Cell surface peptidase CD26/dipeptidylpeptidase IV regulates CXCL12/stromal cell-derived factor-1 alpha-mediated chemotaxis of human cord blood CD34+ progenitor cells

The fulfilled promise and unmet potential of umbilical cord blood

PURPOSE OF REVIEW

Here, we review classic and emerging uses of umbilical cord blood and highlight strategies to improve its utility, focusing on selection of the appropriate units and cell types for the intended applications.

RECENT LITERATURE

Recent studies have shown advancements in cord blood cell utility in a variety of cellular therapies and have made strides in elucidating manners to select the best units for therapy and target new ways to improve the various cell subpopulations for their respective applications.

SUMMARY

Umbilical cord blood is a proven source of cells for hematopoietic cell transplantation and research and is an important potential source for additional cellular therapies. However, cord blood utility is limited by low "doses" of potent cells that can be obtained from individual units, a limitation that is specific to cord blood as a donor source. In addition to traditional CD34 + progenitor cells, cord blood lymphocytes are being pursued as therapeutic entities with their own unique properties and characteristics. Thus, selection of ideal units depends on the intended therapeutic entity and target, and identification of differential potency parameters is critical to drive effective banking strategies accommodating successful clinical use of cord blood in broader cell therapy settings.

An emerging paradigm of CXCL12 involvement in the metastatic cascade

The chemokine CXCL12, also known as stromal cell-derived factor 1 (SDF1), has emerged as a pivotal regulator in the intricate molecular networks driving cancer progression. As an influential factor in the tumor microenvironment, CXCL12 plays a multifaceted role that spans beyond its traditional role as a chemokine inducing invasion and metastasis. Indeed, CXCL12 has been assigned functions related to epithelial-to-mesenchymal transition, cancer cell stemness, angiogenesis, and immunosuppression, all of which are currently viewed as specialized biological programs contributing to the "metastatic cascade" among other cancer hallmarks. Its interaction with its cognate receptor, CXCR4, initiates a cascade of events that not only shapes the metastatic potential of tumor cells but also defines the niches within the secondary organs that support metastatic colonization. Given the profound implications of CXCL12 in the metastatic cascade, understanding its mechanistic underpinnings is of paramount importance for the targeted elimination of rate-limiting steps in the metastatic process. This review aims to provide a comprehensive overview of the current knowledge surrounding the role of CXCL12 in cancer metastasis, especially its molecular interactions rationalizing its potential as a therapeutic target.

Proteolytic inactivation of CXCL12 in the lungs and circulation of COVID-19 patients

The human chemokine stromal cell-derived factor-1 (SDF-1) or CXCL12 is involved in several homeostatic processes and pathologies through interaction with its cognate G protein-coupled receptor CXCR4. Recent research has shown that CXCL12 is present in the lungs and circulation of patients with coronavirus disease 2019 (COVID-19). However, the question whether the detected CXCL12 is bioactive was not addressed. Indeed, the activity of CXCL12 is regulated by NH2- and COOH-terminal post-translational proteolysis, which significantly impairs its biological activity. The aim of the present study was to characterize proteolytic processing of CXCL12 in broncho-alveolar lavage (BAL) fluid and blood plasma samples from critically ill COVID-19 patients. Therefore, we optimized immunosorbent tandem mass spectrometry proteoform analysis (ISTAMPA) for detection of CXCL12 proteoforms. In patient samples, this approach uncovered that CXCL12 is rapidly processed by site-specific NH2- and COOH-terminal proteolysis and ultimately degraded. This proteolytic inactivation occurred more rapidly in COVID-19 plasma than in COVID-19 BAL fluids, whereas BAL fluid samples from stable lung transplantation patients and the non-affected lung of lung cancer patients (control groups) hardly induced any processing of CXCL12. In COVID-19 BAL fluids with high proteolytic activity, processing occurred exclusively NH2-terminally and was predominantly mediated by neutrophil elastase. In low proteolytic activity BAL fluid and plasma samples, NH2- and COOH-terminal proteolysis by CD26 and carboxypeptidases were observed. Finally, protease inhibitors already approved for clinical use such as sitagliptin and sivelestat prevented CXCL12 processing and may therefore be of pharmacological interest to prolong CXCL12 half-life and biological activity in vivo.

Dipeptidylpeptidase 4 promotes survival and stemness of acute myeloid leukemia stem cells

Leukemic-stem-cell-specific targeting may improve the survival of patients with acute myeloid leukemia (AML) by avoiding the ablative effects of standard regimens on normal hematopoiesis. Herein, we perform an unbiased screening of compounds targeting cell surface proteins and identify clinically used DPP4 inhibitors as strong suppressors of AML development in both murine AML models and primary human AML cells xenograft model. We find in retrovirus-induced AML mouse models that DPP4-deficient AML cell-transplanted mice exhibit delay and reversal of AML development, whereas deletion of DPP4 has no significant effect on normal hematopoiesis. DPP4 activates and sustains survival of AML stem cells that are critical for AML development in both human and animal models via binding with Src kinase and activation of nuclear factor κB (NF-κB) signaling. Thus, inhibition of DPP4 is a potential therapeutic strategy against AML development through suppression of survival and stemness of AML cells.

DPP4-Truncated CXCL12 Alters CXCR4/ACKR3 Signaling, Osteogenic Cell Differentiation, Migration, and Senescence

Bone marrow skeletal stem cells (SSCs) secrete many cytokines including stromal derived factor-1 or CXCL12, which influences cell proliferation, migration, and differentiation. All CXCL12 splice variants are rapidly truncated on their N-terminus by dipeptidyl peptidase 4 (DPP4). This includes the common variant CXCL12 alpha (1-68) releasing a much less studied metabolite CXCL12(3-68). Here, we found that CXCL12(3-68) significantly inhibited SSC osteogenic differentiation and RAW-264.7 cell osteoclastogenic differentiation and induced a senescent phenotype in SSCs. Importantly, pre-incubation of SSCs with CXCL12(3-68) significantly diminished their ability to migrate toward CXCL12(1-68) in transwell migration assays. Using a high-throughput G-protein-coupled receptor (GPCR) screen (GPCRome) and bioluminescent resonance energy transfer molecular interaction assays, we revealed that CXCL12(3-68) acts via the atypical cytokine receptor 3-mediated β-arrestin recruitment and as a competitive antagonist to CXCR4-mediated signaling. Finally, a reverse phase protein array assay revealed that DPP4-cleaved CXCL12 possesses a different downstream signaling profile from that of intact CXCL12 or controls. The data presented herein provides insights into regulation of CXCL12 signaling. Importantly, it demonstrates that DPP4 proteolysis of CXCL12 generates a metabolite with significantly different and previously overlooked bioactivity that helps explain discrepancies in the literature. This also contributes to an understanding of the molecular mechanisms of osteoporosis and bone fracture repair and could potentially significantly affect the interpretation of experimental outcomes with clinical consequences in other fields where CXCL12 is vital, including cancer biology, immunology, cardiovascular biology, neurobiology, and associated pathologies.

Dipeptidyl peptidase-4 cell surface expression marks an abundant adipose stem/progenitor cell population with high stemness in human white adipose tissue

The capacity of adipose stem/progenitor cells (ASCs) to undergo self-renewal and differentiation is crucial for adipose tissue homoeostasis, regeneration and expansion. However, the heterogeneous ASC populations of the adipose lineage constituting adipose tissue are not precisely known. In the present study, we demonstrate that cell surface expression of dipeptidyl peptidase-4 (DPP4)/cluster of differentiation 26 (CD26) subdivides the DLK1^-/CD34⁺/CD45^-/CD31^- ASC pool of human white adipose tissues (WATs) into two large populations. Ex vivo, DPP4⁺ ASCs possess higher self-renewal and proliferation capacity and lesser adipocyte differentiation potential than DDP4^- ASCs. The knock-down of DPP4 in ASC leads to significantly reduced proliferation and self-renewal capacity, while adipogenic differentiation is increased. Ectopic overexpression of DPP4 strongly inhibits adipogenesis. Moreover, in whole mount stainings of human subcutaneous (s)WAT, we detect DPP4 in CD34⁺ ASC located in the vascular stroma surrounding small blood vessels and in mature adipocytes. We conclude that DPP4 is a functional marker for an abundant ASC population in human WAT with high proliferation and self-renewal potential and low adipogenic differentiation capacity.

Stem cell homing in periodontal tissue regeneration

The destruction of periodontal tissue is a crucial problem faced by oral diseases, such as periodontitis and tooth avulsion. However, regenerating periodontal tissue is a huge clinical challenge because of the structural complexity and the poor self-healing capability of periodontal tissue. Tissue engineering has led to advances in periodontal regeneration, however, the source of exogenous seed cells is still a major obstacle. With the improvement of in situ tissue engineering and the exploration of stem cell niches, the homing of endogenous stem cells may bring promising treatment strategies in the future. In recent years, the applications of endogenous cell homing have been widely reported in clinical tissue repair, periodontal regeneration, and cell therapy prospects. Stimulating strategies have also been widely studied, such as the combination of cytokines and chemokines, and the implantation of tissue-engineered scaffolds. In the future, more research needs to be done to improve the efficiency of endogenous cell homing and expand the range of clinical applications.

Clinical Progress and Preclinical Insights Into Umbilical Cord Blood Transplantation Improvement

The application of umbilical cord blood (UCB) as an important source of hematopoietic stem and progenitor cells (HSPCs) for hematopoietic reconstitution in the clinical context has steadily grown worldwide in the past 30 years. UCB has advantages that include rapid availability of donors, less strict HLA-matching demands, and low rates of graft-versus-host disease (GVHD) versus bone marrow (BM) and mobilized peripheral blood (PB). However, the limited number of HSPCs within a single UCB unit often leads to delayed hematopoietic engraftment, increased risk of transplant-related infection and mortality, and proneness to graft failure, thus hindering wide clinical application. Many strategies have been developed to improve UCB engraftment, most of which are based on 2 approaches: increasing the HSPC number ex vivo before transplantation and enhancing HSPC homing to the recipient BM niche after transplantation. Recently, several methods have shown promising progress in UCB engraftment improvement. Here, we review the current situations of UCB manipulation in preclinical and clinical settings and discuss challenges and future directions.

Refining the migration and engraftment of short-term and long-term HSCs by enhancing homing-specific adhesion mechanisms

In contrast to the short-term(ST)-CD34pos stem cells, studies have suggested that long-term (LT) hematopoietic stem cells (HSC) found in the CD34neg stem cell pool have trouble migrating and engrafting when introduced intravenously. We set out to fully elucidate the adhesion mechanisms used by ST/LT-HSCs to migrate to the bone marrow in order to understand these deficiencies. Focusing on murine ST-HSCs(Flk2negCD34pos) and LT-HSCs(Flk2negCD34neg), we observed a distinctive expression pattern of bone marrow homing effectors necessary for the first step, namely sialyl Lewis-X(sLex;ligand for E-selectin), and the second step, namely CXCR4 (receptor for SDF-1). sLex expression was higher on Flk2negCD34pos ST-HSCs(>60%) compared to Flk2negCD34neg LT-HSCs(<10%), which correlated to binding to E-selectin. Higher levels of CXCR4 were observed on Flk2negCD34pos ST-HSCs compared to Flk2negCD34neg LT-HSCs. Interestingly, expression of CD26, a peptidase known to deactivate chemokines (i.e.SDF-1), was higher on Flk2negCD34neg LT-HSCs. Given that migration is compromised in Flk2negCD34neg LT-HSCs, we aimed to enhance their ability to migrate using recombinant fucosyltransferase 6 (rhFTVI) and DiprotinA (CD26-inhibitor). We observed that although LT-HSCs expressed low levels of sLex, in vivo engraftment was not compromised. Moreover, although both treaments enhanced migration in vitro, only pre-treatment of LT-HSCs with DiprotinA enhanced engraftment in vivo. Remarkably, fucosylation of Flk2negCD34pos ST-HSCs consistently led to their ability to transplant secondary recipients, the gold standard for testing functionality of LT-HSCs. These data suggest that treatments to overcome the molecular disparity in adhesion mechanisms among ST-HSCs and LT-HSCs, differentially influences their abilities to migrate and engraft in vivo and boosts ST-HSCs engraftment in vivo.

Leukemia Inhibitory Factor Promotes Survival of Hematopoietic Progenitors Ex Vivo and Is Post-Translationally Regulated by DPP4

Hematopoietic cells are regulated in part by extracellular cues from cytokines. Leukemia inhibitory factor (LIF) promotes survival, self-renewal, and pluripotency of mouse embryonic stem cells (mESC). While genetic deletion of LIF affects hematopoietic progenitor cells (HPCs), the direct effect of LIF protein exposure on HPC survival is not known. Furthermore, post-translational modifications (PTM) of LIF and their effects on its function have not been evaluated. We demonstrate that treatment with recombinant LIF preserves mouse and human HPC numbers in stressed conditions when growth factor addition is delayed ex vivo. We show that Lif is upregulated in response to irradiation-induced stress. We reveal novel PTM of LIF where it is cleaved twice by dipeptidyl peptidase 4 (DPP4) protease so that it loses its 4 N-terminal amino acids. This truncation of LIF down-modulates LIF's ability to preserve functional HPC numbers ex vivo following delayed growth factor addition. DPP4-truncated LIF blocks the ability of full-length LIF to preserve functional HPC numbers. This LIF role and its novel regulation by DPP4 have important implications for normal and stress hematopoiesis, as well as for other cellular contexts in which LIF and DPP4 are implicated.

The Multiple Biological Functions of Dipeptidyl Peptidase-4 in Bone Metabolism

Dipeptidyl peptidase-4 (DPP4) is a ubiquitously occurring protease involved in various physiological and pathological processes ranging from glucose homeostasis, immunoregulation, inflammation to tumorigenesis. Recently, the benefits of DPP4 inhibitors as novel hypoglycemic agents on bone metabolism have attracted extensive attraction in many studies, indicating that DPP4 inhibitors may regulate bone homeostasis. The effects of DPP4 on bone metabolism are still unclear. This paper thoroughly reviews the potential mechanisms of DPP4 for interaction with adipokines, bone cells, bone immune cells, and cytokines in skeleton system. This literature review shows that the increased DPP4 activity may indirectly promote bone resorption and inhibit bone formation, increasing the risk of osteoporosis. Thus, bone metabolic balance can be improved by decreasing DPP4 activities. The substantial evidence collected and analyzed in this review supports this implication.

Potential Effect of DPP-4 Inhibitors Towards Hepatic Diseases and Associated Glucose Intolerance

Dipeptidyl-peptidase-4 (DPP-4) is an enzyme having various properties and physiological roles in lipid accumulation, resistance to anticancer agents, and immune stimulation. DPP-4 includes membrane-bound peptidases and is a kind of enzyme that cleaves alanine or proline-containing peptides such as incretins, chemokines, and appetite-suppressing hormones (neuropeptide) at their N-terminal dipeptides. DPP-4 plays a role in the final breakdown of peptides produced by other endo and exo-peptidases from nutritious proteins and their absorption in these tissues. DPP-4 enzyme activity has different modes of action on glucose metabolism, hunger regulation, gastrointestinal motility, immune system function, inflammation, and pain regulation. According to the literature survey, as DPP-4 levels increase in individuals with liver conditions, up-regulation of hepatic DPP-4 expression is likely to be the cause of glucose intolerance or insulin resistance. This review majorly focuses on the cleavage of alanine or proline-containing peptides such as incretins by the DPP-4 and its resulting conditions like glucose intolerance and cause of DPP-4 level elevation due to some liver conditions. Thus, we have discussed the various effects of DPP-4 on the liver diseases like hepatitis C, non-alcoholic fatty liver, hepatic regeneration and stem cell, hepatocellular carcinoma, and the impact of elevated DPP-4 levels in association with liver diseases as a cause of glucose intolerance and their treatment drug of choices. In addition, the effect of DPP-4 inhibitors on obesity and their negative aspects are also discussed in brief.

Pleiotropic Benefits of DPP-4 Inhibitors Beyond Glycemic Control

Dipeptidyl peptidase (DPP)-4 inhibitors are oral anti-diabetic medications that block the activity of the ubiquitous enzyme DPP-4. Inhibition of this enzyme increases the level of circulating active glucagon-like peptide (GLP)-1 secreted from L-cells in the small intestine. GLP-1 increases the glucose level, dependent on insulin secretion from pancreatic β-cells; it also decreases the abnormally increased level of glucagon, eventually decreasing the blood glucose level in patients with type 2 diabetes. DPP-4 is involved in many physiological processes other than the degradation of GLP-1. Therefore, the inhibition of DPP-4 may have numerous effects beyond glucose control. In this article, we review the pleiotropic effects of DPP-4 inhibitors beyond glucose control, including their strong beneficial effects on the stress induced accelerated senescence of vascular cells, and the possible clinical implications of these effects.

The Role of Post-Translational Modifications of Chemokines by CD26 in Cancer

Chemokines are a large family of small chemotactic cytokines that fulfill a central function in cancer. Both tumor-promoting and -impeding roles have been ascribed to chemokines, which they exert in a direct or indirect manner. An important post-translational modification that regulates chemokine activity is the NH₂-terminal truncation by peptidases. CD26 is a dipeptidyl peptidase (DPPIV), which typically clips a NH₂-terminal dipeptide from the chemokine. With a certain degree of selectivity in terms of chemokine substrate, CD26 only recognizes chemokines with a penultimate proline or alanine. Chemokines can be protected against CD26 recognition by specific amino acid residues within the chemokine structure, by oligomerization or by binding to cellular glycosaminoglycans (GAGs). Upon truncation, the binding affinity for receptors and GAGs is altered, which influences chemokine function. The consequences of CD26-mediated clipping vary, as unchanged, enhanced, and reduced activities are reported. In tumors, CD26 most likely has the most profound effect on CXCL12 and the interferon (IFN)-inducible CXCR3 ligands, which are converted into receptor antagonists upon truncation. Depending on the tumor type, expression of CD26 is upregulated or downregulated and often results in the preferential generation of the chemokine isoform most favorable for tumor progression. Considering the tight relationship between chemokine sequence and chemokine binding specificity, molecules with the appropriate characteristics can be chemically engineered to provide innovative therapeutic strategies in a cancer setting.

Consequences of coronavirus infections for primitive and mature hematopoietic cells: new insights and why it matters

PURPOSE OF REVIEW

In recent history there have been three outbreaks of betacoronavirus infections in humans, with the most recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; causing Coronavirus disease 2019 [COVID-19]) outbreak leading to over two million deaths, with a rapidly rising death toll. Much remains unknown about host cells and tissues affected by coronavirus infections, including the hematopoietic system. Here, we discuss the recent findings examining effects that coronavirus infection or exposure has on hematopoietic cells and the clinical implications for these effects.

RECENT FINDINGS

Recent studies have centered on SARS-CoV-2, demonstrating that hematopoietic stem and progenitor cells and mature immune cells may be susceptible to infection and are impacted functionally by exposure to SARS-CoV-2 Spike protein. These findings have important implications regarding hematologic complications arising from COVID-19 and other coronavirus-induced disease, which we discuss here.

SUMMARY

Infection with coronaviruses sometimes leads to hematologic complications in patients, and these hematologic complications are associated with poorer prognosis. These hematologic complications may be caused by coronavirus direct infection or impact on primitive hematopoietic cells or mature immune cells, by indirect effects on these cells, or by a combination thereof. It is important to understand how hematologic complications arise in order to seek new treatments to improve patient outcomes.

Combination of a CD26 Inhibitor, G-CSF, and Short-term Immunosuppressants Modulates Allotransplant Survival and Immunoregulation in a Rodent Hindlimb Allotransplant Model

BACKGROUND

Recent studies have demonstrated that inhibition of CD26 potentiates stromal cell-derived factor-1α (SDF-1α), promotes tissue regeneration, and suppresses the rejection of organ transplants. This study investigated whether the combination of a CD26 inhibitor (CD26i) with granulocyte colony-stimulating factor (G-CSF) and short-term immunosuppressants modulates vascularized composite tissue allotransplant survival in a rodent orthotopic hindlimb allotransplant model.

METHODS

The hindlimb allotransplantation from Brown-Norway to Lewis rats was divided into 4 groups. Group 1 (controls) did not receive any treatment. Group 2 was treated with short-term antilymphocyte serum (ALS) and cyclosporine-A (CsA). Group 3 was administrated CD26i and G-CSF. Group 4 received a combination of CD26i/G-CSF/ALS/CsA. Each subgroup comprised 10 rats. Peripheral blood and sampling of transplanted tissues were collected for immunological and histological analysis.

RESULTS

The results revealed that allotransplant survival was found to be significantly prolonged in group 4 with CD26i/G-CSF/ALS/CsA treatment compared with those in the other groups. The interleukin-10 and transforming growth factor-βl levels, the percentage of CD4+/CD25+/FoxP3+ T cells, as well as the levels of SDF-1α expressions were significantly increased in group 4 compared with those in the other groups. Group 4 revealed a statistical increase in the percentage of donor cells (RT1n) expression in the recipient peripheral blood, and the mixed lymphocyte reaction showed hyporesponsiveness of the T cells to donor alloantigens.

CONCLUSION

The combination of CD26i/G-CSF and short-term immunosuppressants prolongs allotransplant survival by inducing immunoregulatory effects and enhancing the percentage of SDF-1α expression. This immunomodulatory approach has great potential as a strategy to increase vascularized composite allotransplantation survival.

Functional inhibition of cancer stemness-related protein DPP4 rescues tyrosine kinase inhibitor resistance in renal cell carcinoma

Tyrosine kinase inhibitors (TKIs) are used as targeted drugs for advanced renal cell carcinoma (RCC), although most cases eventually progress by acquiring resistance. Cancer stemness plays critical roles in tumor aggressiveness and therapeutic resistance, and dipeptidyl peptidase IV (DPP4) has been recently identified as a cancer stemness-related protein. A question arises whether DPP4 contributes to TKI efficacy in RCC. We established patient-derived RCC spheroids and showed that DPP4 expression is associated with stemness-related gene expression. TKI sunitinib resistance was rescued by DPP4 inhibition using sitagliptin or specific siRNAs in RCC cells and tumors. DPP4 expression can be inducible by retinoic acid and repressed by ALDH1A inhibition. Among type 2 diabetes patients with clinical RCC tumors, higher TKI efficacy is observed in those bearing DPP4^high tumors treated with DPP4 inhibitors. This study provides new insights into TKI resistance and drug repositioning of DPP4 inhibitor as a promising strategy for advanced RCC.

An expanded role for dipeptidyl peptidase 4 in cell regulation

PURPOSE OF REVIEW

Dipeptidyl peptidase 4 (DPP4) is a serine protease with diverse regulatory functions in healthy and diseased cells. Much remains unknown about the mechanisms and targets of DPP4. Here we discuss new studies exploring DPP4-mediated cellular regulation, provide an updated list of potential targets of DPP4, and discuss clinical implications of each.

RECENT FINDINGS

Recent studies have sought enhanced efficacy of targeting DPP4's role in regulating hematopoietic stem and progenitor cells for improved clinical application. Further studies have identified DPP4 functions in different cellular compartments and have proposed ways to target this protein in malignancy. These findings, together with an expanded list of putative extracellular, cell surface, and intracellular DPP4 targets, provide insight into new DPP4-mediated cell regulation.

SUMMARY

DPP4 posttranslationally modifies proteins and peptides with essential roles in hematopoietic cell regulation, stem cell transplantation, and malignancy. Targets include secreted signaling factors and may include membrane proteins and transcription factors critical for different hematopoietic functions. Knowing these targets and functions can provide insight into new regulatory roles for DPP4 that may be targeted to enhance transplantation, treat disease, and better understand different regulatory pathways of hematopoiesis.

The role of Dipeptidyl Peptidase-4 in cutaneous disease

Dipeptidyl peptidase-4 (DPP4) is a multifunctional, transmembrane glycoprotein present on the cell surface of various tissues. It is present in multiple molecular forms including cell surface and soluble. The role of DPP4 and its inhibition in cutaneous dermatoses have been a recent point of investigation. DPP4 exerts a notable influence on T-cell biology, the induction of skin-specific lymphocytes, and the homeostasis between regulatory and effector T cells. Moreover, DPP4 interacts with a broad range of molecules, including adenosine deaminase, caveolin-1, CXCR4 receptor, M6P/insulin-like growth factor II-receptor and fibroblast activation protein-α, triggering downstream effects that modulate the immune response, cell adhesion and chemokine activity. DPP4 expression on melanocytes, keratinocytes and fibroblasts further alters cell function and, thus, has crucial implications in cutaneous pathology. As a result, DPP4 plays a significant role in bullous pemphigoid, T helper type 1-like reactions, cutaneous lymphoma, melanoma, wound healing and fibrotic disorders. This review illustrates the multifactorial role of DPP4 expression, regulation, and inhibition in cutaneous diseases.

Dipeptidyl Peptidase IV as a Muscle Myokine

Dipeptidyl peptidase IV (DPP-IV) is a unique serine protease that exists in a membrane bound state and in a soluble state in most tissues in the body. DPP-IV has multiple targets including cytokines, neuropeptides, and incretin hormones, and plays an important role in health and disease. Recent work suggests that skeletal muscle releases DPP-IV as a myokine and participates in control of muscle blood flow. However, few of the functions of DPP-IV as a myokine have been investigated to date and there is a poor understanding about what causes DPP-IV to be released from muscle.

Regimen-dependent synergism and antagonism of treprostinil and vildagliptin in hematopoietic cell transplantation

The cell dose in umbilical cord blood units is a major determinant for the outcome of hematopoietic cell transplantation. Prostaglandin analogs and dipeptidylpeptidase-4 (DPP4/CD26)-inhibitors enhance the ability of hematopoietic stem cells (HSCs) to reconstitute hematopoiesis. Here we explored the synergism between treprostinil, a stable prostaglandin agonist, and the DPP4/CD26-inhibitor vildagliptin. The combination of treprostinil and forskolin caused a modest but statistically significant increase in the surface levels of DPP4/CD26 on hematopoietic stem and progenitor cells (HSPCs) derived from murine bone and human cord blood. Their migration towards stromal cell-derived factor-1 (SDF-1/CXCL12) was enhanced, if they were pretreated with treprostinil and forskolin, and further augmented by vildagliptin. Administration of vildagliptin rescued 25% of lethally irradiated recipient mice injected with a limiting number of untreated HSPCs, but 90 to 100% of recipients injected with HSPCs preincubated with treprostinil and forskolin. The efficacy of vildagliptin surpassed that of treprostinil (60% rescue). Surprisingly, concomitant administration of vildagliptin and treprostinil resulted in poor survival of recipients indicating mutual antagonism, which was recapitulated when homing of and colony formation by HSPCs were assessed. These observations of regimen-dependent synergism and antagonism of treprostinil and vildagliptin are of translational relevance for the design of clinical trials. KEY MESSAGES: Pretreatment with treprostinil increases surface levels of DPP4/CD26 in HSPCs. Vildagliptin enhances in vitro migration of pretreated HSPCs. Vildagliptin enhances in vivo homing and engraftment of pretreated HSPCs. Unexpected mutual antagonism in vivo by concomitant administration of vildagliptin and treprostinil.

Clinical Advancement and Challenges of ex vivo Expansion of Human Cord Blood Cells

Apart from peripheral blood stem cell (PBSC), umbilical cord blood (UCB) is now a recognized source of stem cells for transplantation. UCB is an especially important source of stem cells for minority populations, which would otherwise be unable to find appropriately matched adult donors. UCB has fewer mature T lymphocytes compared with peripheral blood, thus making a UCB transplantation (UCBT) with a greater degree of HLA mismatch possible. The limited cell dose per UCB sample is however associated with delayed engraftment and a higher risk of graft failure, especially in adult recipients. This lower cell dose can be optimized by performing double unit UCBT, ex vivo UCB expansion prior to transplant and enhancement of the capabilities of the stem cells to home to the bone marrow. UCB contains naïve and immature T cells, thus posing significant challenges with increased risk of infections, graft versus host diseases (GVHD) and relapse following UCBT. Cell engineering techniques have been developed to circumnavigate the immaturity of the T cells, and include virus-specific cytotoxic T cells (VSTs), T cells transduced with disease-specific chimeric antigen receptor (CAR T cells) and regulatory T cell (Tregs) engineering. In this article, we review the advances in UCB ex vivo expansion and engineering to improve engraftment and reduce complications. As further research continues to find ways to overcome the current challenges, outcomes from UCBT will likely improve.

Past, present, and future efforts to enhance the efficacy of cord blood hematopoietic cell transplantation

Cord blood (CB) has been used as a viable source of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) in over 35,000 clinical hematopoietic cell transplantation (HCT) efforts to treat the same variety of malignant and non-malignant disorders treated by bone marrow (BM) and mobilized peripheral blood (mPB) using HLA-matched or partially HLA-disparate related or unrelated donor cells for adult and children recipients. This review documents the beginning of this clinical effort that started in the 1980’s, the pros and cons of CB HCT compared to BM and mPB HCT, and recent experimental and clinical efforts to enhance the efficacy of CB HCT. These efforts include means for increasing HSC numbers in single CB collections, expanding functional HSCs ex vivo, and improving CB HSC homing and engraftment, all with the goal of clinical translation. Concluding remarks highlight the need for phase I/II clinical trials to test the experimental procedures that are described, either alone or in combination.

CD26 and Asthma: a Comprehensive Review

Asthma is a heterogeneous and chronic inflammatory family of disorders of the airways with increasing prevalence that results in recurrent and reversible bronchial obstruction and expiratory airflow limitation. These diseases arise from the interaction between environmental and genetic factors, which collaborate to cause increased susceptibility and severity. Many asthma susceptibility genes are linked to the immune system or encode enzymes like metalloproteases (e.g., ADAM-33) or serine proteases. The S9 family of serine proteases (prolyl oligopeptidases) is capable to process peptide bonds adjacent to proline, a kind of cleavage-resistant peptide bonds present in many growth factors, chemokines or cytokines that are important for asthma. Curiously, two serine proteases within the S9 family encoded by genes located on chromosome 2 appear to have a role in asthma: CD26/dipeptidyl peptidase 4 (DPP4) and DPP10. The aim of this review is to summarize the current knowledge about CD26 and to provide a structured overview of the numerous functions and implications that this versatile enzyme could have in this disease, especially after the detection of some secondary effects (e.g., viral nasopharyngitis) in type II diabetes mellitus patients (a subset with a certain risk of developing obesity-related asthma) upon CD26 inhibitory therapy.

Pegfilgrastim and linagliptin potentiate chemoattraction of Ccr2 and Cd44 stem cells accompanied by alterations of cardiac Hgf, Igf-1 and Mcp-1 in daunorubicin cardiomyopathy

Objective

Daunorubicin (DAU) downregulates cytokines promoting stem cell migration and homing into the heart, reducing cardiac regeneration after anticancer chemotherapy. Pegfilgrastim (PFIL) protects from DAU-induced neutropenia but its cardioprotective potential remains unclear. We tested whether pegfilgrastim and a dipeptidyl peptidase-4 inhibitor linagliptin, potential enhancers of stem cells migration and homing, would improve DAU-cardiomyopathy.

Methods

DAU (7.5 mg/kg, i.v.) was administered to male Wistar rats to induce cardiotoxicity. Pegfilgrastim (100 µg/kg, s.c.) was administered 24h after DAU, and linagliptin was administered orally for 8 weeks (5 mg/kg/day, LINA). Cardiac damage markers (Nppa, Myh6, Myh7, Gp91phox), cytokines (Sdf-1alpha, Mcp-1, Vegf, Hgf, Igf-1), stem cell markers (Cxcr4, Ccr2, Cd34, Cd133, Cd44, Cd105) were determined by qRT-PCR.

Key findings

Decreased Myh6, elevated Myh7 Nppa, and Gp91phox were not ameliorated by PFIL + LINA. Downregulated expressions of cytokines (Vegf, Sdf-1alpha) and stem cells markers (Cxcr4, Cd34, Cd133, and Cd105) remained decreased after PFIL + LINA. DAU-induced upregulation of Mcp-1, Ccr2 and Cd44 was further potentiated by PFIL + LINA. PFIL + LINA normalised expression of Hgf and Igf-1.

Conclusions

Although PFIL + LINA failed in universal potentiation of stem cells migration and homing, the expression of stem cell markers Ccr2 and Cd44 in the heart potentially increased through the preservation of Hgf, Igf-1 and upregulation of Mcp-1.

CXCL12 and Its Isoforms: Different Roles in Pancreatic Cancer?

CXCL12 is a chemokine that acts through CXCR4 and ACKR3 receptors and plays a physiological role in embryogenesis and haematopoiesis. It has an important role also in tumor development, since it is released by stromal cells of tumor microenvironment and alters the behavior of cancer cells. Many studies investigated the roles of CXCL12 in order to understand if it has an anti- or protumor role. In particular, it seems to promote tumor invasion, proliferation, angiogenesis, epithelial to mesenchymal transition (EMT), and metastasis in pancreatic cancer. Nevertheless, some evidence shows opposite functions; therefore research on CXCL12 is still ongoing. These discrepancies could be due to the presence of at least six CXCL12 splicing isoforms, each with different roles. Interestingly, three out of six variants have the highest levels of expression in the pancreas. Here, we report the current knowledge about the functions of this chemokine and then focus on pancreatic cancer. Moreover, we discuss the methods applied in recent studies in order to understand if they took into account the existence of the CXCL12 isoforms.

What doesn't kill you makes you stranger: Dipeptidyl peptidase-4 (CD26) proteolysis differentially modulates the activity of many peptide hormones and cytokines generating novel cryptic bioactive ligands

Dipeptidyl peptidase 4 (DPP4) is an exopeptidase found either on cell surfaces where it is highly regulated in terms of its expression and surface availability (CD26) or in a free/circulating soluble constitutively available and intrinsically active form. It is responsible for proteolytic cleavage of many peptide substrates. In this review we discuss the idea that DPP4-cleaved peptides are not necessarily inactivated, but rather can possess either a modified receptor selectivity, modified bioactivity, new antagonistic activity, or even a novel activity relative to the intact parent ligand. We examine in detail five different major DPP4 substrates: glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), peptide tyrosine-tyrosine (PYY), and neuropeptide Y (NPY), and stromal derived factor 1 (SDF-1 aka CXCL12). We note that discussion of the cleaved forms of these five peptides are underrepresented in the research literature, and are both poorly investigated and poorly understood, representing a serious research literature gap. We believe they are understudied and misinterpreted as inactive due to several factors. This includes lack of accurate and specific quantification methods, sample collection techniques that are inherently inaccurate and inappropriate, and a general perception that DPP4 cleavage inactivates its ligand substrates. Increasing evidence points towards many DPP4-cleaved ligands having their own bioactivity. For example, GLP-1 can work through a different receptor than GLP-1R, DPP4-cleaved GIP can function as a GIP receptor antagonist at high doses, and DPP4-cleaved PYY, NPY, and CXCL12 can have different receptor selectivity, or can bind novel, previously unrecognized receptors to their intact ligands, resulting in altered signaling and functionality. We believe that more rigorous research in this area could lead to a better understanding of DPP4's role and the biological importance of the generation of novel cryptic ligands. This will also significantly impact our understanding of the clinical effects and side effects of DPP4-inhibitors as a class of anti-diabetic drugs that potentially have an expanding clinical relevance. This will be specifically relevant in targeting DPP4 substrate ligands involved in a variety of other major clinical acute and chronic injury/disease areas including inflammation, immunology, cardiology, stroke, musculoskeletal disease and injury, as well as cancer biology and tissue maintenance in aging.

Secreted nuclear protein DEK regulates hematopoiesis through CXCR2 signaling

The nuclear protein DEK is an endogenous DNA-binding chromatin factor regulating hematopoiesis. DEK is one of only 2 known secreted nuclear chromatin factors, but whether and how extracellular DEK regulates hematopoiesis is not known. We demonstrated that extracellular DEK greatly enhanced ex vivo expansion of cytokine-stimulated human and mouse hematopoietic stem cells (HSCs) and regulated HSC and hematopoietic progenitor cell (HPC) numbers in vivo and in vitro as determined both phenotypically (by flow cytometry) and functionally (through transplantation and colony formation assays). Recombinant DEK increased long-term HSC numbers and decreased HPC numbers through a mechanism mediated by the CXC chemokine receptor CXCR2 and heparan sulfate proteoglycans (HSPGs) (as determined utilizing Cxcr2-/- mice, blocking CXCR2 antibodies, and 3 different HSPG inhibitors) that was associated with enhanced phosphorylation of ERK1/2, AKT, and p38 MAPK. To determine whether extracellular DEK required nuclear function to regulate hematopoiesis, we utilized 2 mutant forms of DEK: one that lacked its nuclear translocation signal and one that lacked DNA-binding ability. Both altered HSC and HPC numbers in vivo or in vitro, suggesting the nuclear function of DEK is not required. Thus, DEK acts as a hematopoietic cytokine, with the potential for clinical applicability.

Cord blood research, banking, and transplantation: achievements, challenges, and perspectives

The first hematopoietic transplant in which umbilical cord blood (UCB) was used as the source of hematopoietic cells was performed in October 1988. Since then, significant achievements have been reported in terms of our understanding of the biology of UCB-derived hematopoietic stem (HSCs) and progenitor (HPCs) cells. Over 40,000 UCB transplants (UCBTs) have been performed, in both children and adults, for the treatment of many different diseases, including hematologic, metabolic, immunologic, neoplastic, and neurologic disorders. In addition, cord blood banking has been developed to the point that around 800,000 units are being stored in public banks and more than 4 million units in private banks worldwide. During these 30 years, research in the UCB field has transformed the hematopoietic transplantation arena. Today, scientific and clinical teams are still working on different ways to improve and expand the use of UCB cells. A major effort has been focused on enhancing engraftment to potentially reduce risk of infection and cost. To that end, we have to understand in detail the molecular mechanisms controlling stem cell self-renewal that may lead to the development of ex vivo systems for HSCs expansion, characterize the mechanisms regulating the homing of HSCs and HPCs, and determine the relative place of UCBTs, as compared to other sources. These challenges will be met by encouraging innovative research on the basic biology of HSCs and HPCs, developing novel clinical trials, and improving UCB banking both in the public and private arenas.

Small molecule inhibition of dipeptidyl peptidase-4 enhances bone marrow progenitor cell function and angiogenesis in diabetic wounds

In diabetes, stromal cell-derived factor-1 (SDF-1) expression and progenitor cell recruitment are reduced. Dipeptidyl peptidase-4 (DPP-4) inhibits SDF-1 expression and progenitor cell recruitment. Here we examined the impact of the DPP-4 inhibitor, MK0626, on progenitor cell kinetics in the context of wound healing. Wildtype (WT) murine fibroblasts cultured under high-glucose to reproduce a diabetic microenvironment were exposed to MK0626, glipizide, or no treatment, and SDF-1 expression was measured with ELISA. Diabetic mice received MK0626, glipizide, or no treatment for 6 weeks and then were wounded. Immunohistochemistry was used to quantify neovascularization and SDF-1 expression. Gene expression was measured at the RNA and protein level using quantitative polymerase chain reaction and ELISA, respectively. Flow cytometry was used to characterize bone marrow-derived mesenchymal progenitor cell (BM-MPC) population recruitment to wounds. BM-MPC gene expression was assayed using microfluidic single cell analysis. WT murine fibroblasts exposed to MK0626 demonstrated increased SDF-1 expression. MK0626 treatment significantly accelerated wound healing and increased wound vascularity, SDF-1 expression, and dermal thickness in diabetic wounds. MK0626 treatment increased the number of BM-MPCs present in bone marrow and in diabetic wounds. MK0626 had no effect on BM-MPC population dynamics. BM-MPCs harvested from MK0626-treated mice exhibited increased chemotaxis in response to SDF-1 when compared to diabetic controls. Treatment with a DPP-4 inhibitor significantly improved wound healing, angiogenesis, and endogenous progenitor cell recruitment in the setting of diabetes.

Peripheral blood stem cell mobilization; a look ahead

THE PURPOSE OF REVIEW

Mobilized peripheral blood is the predominant source of stem and progenitor cells for hematologic transplantation. Successful transplant requires sufficient stem cells of high enough quality to recapitulate lifelong hematopoiesis, but in some patients and normal donors, reaching critical threshold stem cell numbers are difficult to achieve. Novel strategies, particularly those offering rapid mobilization and reduced costs, remains an area of interest.This review summarizes critical scientific underpinnings in understanding the process of stem cell mobilization, with a focus on new or improved strategies for their efficient collection and engraftment.

RECENT FINDINGS

Studies are described that provide new insights into the complexity of stem cell mobilization. Agents that target new pathways such HSC egress, identify strategies to collect more potent competing HSC and new methods to optimize stem cell collection and engraftment are being evaluated.

SUMMARY

Agents and more effective strategies that directly address the current shortcomings of hematopoietic stem cell mobilization and transplantation and offer the potential to facilitate collection and expand use of mobilized stem cells have been identified.

Enhancement of stem cell engraftment on a WHIM

WHIM (warts, hypogammaglobulinemia, infections, and myelokathexis) syndrome is a genetic autoimmune disorder that results from gain-of-function mutations in the gene encoding chemokine receptor CXCR4. A previous study characterized a patient with WHIM who underwent a chromothriptic event that resulted in spontaneous deletion of the WHIM allele in a single hematopoietic stem cell and subsequent cure of the disease. In this issue of the JCI, Gao et al. extend this work and show that Cxcl4-haplosufficient bone marrow has a selective advantage for long-term engraftment in murine WHIM models. Moreover, successful engraftment occurred without prior conditioning of recipients. Together, these results have important implications for improving hematopoietic stem/progenitor cell transplant not only for patients with WHIM but also for all patients who may require the procedure.

The pleiotropic cardiovascular effects of dipeptidyl peptidase-4 inhibitors

Patients with Type 2 diabetes have an excess risk for cardiovascular disease. One of the several approaches, included in the guidelines for the management of Type 2 diabetes, is based on dipeptidyl peptidase 4 (DPP-4; also termed CD26) inhibitors, also called gliptins. Gliptins inhibit the degradation of glucagon-like peptide-1 (GLP-1): this effect is associated with increased circulating insulin-to-glucagon ratio, and a consequent reduction of HbA1c. In addition to incretin hormones, there are several proteins that may be affected by DPP-4 and its inhibition: among these some are relevant for the cardiovascular system homeostasis such as SDF-1α and its receptor CXCR4, brain natriuretic peptides, neuropeptide Y and peptide YY. In this review, we will discuss the pathophysiological relevance of gliptin pleiotropism and its translational potential.

Repopulating hematopoietic stem cells from steady-state blood before and after ex vivo culture are enriched in the CD34+CD133+CXCR4low fraction

The feasibility of ex vivo expansion allows us to consider the steady-state peripheral blood as an alternative source of hematopoietic stem progenitor cells for transplantation when growth factor-induced cell mobilization is contraindicated or inapplicable. Ex vivo expansion dramatically enhances the in vivo reconstituting cell population from steady-state blood. In order to investigate phenotype and the expression of homing molecules, the expression of CD34, CD133, CD90, CD45RA, CD26 and CD9 was determined on sorted CD34⁺ cells according to CXCR4 (“neg”, “low” “bright”) and CD133 expression before and after ex vivo expansion. Hematopoietic stem cell activity was determined in vivo on the basis of hematopoietic repopulation of primary and secondary recipients - NSG immuno-deficient mice. In vivo reconstituting cells in the steady-state blood CD34⁺ cell fraction before expansion belong to the CD133⁺ population and are CXCR4^low or, to a lesser extent, CXCR4^neg, while after ex vivo expansion they are contained only in the CD133⁺CXCR4^low cells. The failure of the CXCR4^bright population to engraft is probably due to the exclusive expression of CD26 by these cells. The limiting-dilution analysis showed that both repopulating cell number and individual proliferative capacity were enhanced by ex vivo expansion. Thus, steady-state peripheral blood cells exhibit a different phenotype compared to mobilized and cord blood cells, as well as to those issued from the bone marrow. These data represent the first phenotypic characterization of steady-state blood cells exhibiting short- and long-term hematopoietic reconstituting potential, which can be expanded ex vivo, a sine qua non for their subsequent use for transplantation.

Hippo Signaling Plays an Essential Role in Cell State Transitions during Cardiac Fibroblast Development

During development, progenitors progress through transition states. The cardiac epicardium contains progenitors of essential non-cardiomyocytes. The Hippo pathway, a kinase cascade that inhibits the Yap transcriptional co-factor, controls organ size in developing hearts. Here, we investigated Hippo kinases Lats1 and Lats2 in epicardial diversification. Epicardial-specific deletion of Lats1/2 was embryonic lethal, and mutant embryos had defective coronary vasculature remodeling. Single-cell RNA sequencing revealed that Lats1/2 mutant cells failed to activate fibroblast differentiation but remained in an intermediate cell state with both epicardial and fibroblast characteristics. Lats1/2 mutant cells displayed an arrested developmental trajectory with persistence of epicardial markers and expanded expression of Yap targets Dhrs3, an inhibitor of retinoic acid synthesis, and Dpp4, a protease that modulates extracellular matrix (ECM) composition. Genetic and pharmacologic manipulation revealed that Yap inhibits fibroblast differentiation, prolonging a subepicardial-like cell state, and promotes expression of matricellular factors, such as Dpp4, that define ECM characteristics.

Allogeneic bone marrow transplant in the absence of cytoreductive conditioning rescues mice with β-thalassemia major

β-thalassemia is a group of inherited blood disorders that result in defects in β-globin chain production. Cooley anemia (CA), or β-thalassemia major, is the most severe form of the disease and occurs when an individual has mutations in both copies of the adult β-globin gene. Patients with CA fail to make adult hemoglobin, exhibit ineffective erythropoiesis, experience severe anemia, and are transfusion dependent for life. Currently, allogeneic bone marrow transplantation (BMT) is the only cure; however, few patients have suitable donors for this procedure, which has significant morbidity and mortality. In this study, a novel humanized murine model of CA is rescued from lethal anemia by allogeneic BMT in the absence of cytoreductive conditioning. A single intravenous postnatal injection of allogeneic bone marrow results in stable, mixed hematopoietic chimerism. Five months after transplantation, donor cells accounted for approximately 90% of circulating erythrocytes and up to 15% of hematopoietic stem and progenitor cells. Transplanted mice are transfusion independent, have marked improvement of hematological indices, exhibit no growth retardation or signs of graft-versus-host disease, and are fertile. This study describes a method for the consistent engraftment of allogeneic donor hematopoietic cells that rescues a humanized mouse model of CA from lethal anemia, all in the absence of toxic cytoreductive conditioning.

High-dose sitagliptin for systemic inhibition of dipeptidylpeptidase-4 to enhance engraftment of single cord umbilical cord blood transplantation

Delayed engraftment remains a limitation of umbilical cord blood (UCB) transplantation. We previously showed that inhibition of dipeptidylpeptidase (DPP)-4 using sitagliptin 600 mg daily was safe with encouraging results on engraftment, but inhibition was not sustained. We evaluated the efficacy and feasibility of higher doses of sitagliptin to enhance engraftment of UCB in patients with hematological cancers. Fifteen patients, median age 41 (range, 18-59) years, received single UCB grafts matched at 4 (n=11) or 5 (n=4) of 6 HLA loci with median nucleated cell dose of 3.5 (range, 2.57-4.57) x10⁷/kg. Sitagliptin 600 mg every 12 hours was administered days -1 to +2. All patients engrafted by day 30, with 12 (80%) engrafting by day 21. The median time to neutrophil engraftment was 19 (range, 12-30) days. Plasma DPP-4 activity was better inhibited with a mean residual trough DPP-4 activity of 70%±19%. Compared to patients previously treated with 600 mg/day, sitagliptin 600 mg every 12 hours appeared to improve engraftment, supporting the hypothesis that more sustained DPP-4 inhibition is required. In-vivo inhibition of DPP-4 using high-dose sitagliptin compares favorably with other approaches to enhance UCB engraftment with greater simplicity, and may show synergy in combination with other strategies.

Neuropeptide Y regulates a vascular gateway for hematopoietic stem and progenitor cells

Endothelial cells (ECs) are components of the hematopoietic microenvironment and regulate hematopoietic stem and progenitor cell (HSPC) homeostasis. Cytokine treatments that cause HSPC trafficking to peripheral blood are associated with an increase in dipeptidylpeptidase 4/CD26 (DPP4/CD26), an enzyme that truncates the neurotransmitter neuropeptide Y (NPY). Here, we show that enzymatically altered NPY signaling in ECs caused reduced VE-cadherin and CD31 expression along EC junctions, resulting in increased vascular permeability and HSPC egress. Moreover, selective NPY2 and NPY5 receptor antagonists restored vascular integrity and limited HSPC mobilization, demonstrating that the enzymatically controlled vascular gateway specifically opens by cleavage of NPY by CD26 signaling via NPY2 and NPY5 receptors. Mice lacking CD26 or NPY exhibited impaired HSPC trafficking that was restored by treatment with truncated NPY. Thus, our results point to ECs as gatekeepers of HSPC trafficking and identify a CD26-mediated NPY axis that has potential as a pharmacologic target to regulate hematopoietic trafficking in homeostatic and stress conditions.

The unique structural and functional features of CXCL12

The CXC chemokine CXCL12 is an important factor in physiological and pathological processes, including embryogenesis, hematopoiesis, angiogenesis and inflammation, because it activates and/or induces migration of hematopoietic progenitor and stem cells, endothelial cells and most leukocytes. Therefore, CXCL12 activity is tightly regulated at multiple levels. CXCL12 has the unique property of existing in six splice variants in humans, each having a specific tissue distribution and in vivo activity. Controlled splice variant transcription and mRNA stability determine the CXCL12 expression profile. CXCL12 fulfills its functions in homeostatic and pathological conditions by interacting with its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) and by binding to glycosaminoglycans (GAGs) in tissues and on the endothelium to allow a proper presentation to passing leukocytes. Homodimerizaton and heterodimerization of CXCL12 and its receptors can alter their signaling activity, as exemplified by the synergy between CXCL12 and other chemokines in leukocyte migration assays. Receptor binding may also initiate CXCL12 internalization and its subsequent removal from the environment. Furthermore, CXCL12 activity is regulated by posttranslational modifications. Proteolytic removal of NH₂- or COOH-terminal amino acids, citrullination of arginine residues by peptidyl arginine deiminases or nitration of tyrosine residues reduce CXCL12 activity. This review summarizes the interactions of CXCL12 with the cellular environment and discusses the different levels of CXCL12 activity regulation.

Engineering cord blood to improve engraftment after cord blood transplant

Umbilical cord blood transplant (CBT) has traditionally been associated with slower engraftment of neutrophils, delayed immune reconstitution and consequently higher risk of infections as compared with peripheral blood progenitor cell (PBPC) or bone marrow (BM) transplants. This is primarily due to low numbers of total nucleated cells (TNCs) and the naive nature of CB immune cells. The use of double unit CB transplant (DCBT) increases the total cell dose in the graft, but it still does not produce as rapid engraftment as seen with PBPC or even BM transplants. Herein, we discuss strategies to improve engraftment after CBT. We describe methods of (I) expansion of CB graft ex vivo to increase the total cell dose; and (II) enhancement of BM homing capability of CB progenitor cells; (III) ex vivo expansion of CB derived T cells for improving T cell function against viruses, tumors and protection from graft versus host disease (GVHD). With these novel approaches, engraftment after CBT is now reaching levels comparable to that of other graft types.

Regulation and roles of CD26/DPPIV in hematopoiesis and diseases

Dipeptidyl peptidase IV (DPPIV),¹ on the surface of certain cells, where it is also referred to as CD26, is involved in a vast majority of biological and pathological processes. CD26/DPPIV function contributes to cancer and tumor metastasis as well as inhibition of its expression which alters the expression of immune response-related genes. CD26/DPPIV is a widely distributed multifunctional integral membrane and secreted protein that is defined as early predictive biomarker in HIV, cancer and autoimmunity diseases like diabetes and multiple sclerosis. CD26/DPPIV-chemokine interaction may have a functional role in T-cells and overall immune function. It is expressed at low density on resting T cells, but is upregulated with T cell activation. In this review, we summarize valuable information about detailed biological aspects and pharmacokinetic characteristics of CD26/DPPIV and its clinical efficacy, focusing particularly on the role of CD26/DPPIV in immunological and non-immunological diseases. We also describe our recent work about umbilical cord blood (UCB)² hematopoietic stem cell transplantation strategies in which identified CD26+ cells can be differentiated to immune cells under certain culture condition.

DPP4 truncated GM-CSF and IL-3 manifest distinct receptor-binding and regulatory functions compared with their full-length forms

Dipeptidylpeptidase 4 (DPP4/CD26) enzymatically cleaves select penultimate amino acids of proteins, including colony stimulating factors (CSFs), and has been implicated in cellular regulation. To better understand the role of DPP4 regulation of hematopoiesis, we analyzed the activity of DPP4 on the surface of immature blood cells and then comparatively assessed the interactions and functional effects of full-length (FL) and DPP4 truncated factors [(T)-GM-CSF and- IL-3] on both in vitro and in vivo models of normal and leukemic cells. T-GM-CSF and T-IL-3 had enhanced receptor binding, but decreased CSF activity, compared to their FL forms. Importantly, T-GM-CSF and T-IL-3 significantly, and reciprocally, blunted receptor binding and myeloid progenitor cell proliferation activity of both FL-GM-CSF and FL-IL-3 in vitro and in vivo. Similar effects were apparent in vitro using cluster forming cells from patients with Acute Myeloid Leukemia (AML) regardless of cytogenetic or molecular alterations and in vivo utilizing animal models of leukemia. This suggests that DPP4 T-molecules have modified binding and functions compared to their FL counterparts and may serve regulatory roles in normal and malignant hematopoiesis.

Dipeptidyl Peptidase-IV Inhibition for the Treatment of Cardiovascular Disease - Recent Insights Focusing on Angiogenesis and Neovascularization

Dipeptidyl peptidase IV (DPP-IV) is a complex enzyme that acts as a membrane-anchored cell surface exopeptidase and transmits intracellular signals through a small intracellular tail. DPP-IV exists in human blood in a soluble form, and truncates a large number of peptide hormones, chemokines, cytokines, and growth factors in vitro and in vivo. DPP-IV has gained considerable interest as a therapeutic target, and a variety of DPP-IV inhibitors that prolong the insulinotropic effects of glucagon-like peptide-1 (GLP-1) are widely used in clinical settings as antidiabetic drugs. Indeed, DPP-IV is upregulated in proinflammatory states, including obesity and cardiovascular disease with and without diabetes mellitus. Consistent with this maladaptive role, DPP-IV inhibitors seem to exert a protective role in cardiovascular disease. In addition to their GLP-1-dependent vascular protective actions, DPP-IV inhibitors exhibit GLP-1-independent beneficial effects on angiogenesis/neovascularization via several signaling pathways (e.g., stromal cell-derived factor-1α/C-X-C chemokine receptor type-4, vascular endothelial growth factor-A/endothelial nitric oxide synthase, etc.). This review focuses on recent findings in this field, highlighting the role of DPP-IV in therapeutic angiogenesis/neovascularization in ischemic heart disease and peripheral artery disease.

Truncation of CXCL12 by CD26 reduces its CXC chemokine receptor 4- and atypical chemokine receptor 3-dependent activity on endothelial cells and lymphocytes

The chemokine CXCL12 or stromal cell-derived factor 1/SDF-1 attracts hematopoietic progenitor cells and mature leukocytes through the G protein-coupled CXC chemokine receptor 4 (CXCR4). In addition, it interacts with atypical chemokine receptor 3 (ACKR3 or CXCR7) and glycosaminoglycans. CXCL12 activity is regulated through posttranslational cleavage by CD26/dipeptidyl peptidase 4 that removes two NH₂-terminal amino acids. CD26-truncated CXCL12 does not induce calcium signaling or chemotaxis of mononuclear cells. CXCL12(3-68) was chemically synthesized de novo for detailed biological characterization. Compared to unmodified CXCL12, CXCL12(3-68) was no longer able to signal through CXCR4 via inositol trisphosphate (IP₃), Akt or extracellular signal-regulated kinases 1 and 2 (ERK1/2). Interestingly, the recruitment of β-arrestin 2 to the cell membrane via CXCR4 by CXCL12(3-68) was abolished, whereas a weakened but significant β-arrestin recruitment remained via ACKR3. CXCL12-induced endothelial cell migration and signal transduction was completely abrogated by CD26. Intact CXCL12 hardly induced lymphocyte migration upon intra-articular injection in mice. In contrast, oral treatment of mice with the CD26 inhibitor sitagliptin reduced CD26 activity and CXCL12 cleavage in blood plasma. The potential of CXCL12 to induce intra-articular lymphocyte infiltration was significantly increased in sitagliptin-treated mice and CXCL12(3-68) failed to induce migration under both CD26-inhibiting and non-inhibiting conditions. In conclusion, CD26-cleavage skews CXCL12 towards β-arrestin dependent recruitment through ACKR3 and destroys the CXCR4-mediated lymphocyte chemoattractant properties of CXCL12 in vivo. Hence, pharmacological CD26-blockade in tissues may enhance CXCL12-induced inflammation.

Regulation of Dipeptidyl Peptidase IV in the Post-stroke Rat Brain and In Vitro Ischemia: Implications for Chemokine-Mediated Neural Progenitor Cell Migration and Angiogenesis

Cerebral ischemia evokes abnormal release of proteases in the brain microenvironment that spatiotemporally impact angio-neurogenesis. Dipeptidyl peptidase IV (DPPIV), a cell surface and secreted protease, has been implicated in extracellular matrix remodeling by regulating cell adhesion, migration, and angiogenesis through modifying the functions of the major chemokine stromal-derived factor, SDF1. To elucidate the possible association of DPPIV in ischemic brain, we examined the expression of DPPIV in the post-stroke rat brain and under in vitro ischemia by oxygen glucose deprivation (OGD). We further investigated the effects of DPPIV on SDF1 mediated in vitro chemotactic and angiogenic functions. DPPIV protein and mRNA levels were significantly upregulated during repair phase in the ischemic cortex of the rat brain, specifically in neurons, astrocytes, and endothelial cells. In vitro exposure of Neuro-2a neuronal cells and rat brain endothelial cells to OGD resulted in upregulation of DPPIV. In vitro functional analysis showed that DPPIV decreases the SDF1-mediated angiogenic potential of rat brain endothelial cells and inhibits the migration of Neuro-2a and neural progenitor cells. Western blot analyses revealed decreased levels of phosphorylated ERK1/2 and AKT in the presence of DPPIV. DPPIV inhibitor restored the effects of SDF1. Proteome profile array screening further revealed that DPPIV decreases matrix metalloproteinase-9, a key downstream effector of ERK-AKT signaling pathways. Overall, delayed induction of DPPIV in response to ischemia/reperfusion suggests that DPPIV may play an important role in endogenous brain tissue remodeling and repair processes. This may be mediated through modulation of SDF1-mediated cell migration and angiogenesis.

PTH/SDF-1α cotherapy promotes proliferation, migration and osteogenic differentiation of human periodontal ligament stem cells

OBJECTIVES

Stromal cell-derived factor-1α (SDF-1α) plays an important role in tissue regeneration in various tissues including the periodontium. A potential limitation for its use derives from its sensitivity to cleavage by dipeptidyl peptidase-IV (DPP-IV). Parathyroid hormone (PTH) reduces enzymatic activity of DPP-IV and is suggested to be a promising agent for periodontal tissue repair. The purpose of this study was to provide insight into how SDF-1α and intermittent PTH treatment might affect proliferation, migration and osteogenic differentiation of human periodontal ligament stem cells (PDLSCs) in vitro.

MATERIALS AND METHODS

PDLSCs were isolated by the limiting dilution method. Surface markers were quantified by flow cytometry. Cell-counting kit-8 (CCK8), cell migration assay, alkaline phosphatase (ALP) activity assay, alizarin red staining and RT-PCR were used to determine viability, migration and osteogenic differentiation of PDLSCs.

RESULTS

PDLSCs were positive for CD44, CD73, CD90, CD105, CD166 and STRO-1 and negative for CD14, CD34 and CD45. PTH/SDF-1α cotherapy significantly promoted cell proliferation, chemotactic capability, ALP activity and mineral deposition (P<.05). Gene expression level of bone sialoprotein (BSP), runt-related transcription factor 2 (Runx2) and osteocalcin (OCN) were all up-regulated (P<.05).

CONCLUSIONS

PTH/SDF-1α cotherapy promoted proliferation, migration and osteogenic differentiation of PDLSCs in vitro. Cotherapy seemed to have potential to promote periodontal tissue regeneration by facilitating chemotaxis of PDLSCs to the injured site, followed by promoting proliferation and osteogenic differentiation of these cells.

PTH/SDF-1α cotherapy induces CD90+CD34- stromal cells migration and promotes tissue regeneration in a rat periodontal defect model

Stromal cell-derived factor-1α (SDF-1α) is a key stem cell homing factor that is crucial for recruitment of stem cells to many diseased organs. However, the therapeutic activity of SDF-1α is potentially limited by N-terminal cleavage at position-2 proline by a cell surface protein CD26/dipeptidyl peptidase-IV (DPP-IV). Parathyroid hormone (PTH) is a DPP-IV inhibitor and has been suggested as a promising agent for periodontal tissue repair. The purpose of this study was to explore the effects of a cell-free system comprising SDF-1α and scaffold plus PTH systemic application on periodontal tissue regeneration in vivo. The results showed that PTH/SDF-1α cotherapy improved the quantity of regenerated bone and resulted in better organization of ligament interface. We further investigated the possible mechanisms, and found that PTH/SDF-1α cotherapy enhanced CD90+CD34- stromal cells migration in vivo, increased the number of CXCR4 + cells in periodontal defects, induced early bone osteoclastogenesis and enhanced the expression of runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP) and collagen I (Col I) in newly formed bone tissue. In conclusion, this cell-free tissue engineering system with local administration of SDF-1α and systemic application of PTH could be employed to induce CD90+CD34- stromal cells recruitment and promote periodontal tissue regeneration.