PHD-2 Suppression in Mesenchymal Stromal Cells Enhances Wound Healing

PHD1-3 oxygen sensors in vivo-lessons learned from gene deletions

Oxygen sensors enable cells to adapt to limited oxygen availability (hypoxia), affecting various cellular and tissue responses. Prolyl-4-hydroxylase domain 1-3 (PHD1-3; also called Egln1-3, HIF-P4H 1-3, HIF-PH 1-3) proteins belong to the Fe2+- and 2-oxoglutarate-dependent dioxygenase superfamily and utilise molecular oxygen (O2) alongside 2-oxoglutarate as co-substrate to hydroxylate two proline residues of α subunits of the dimeric hypoxia inducible factor (HIF) transcription factor. PHD1-3-mediated hydroxylation of HIF-α leads to its degradation and inactivation. Recently, various PHD inhibitors (PHI) have entered the clinics for treatment of renal anaemia. Pre-clinical analyses indicate that PHI treatment may also be beneficial in numerous other hypoxia-associated diseases. Nonetheless, the underlying molecular mechanisms of the observed protective effects of PHIs are only partly understood, currently hindering their translation into the clinics. Moreover, the PHI-mediated increase of Epo levels is not beneficial in all hypoxia-associated diseases and PHD-selective inhibition may be advantageous. Here, we summarise the current knowledge about the relevance and function of each of the three PHD isoforms in vivo, based on the deletion or RNA interference-mediated knockdown of each single corresponding gene in rodents. This information is crucial for our understanding of the physiological relevance and function of the PHDs as well as for elucidating their individual impact on hypoxia-associated diseases. Furthermore, this knowledge highlights which diseases may best be targeted by PHD isoform-selective inhibitors in case such pharmacologic substances become available.

Targeting Signalling Pathways in Chronic Wound Healing

Chronic wounds fail to achieve complete closure and are an economic burden to healthcare systems due to the limited treatment options and constant medical attention. Chronic wounds are characterised by dysregulated signalling pathways. Research has focused on naturally derived compounds, stem-cell-based therapy, small molecule drugs, oligonucleotide delivery nanoparticles, exosomes and peptide-based platforms. The phosphoinositide-3-kinase (PI3K)/protein kinase B (AKT), Wingless-related integration (Wnt)/β-catenin, transforming growth factor-β (TGF-β), nuclear factor erythroid 2-related factor 2 (Nrf2), Notch and hypoxia-inducible factor 1 (HIF-1) signalling pathways have critical roles in wound healing by modulating the inflammatory, proliferative and remodelling phases. Moreover, several regulators of the signalling pathways were demonstrated to be potential treatment targets. In this review, the current research on targeting signalling pathways under chronic wound conditions will be discussed together with implications for future studies.

Tissue-Oxygen-Adaptation of Bone Marrow-Derived Mesenchymal Stromal Cells Enhances Their Immunomodulatory and Pro-Angiogenic Capacity, Resulting in Accelerated Healing of Chemical Burns

Transplantation of mesenchymal stromal cells (MSCs) provides a powerful tool for the management of multiple tissue injuries. However, poor survival of exogenous cells at the site of injury is a major complication that impairs MSC therapeutic efficacy. It has been found that tissue-oxygen adaptation or hypoxic pre-conditioning of MSCs could improve the healing process. Here, we investigated the effect of low oxygen tension on the regenerative potential of bone-marrow MSCs. It turned out that incubation of MSCs under a 5% oxygen atmosphere resulted in increased proliferative activity and enhanced expression of multiple cytokines and growth factors. Conditioned growth medium from low-oxygen-adapted MSCs modulated the pro-inflammatory activity of LPS-activated macrophages and stimulated tube formation by endotheliocytes to a much higher extent than conditioned medium from MSCs cultured in a 21% oxygen atmosphere. Moreover, we examined the regenerative potential of tissue-oxygen-adapted and normoxic MSCs in an alkali-burn injury model on mice. It has been revealed that tissue-oxygen adaptation of MSCs accelerated wound re-epithelialization and improved the tissue histology of the healed wounds in comparison with normoxic MSC-treated and non-treated wounds. Overall, this study suggests that MSC adaptation to 'physiological hypoxia' could be a promising approach for facilitating skin injuries, including chemical burns.

Regulatory T Cells in Development and Prediction of Necrotizing Enterocolitis in Preterm Neonates: A Scoping Review

Necrotizing enterocolitis (NEC) is a leading cause of mortality in premature infants. However, the pathophysiology and influence of regulatory T cells (Tregs) have not been sufficiently elucidated. We performed a scoping review to investigate current knowledge on the influence of Tregs in NEC, and to investigate the predictive value of Treg number in NEC development. Pubmed, Embase, Prospero and Cochrane Library were searched during December 2020. Primary research articles discussing Tregs and NEC development written in English were selected. Two reviewers screened title and abstract for relevance, after which full-text screening was performed. A total of 20 articles were selected-13 of the articles discussed studies performed in animal models, while 8 used human neonate data. One study discussed both animal and human data. It was shown that after NEC diagnosis or induction, Treg levels were decreased while Th17 levels were increased. No studies were found which investigated the predictive value of Treg number in NEC development. A reduced Treg level is found in animals and neonates with NEC. The question remains whether this effect is a factor on the causal pathway of NEC development or a bystander effect. Future research focusing on the pathophysiological timeline of NEC and the involvement of Tregs is required for better understanding of this disease.

Impact of High-Altitude Hypoxia on Bone Defect Repair: A Review of Molecular Mechanisms and Therapeutic Implications

Reaching areas at altitudes over 2,500–3,000 m above sea level has become increasingly common due to commerce, military deployment, tourism, and entertainment. The high-altitude environment exerts systemic effects on humans that represent a series of compensatory reactions and affects the activity of bone cells. Cellular structures closely related to oxygen-sensing produce corresponding functional changes, resulting in decreased tissue vascularization, declined repair ability of bone defects, and longer healing time. This review focuses on the impact of high-altitude hypoxia on bone defect repair and discusses the possible mechanisms related to ion channels, reactive oxygen species production, mitochondrial function, autophagy, and epigenetics. Based on the key pathogenic mechanisms, potential therapeutic strategies have also been suggested. This review contributes novel insights into the mechanisms of abnormal bone defect repair in hypoxic environments, along with therapeutic applications. We aim to provide a foundation for future targeted, personalized, and precise bone regeneration therapies according to the adaptation of patients to high altitudes.

Lactic acid in macrophage polarization: The significant role in inflammation and cancer

Metabolite lactic acid has always been regarded as a metabolic by-product rather than a bioactive molecule. Recently, this view has changed since it was discovered that lactic acid can be used as a signal molecule and has novel signal transduction functions both intracellular and extracellular, which can regulate key functions in the immune system. In recent years, more and more evidence has shown that lactic acid is closely related to the metabolism and polarization of macrophages. During inflammation, lactic acid is a regulator of macrophage metabolism, and it can prevent excessive inflammatory responses; In malignant tumors, lactic acid produced by tumor tissues promotes the polarization of tumor-associated macrophages, which in turn promotes tumor progression. In this review, we examined the relationship between lactic acid and macrophage metabolism. We further discussed how lactic acid plays a role in maintaining the homeostasis of macrophages, as well as the biology of macrophage polarization and the M1/M2 imbalance in human diseases. Potential methods to target lactic acid in the treatment of inflammation and cancer will also be discussed so as to provide new strategies for the treatment of diseases.

ADSC-Exos containing MALAT1 promotes wound healing by targeting miR-124 through activating Wnt/β-catenin pathway

Cutaneous wound is a soft tissue injury that is difficult to heal during aging. It has been demonstrated that adipose-derived stem cells (ADSCs) and its secreted exosomes exert crucial functions in cutaneous wound healing. The present study aimed to elucidate the mechanism of exosomes derived from ADSCs (ADSC-Exos) containing MALAT1 in wound healing. ADSCs were isolated from human normal subcutaneous adipose tissues and identified by flow cytometry analysis. Exosomes were extracted from ADSC supernatants and MALAT1 expression was determined using qRT-PCR analysis. HaCaT and HDF cells were exposed to hydrogen peroxide (H2O2) for simulating the skin lesion model. Subsequently, CCK-8, flow cytometry, wound healing and transwell assays were employed to validate the role of ADSC-Exos containing MALAT1 in the skin lesion model. Besides, cells were transfected with sh-MALAT1 to verify the protective role of MALAT1 in wound healing. The binding relationship between MALAT1 and miR-124 were measured by dual-luciferase reporter assay. ADSC-Exos promoted cell proliferation, migration, and inhibited cell apoptosis of HaCaT and HDF cells impaired by H2O2. However, the depletion of MALAT1 in ADSC-Exos lose these protective effects on HaCaT and HDF cells. Moreover, miR-124 was identified to be a target of MALAT1. Furthermore, ADSC-Exos containing MALAT1 could mediate H2O2-induced wound healing by targeting miR-124 and activating Wnt/β-catenin pathway. ADSC-Exos containing MALAT1 play a positive role in cutaneous wound healing possibly via targeting miR-124 through activating the Wnt/β-catenin pathway, which may provide novel insights into the therapeutic target for cutaneous wound healing.

Prolyl hydroxylase 2 silencing enhances the paracrine effects of mesenchymal stem cells on necrotizing enterocolitis in an NF-κB-dependent mechanism

Treatment options for necrotizing enterocolitis (NEC) remain inadequate. Here we examined if and how prolyl hydroxylase 2 (PHD2) silencing enhances the paracrine effects of bone-marrow-derived mesenchymal stem cells (BM-MSCs) on NEC. In this study, BM-MSCs were transduced with lentiviruses containing GFP (GFP-MSC) or shPHD2-GFP constructs (PHDMSC), followed by intraperitoneal injection of the PHDMSC-conditioned medium (PHDMSC-CM) or the GFP-MSC-conditioned medium (MSC-CM) into a rat pup model of NEC. Our results showed that systemic infusion of PHDMSC-CM, but not MSC-CM, significantly improved intestinal damage and survival of NEC rats. Such benefits may involve the modulation of epithelial regeneration and inflammation, as indicated by the regeneration of intestinal epithelial/stem cells, the regulation of Treg cells function and pro-/anti-inflammatory cytokine balance. The mechanism for the superior paracrine efficacy of PHDMSC is related to a higher release of pivotal factor IGF-1 and TGF-β2. NF-κB activation was induced by PHD2 silencing to induce IGF-1 and TGF-β2 secretion via binding to IGF-1 and TGF-β2 gene promoter. Our work indicated that PHD2 silencing enhanced the paracrine effect of BM-MSCs on NEC via the NF-κB-dependent mechanism which may be a novel strategy for stem cell therapy on NEC.

A review on different methods to increase the efficiency of mesenchymal stem cell-based wound therapy

Mesenchymal stem cells (MSCs) accelerate wound healing but the harsh environment of wound site limits the engraftment, retention, and survival rate of transplanted cells. There are multiple approaches that amplify the therapeutic potential of MSCs. The MSCs derived from medical waste material, provide comparable regenerative abilities compared to traditional sources. The application of different scaffolds increases MSC delivery and migration into the wound. The spheroid culture of MSC increases the paracrine effects of the entrapped cells and the secretion of pro-angiogenic and anti-inflammatory cytokines. The MSC pretreating and preconditioning enhances the cell migration, proliferation, and survival rate, which lead to higher angiogenesis, re-epithelialization, wound closure, and granulation tissue formation. Moreover, genetic modification has been performed in order to increase MSC angiogenesis, differentiation potential, as well as the cell life span. Herein, we review the results of aforementioned approaches and provide information accommodating to the continued development of MSC-based wound therapy in the future.

Adipose mesenchymal stem cell-derived exosomes promote cell proliferation, migration, and inhibit cell apoptosis via Wnt/β-catenin signaling in cutaneous wound healing

Cutaneous wounds, a type of soft tissue injury, are difficult to heal in aging. Differentiation, migration, proliferation, and apoptosis of skin cells are identified as key factors during wound healing processes. Mesenchymal stem cells have been documented as possible candidates for wound healing treatment because their use could augment the regenerative capacity of many tissues. However, the effects of exosomes derived from adipose-derived stem cell (ADSC-exos) on cutaneous wound healing remain to be carefully elucidated. In this present study, HaCaT cells were exposed to hydrogen peroxide (H₂ O ₂ ) for the establishment of the skin lesion model. Cell Counting Kit-8 assay, migration assay, and flow cytometry assay were conducted to detect the biological function of ADSC-exos in skin lesion model. Finally, the possible mechanism was further investigated using Western blot assay. The successful construction of the skin lesion model was confirmed by results of the enhanced cell apoptosis of HaCaT cells induced by H ₂ O ₂ , the increased Bax expression and decreased Bcl-2 expression. CD9 and CD63 expression evidenced the existence of ADSC-exos. The results of functional experiments demonstrated that ADSC-exos could prompt cell proliferation and migration of HaCaT cells, and repress cell apoptosis of HaCaT cells. In addition, the activation of Wnt/β-catenin signaling was confirmed by the enhanced expression of β-catenin at the protein level. Collectively, our findings suggest that ADSC-exos play a positive role in cutaneous wound healing possibly via Wnt/β-catenin signaling. Our study may provide new insights into the therapeutic target for cutaneous wound healing.

Does osteogenic potential of clonal human bone marrow mesenchymal stem/stromal cells correlate with their vascular supportive ability?

BACKGROUND

Human bone marrow-derived mesenchymal stem/stromal cells (hBM MSCs) have multiple functions, critical for skeletal formation and function. Their functional heterogeneity, however, represents a major challenge for their isolation and in developing potency and release assays to predict their functionality prior to transplantation. Additionally, potency, biomarker profiles and defining mechanisms of action in a particular clinical setting are increasing requirements of Regulatory Agencies for release of hBM MSCs as Advanced Therapy Medicinal Products for cellular therapies. Since the healing of bone fractures depends on the coupling of new blood vessel formation with osteogenesis, we hypothesised that a correlation between the osteogenic and vascular supportive potential of individual hBM MSC-derived CFU-F (colony forming unit-fibroblastoid) clones might exist.

METHODS

We tested this by assessing the lineage (i.e. adipogenic (A), osteogenic (O) and/or chondrogenic (C)) potential of individual hBM MSC-derived CFU-F clones and determining if their osteogenic (O) potential correlated with their vascular supportive profile in vitro using lineage differentiation assays, endothelial-hBM MSC vascular co-culture assays and transcriptomic (RNAseq) analyses.

RESULTS

Our results demonstrate that the majority of CFU-F (95%) possessed tri-lineage, bi-lineage or uni-lineage osteogenic capacity, with 64% of the CFU-F exhibiting tri-lineage AOC potential. We found a correlation between the osteogenic and vascular tubule supportive activity of CFU-F clones, with the strength of this association being donor dependent. RNAseq of individual clones defined gene fingerprints relevant to this correlation.

CONCLUSIONS

This study identified a donor-dependent correlation between osteogenic and vascular supportive potential of hBM MSCs and important gene signatures that support these functions that are relevant to their bone regenerative properties.