improve cardiac function after MI. An MI model was established by ligation of the left anterior descending coronary artery (LAD) of C57/B6 mice. The 7Ap-loaded collagen I hydrogel was intramyocardially injected to the infarcted region of the LV wall of the heart. After local delivery, the 7Ap-collagen increased neo-microvessel formation, enhanced stem cell antigen-1 positive (Sca-1⁺) stem cell recruitment and differentiation, decreased cellular apoptosis, and promoted cardiomyocyte cycle progression. Furthermore, the 7Ap-collagen restricted the fibrosis of the LV wall, reduced the infarct wall thinning, and improved cardiac performance significantly at 2 weeks post-MI. These results highlight the promising implication of 7Ap-collagen as a novel candidate for MI therapy. STATEMENT OF SIGNIFICANCE: The mammalian myocardium has a limited regenerative capability following myocardial infarction (MI). MI leads to extensive loss of cardiomyocytes, thus culminating in adverse cardiac remodeling and congestive heart failure. In situ tissue regeneration through endogenous cell mobilization has great potential for tissue regeneration. A 7-amino-acid-peptide (7A) domain encoded by a short open-reading frame (sORF) of the HDAC7 gene. The phosphorylated from of 7A (7Ap) has been reported to promote in situ tissue repair via the mobilization and recruitment of endogenous stem cell antigen-1 positive (Sca-l⁺) stem cells. In this study, 7Ap was shown to improve H9C2 cell survival, in vitro. In vivo investigations in a mouse MI model demonstrated that intra-myocardial delivery of 7Ap-loaded collagen hydrogel promoted neovascularization, stimulated Sca-l⁺ stem cell recruitment and differentiation, reduced cardiomyocyte apoptosis and promoted cell cycle progression. As a result, treated infarcted hearts had increased wall thickness, had improved heart function and exhibited attenuation of adverse cardiac remodeling, observed for up to 2 weeks. Overall, these results highlighted the positive impact of implanting 7Ap-collagen as a novel constituent for MI repair.

Mechano growth factor (MGF) and transforming growth factor (TGF)-β3 functionalized silk scaffolds enhance articular hyaline cartilage regeneration in rabbit model

Damaged cartilage has poor self-healing ability and usually progresses to scar or fibrocartilaginous tissue, and finally degenerates to osteoarthritis (OA). Here we demonstrated that one of alternative isoforms of IGF-1, mechano growth factor (MGF) acted synergistically with transforming growth factor β3 (TGF-β3) embedded in silk fibroin scaffolds to induce chemotactic homing and chondrogenic differentiation of mesenchymal stem cells (MSCs). Combination of MGF and TGF-β3 significantly increased cell recruitment up to 1.8 times and 2 times higher than TGF-β3 did in vitro and in vivo. Moreover, MGF increased Collagen II and aggrecan secretion of TGF-β3 induced hMSCs chondrogenesis, but decreased Collagen I in vitro. Silk fibroin (SF) scaffolds have been widely used for tissue engineering, and we showed that methanol treated pured SF scaffolds were porous, similar to compressive module of native cartilage, slow degradation rate and excellent drug released curves. At 7 days after subcutaneous implantation, TGF-β3 and MGF functionalized silk fibroin scaffolds (STM) recruited more CD29+/CD44+cells (P<0.05). Similarly, more cartilage-like extracellular matrix and less fibrillar collagen were detected in STM scaffolds than that in TGF-β3 modified scaffolds (ST) at 2 months after subcutaneous implantation. When implanted into articular joints in a rabbit osteochondral defect model, STM scaffolds showed the best integration into host tissues, similar architecture and collagen organization to native hyaline cartilage, as evidenced by immunostaining of aggrecan, collagen II and collagen I, as well as Safranin O and Masson's trichrome staining, and histological evalution based on the modified O'Driscoll histological scoring system (P<0.05), indicating that MGF and TGF-β3 might be a better candidate for cartilage regeneration. This study demonstrated that TGF-β3 and MGF functionalized silk fibroin scaffolds enhanced endogenous stem cell recruitment and facilitated in situ articular cartilage regeneration, thus providing a novel strategy for cartilage repair.