Transient inhibition of transforming growth factor-beta1 in human diabetic CD34+ cells enhances vascular reparative functions

The role of telomerase reverse transcriptase in the mitochondrial protective functions of Angiotensin-(1-7) in diabetic CD34+ cells

Angiotensin (Ang)-(1-7) stimulates vasoprotective functions of diabetic (DB) CD34+ hematopoietic stem/progenitor cells partly by decreasing reactive oxygen species (ROS), increasing nitric oxide (NO) levels and decreasing TGFβ1 secretion. Telomerase reverse transcriptase (TERT) translocates to mitochondria and regulates ROS generation. Alternative splicing of TERT results in variants α-, β- and α-β-TERT, which may oppose functions of full-length (FL) TERT. This study tested if the protective functions of Ang-(1-7) or TGFβ1-silencing are mediated by mitoTERT and that diabetes decreases FL-TERT expression by inducing splicing. CD34+ cells were isolated from the peripheral blood mononuclear cells of nondiabetic (ND, n = 68) or DB (n = 74) subjects. NO and mitoROS levels were evaluated by flow cytometry. TERT splice variants and mitoDNA-lesions were characterized by qPCR. TRAP assay was used for telomerase activity. Decoy peptide was used to block mitochondrial translocation (mitoXTERT). TERT inhibitor or mitoXTERT prevented the effects of Ang-(1-7) on NO or mitoROS levels in DB-CD34+ cells. FL-TERT expression and telomerase activity were lower and mitoDNA-lesions were higher in DB cells compared to ND and were reversed by Ang-(1-7) or TGFβ1-silencing. The prevalence of TERT splice variants, with predominant β-TERT expression, was higher and the expression of FL-TERT was lower in DB cells (n = 25) compared to ND (n = 30). Ang-(1-7) or TGFβ1-silencing decreased TERT-splicing and increased FL-TERT. Blocking of β-splicing increased FL-TERT and protected mitoDNA in DB-cells. The findings suggest that diabetes induces TERT-splicing in CD34+ cells and that β-TERT splice variant largely contributes to the mitoDNA oxidative damage.

Aldose Reductase as a Key Target in the Prevention and Treatment of Diabetic Retinopathy: A Comprehensive Review

The escalating global prevalence of diabetes mellitus (DM) over the past two decades has led to a persistent high incidence of diabetic retinopathy (DR), necessitating screening for early symptoms and proper treatment. Effective management of DR aims to decrease vision impairment by controlling modifiable risk factors including hypertension, obesity, and dyslipidemia. Moreover, systemic medications and plant-based therapy show promise in advancing DR treatment. One of the key mechanisms related to DR pathogenesis is the polyol pathway, through which aldose reductase (AR) catalyzes the conversion of glucose to sorbitol within various tissues, including the retina, lens, ciliary body and iris. Elevated glucose levels activate AR, leading to osmotic stress, advanced glycation end-product formation, and oxidative damage. This further implies chronic inflammation, vascular permeability, and angiogenesis. Our comprehensive narrative review describes the therapeutic potential of aldose reductase inhibitors in treating DR, where both synthetic and natural inhibitors have been studied in recent decades. Our synthesis aims to guide future research and clinical interventions in DR management.

Stem cells and diabetic retinopathy: From models to treatment

Diabetic retinopathy is a common yet complex microvascular disease, caused as a complication of diabetes mellitus. Associated with hyperglycemia and subsequent metabolic abnormalities, advanced stages of the disease lead to fibrosis, subsequent visual impairment and blindness. Though clinical postmortems, animal and cell models provide information about the progression and prognosis of diabetic retinopathy, its underlying pathophysiology still needs a better understanding. In addition to it, the loss of pericytes, immature retinal angiogenesis and neuronal apoptosis portray the disease treatment to be challenging. Indulged with cell loss of both vascular and neuronal type cells, novel therapies like cell replacement strategies by various types of stem cells have been sightseen as a possible treatment of the disease. This review provides insight into the pathophysiology of diabetic retinopathy, current models used in modelling the disease, as well as the varied aspects of stem cells in generating three-dimensional retinal models. Further outlook on stem cell therapy and the future directions of stem cell treatment in diabetic retinopathy have also been contemplated.

Unconventional avenues to decelerated diabetic retinopathy

Diabetic retinopathy (DR) is an important microvascular complication of diabetes mellitus (DM), causing significant visual impairment worldwide. Current gold standards for retarding the progress of DR include blood sugar control and regular fundus screening. Despite these measures, the incidence and prevalence of DR and vision-threatening DR remain high. Given its slowly progressive course and long latent period, opportunities to contain or slow DR before it threatens vision must be explored. This narrative review assesses the recently described unconventional strategies to retard DR progression. These include gut-ocular flow, gene therapy, mitochondrial dysfunction-oxidative stress, stem cell therapeutics, neurodegeneration, anti-inflammatory treatments, lifestyle modification, and usage of phytochemicals. These therapies impact DR directly, while some of them also influence DM control. Most of these strategies are currently in the preclinical stage, and clinical evidence remains low. Nevertheless, our review suggests that these approaches have the potential for human use to prevent the progression of DR.

Transforming growth factor-β1/Thrombospondin-1/CD47 axis mediates dysfunction in CD34+ cells derived from diabetic older adults

Aging with diabetes is associated with impaired vasoprotective functions and decreased nitric oxide (NO) generation in CD34+ cells. Transforming growth factor- β1 (TGF-β1) is known to regulate hematopoietic functions. This study tested the hypothesis that transforming growth factor- β1 (TGF-β1) is upregulated in diabetic CD34+ cells and impairs NO generation via thrombospondin-1 (TSP-1)/CD47/NO pathway. CD34+ cells from nondiabetic (ND) (n=58) or diabetic older adults (DB) (both type 1 and type 2) (n=62) were isolated from peripheral blood. TGF-β1 was silenced by using an antisense delivered as phosphorodiamidate morpholino oligomer (PMO-TGF-β1). Migration and proliferation in response to stromal-derived factor-1α (SDF-1α) were evaluated. NO generation and eNOS phosphorylation were determined by flow cytometry. CD34+ cells from older, but not younger, diabetics have higher expression of TGF-β1 compared to that observed in cells derived from healthy individuals (P<0.05, n=14). TSP-1 expression was higher (n=11) in DB compared to ND cells. TGFβ1-PMO decreased the secretion of TGF-β1, which was accompanied with decreased TSP-1 expression. Impaired proliferation, migration and NO generation in response to SDF-1α in DB cells were reversed by TGF-β1-PMO (n=6). TSP-1 inhibited migration and proliferation of nondiabetic CD34+ cells that was reversed by CD47-siRNA, which also restored these responses in diabetic CD34+ cells. TSP-1 opposed SDF-1α-induced eNOS phosphorylation at Ser1177 that was reversed by CD47-siRNA. These results infer that increased TGF-β1 expression in CD34+ cells induces dysfunction in CD34+ cells from diabetic older adults via TSP-1/CD47-dependent inhibition of NO generation.

Transforming growth factor-β1 signalling triggers vascular endothelial growth factor resistance and monocyte dysfunction in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) leads to monocyte dysfunction associated with atherogenesis and defective arteriogenesis. Transforming growth factor (TGF)-β1, placenta growth factor (PlGF)-1 and vascular endothelial growth factor (VEGF)A play important roles in atherogenesis and arteriogenesis. VEGF-receptor (VEGFR)-mediated monocyte migration is inhibited in T2DM (VEGFA resistance), while TGF-β1-induced monocyte migration is fully functional. Therefore, we hypothesize that TGF-β antagonises the VEGFA responses in human monocytes. We demonstrate that monocytes from T2DM patients have an increased migratory response towards low concentrations of TGF-β1, while PlGF-1/VEGFA responses are mitigated. Mechanistically, this is due to increased expression of type II TGF-β receptor in monocytes under high-glucose conditions and increased expression of soluble (s)VEGFR1, which is known to interfere with VEGFA signalling. VEGFA resistance in monocytes from T2DM patients can be rescued by either experimental down-regulation of TGF-β receptor expression in vitro or by functional blocking of TGF-β signalling using either a TGF-β receptor kinase inhibitor or a TGF-β neutralizing antibody. Our data demonstrate that both T2DM and high-glucose potentiate the TGF-β pathway. TGF-β signalling impairs VEGFR-mediated responses in T2DM monocytes and in this way contributes to mononuclear cell dysfunction, provide novel insights into T2DM vascular dysfunction.

Concise review: current trends on applications of stem cells in diabetic nephropathy

Diabetic nephropathy, with high prevalence, is the main cause of renal failure in diabetic patients. The strategies for treating DN are limited with not only high cost but an unsatisfied effect. Therefore, the effective treatment of DN needs to be explored urgently. In recent years, due to their self-renewal ability and multi-directional differentiation potential, stem cells have exerted therapeutic effects in many diseases, such as graft-versus-host disease, autoimmune diseases, pancreatic diseases, and even acute kidney injury. With the development of stem cell technology, stem cell-based regenerative medicine has been tried to be applied to the treatment of DN. Related stem cells include embryonic stem cells, induced pluripotent stem cells, mesenchymal cells, and endothelial progenitor cells. Undoubtedly, stem cell transplantation has achieved certain results in the treatment of DN animal models. However, stem cell therapy still remains certain thorny issues during treatment. For instance, poor engraftment and limited differentiation of stem cells caused by the diabetic microenvironment, differentiation into unwanted cell lineages, and malignant transformation or genetic aberrations of stem cells. At present, various researches on the therapeutic effects of stem cells in DN with different opinions are reported and the specific mechanism of stem cells is still unclear. We review here the potential mechanism of stem cells as new therapeutic agents in the treatment of DN. Also, we review recent findings and updated information about not only the utilization of stem cells on DN in both preclinical and clinical trials but limitations and future expectations of stem cell-based therapy for DN.

Characteristics of Neuropeptide-Containing Innervation, Tissue Remodeling, Growth, and Vascularity in Noses of Patients With Cleft Lip and Palate

OBJECTIVE

To detect the appearance and distribution of factors regulating remodeling, innervation, growth, and vascularity of the nasal tissue affected by cleft lip and palate (CLP).

DESIGN

Morphological analysis of human tissue.

SETTING

Cleft and craniofacial center.

PARTICIPANTS

Fifteen patients who underwent CLP rhinoplasty, 7 control patients.

INTERVENTIONS

Rhinoplasty.

MAIN OUTCOME MEASURES

Immunohistochemistry was performed with protein gene product (PGP) 9.5, transforming growth factor β1 (TGFβ1), vascular endothelial growth factor (VEGF), cluster of differentiation 34 (CD34), matrix metalloproteinase 2 (MMP2), MMP9, and tissue inhibitor of metalloproteinase 2 (TIMP2). The results were evaluated semiquantitatively. Spearman rank order correlation coefficient and Mann-Whitney U test were used for statistical analysis.

RESULTS

Cleft lip and palate-affected tissue revealed dense and loose connective tissue, adipose cells, and hyaline cartilage, along with numerous CD34-positive endotheliocytes and regions of VEGF-positive neoangiogenesis. We observed moderate to numerous PGP 9.5-positive nerve fibers. Transforming growth factor β1, MMP2, MMP9, and TIMP2 were found in cartilage and connective tissue. Cleft lip and palate-affected tissue compared to control samples showed a statistically significant difference in PGP 9.5 (P = .006), VEGF (P = .001), MMP2 (P = .002), MMP9 (P = .013), and TIMP2 (P < .001) expression. We observed a strong, positive correlation between VEGF and MMP9 (P = .027; r _S = 0.705).

CONCLUSIONS

The moderate expression of TGFβ1 and increased distribution of VEGF, MMP2, MMP9, and TIMP2 demonstrate an active extracellular matrix remodeling and angiogenesis, performed by proteases. The cartilaginous septum of the nose is an example of balance between tissue degradation and its suppression, demonstrated by the relationship between MMPs and TIMPs and the presence of VEGF.

Adult Stem Cell Therapeutics in Diabetic Retinopathy

Diabetic retinopathy (DR), a complication of diabetes, is one of the leading causes of blindness in working-age adults. The pathology of the disease prevents the endogenous stem cells from participating in the natural repair of the diseased retina. Current treatments, specifically stem cell therapeutics, have shown variable efficacy in preclinical models due to the multi-faceted nature of the disease. Among the various adult stem cells, mesenchymal stem cells, especially those derived from adipose tissue and bone marrow, have been explored as a possible treatment for DR. This review summarizes the current literature around the various adult stem cell treatments for the disease and outlines the benefits and limitations of the therapeutics that are being explored in the field. The paracrine nature of adipose stem cells, in particular, has been highlighted as a potential solution to the lack of a homing and conducive environment that poses a challenge to the implantation of exogenous stem cells in the target tissue. Various methods of mesenchymal stem cell priming to adapt to a hostile retinal microenvironment have been discussed. Current clinical trials and potential safety concerns have been examined, and the future directions of stem cell therapeutics in DR have also been contemplated.

The vasoreparative potential of endothelial colony-forming cells in the ischemic retina is enhanced by cibinetide, a non-hematopoietic erythropoietin mimetic

PURPOSE

Retinal ischemia remains a common sight threatening end-point in blinding diseases such as diabetic retinopathy and retinopathy of prematurity. Endothelial colony forming cells (ECFCs) represent a subpopulation of endothelial progenitors with therapeutic utility for promoting reparative angiogenesis in the ischaemic retina. The current study has investigated the potential of enhancing this cell therapy approach by the dampening of the pro-inflammatory milieu typical of ischemic retina. Based on recent findings that ARA290 (cibinetide), a peptide based on the Helix-B domain of erythropoietin (EPO), is anti-inflammatory and tissue-protective, the effect of this peptide on ECFC-mediated vascular regeneration was studied in the ischemic retina.

METHODS

The effects of ARA290 on pro-survival signaling and function were assessed in ECFC cultures in vitro. Efficacy of ECFC transplantation therapy to promote retinal vascular repair in the presence and absence of ARA290 was studied in the oxygen induced retinopathy (OIR) model of retinal ischemia. The inflammatory cytokine profile and microglial activation were studied as readouts of inflammation.

RESULTS

ARA290 activated pro-survival signaling and enhanced cell viability in response to H₂O₂-mediated oxidative stress in ECFCs in vitro. Preconditioning of ECFCs with EPO or ARA290 prior to delivery to the ischemic retina did not enhance vasoreparative function. ARA290 delivered systemically to OIR mice reduced pro-inflammatory expression of IL-1β and TNF-α in the mouse retina. Following intravitreal transplantation, ECFCs incorporated into the damaged retinal vasculature and significantly reduced avascular area. The vasoreparative function of ECFCs was enhanced in the presence of ARA290 but not EPO.

DISCUSSION

Regulation of the pro-inflammatory milieu of the ischemic retina can be enhanced by ARA290 and may be a useful adjunct to ECFC-based cell therapy for ischemic retinopathies.

Collagen biomaterial stimulates the production of extracellular vesicles containing microRNA-21 and enhances the proangiogenic function of CD34+ cells

CD34⁺ cells are promising for revascularization therapy, but their clinical use is limited by low cell counts, poor engraftment, and reduced function after transplantation. In this study, a collagen type I biomaterial was used to expand and enhance the function of human peripheral blood CD34⁺ cells, and potential underlying mechanisms were examined. Compared to the fibronectin control substrate, biomaterial-cultured CD34⁺ cells from healthy donors had enhanced proliferation, migration toward VEGF, angiogenic potential, and increased secretion of CD63⁺CD81⁺ extracellular vesicles (EVs). In the biomaterial-derived EVs, greater levels of the angiogenic microRNAs (miRs), miR-21 and -210, were detected. Notably, biomaterial-cultured CD34⁺ cells had reduced mRNA and protein levels of Sprouty (Spry)1, which is an miR-21 target and negative regulator of endothelial cell proliferation and angiogenesis. Similar to the results of healthy donor cells, biomaterial culture increased miR-21 and -210 expression in CD34⁺ cells from patients who underwent coronary artery bypass surgery, which also exhibited improved VEGF-mediated migration and angiogenic capacity. Therefore, collagen biomaterial culture may be useful for expanding the number and enhancing the function of CD34⁺ cells in patients, possibly mediated through suppression of Spry1 activity by EV-derived miR-21. These results may provide a strategy to enhance the therapeutic potency of CD34⁺ cells for vascular regeneration.-McNeill, B., Ostojic, A., Rayner, K. J., Ruel, M., Suuronen, E. J. Collagen biomaterial stimulates the production of extracellular vesicles containing microRNA-21 and enhances the proangiogenic function of CD34⁺ cells.

Hematopoietic stem/progenitor involvement in retinal microvascular repair during diabetes: Implications for bone marrow rejuvenation

The widespread nature of diabetes affects all organ systems of an individual including the bone marrow. Long-term damage to the cellular and extracellular components of the bone marrow leads to a rapid decline in the bone marrow-hematopoietic stem/progenitor cells (HS/PCs) compartment. This review will highlight the importance of bone marrow microenvironment in maintaining bone marrow HS/PC populations and the contribution of these key populations in microvascular repair during the natural history of diabetes. The autonomic nervous system can initiate and propagate bone marrow dysfunction in diabetes. Systemic pharmacological strategies designed to protect the bone marrow-HS/PC population from diabetes induced-oxidative stress and advanced glycation end product accumulation represent a new approach to target diabetic retinopathy progression. Protecting HS/PCs ensures their participation in vascular repair and reduces the risk of vasogdegeneration occurring in the retina.

Increase in acid sphingomyelinase level in human retinal endothelial cells and CD34+ circulating angiogenic cells isolated from diabetic individuals is associated with dysfunctional retinal vasculature and vascular repair process in diabetes

BACKGROUND

Diabetic retinopathy is a microvascular disease that results from retinal vascular degeneration and defective repair due to diabetes-induced endothelial progenitor dysfunction.

OBJECTIVE

Understanding key molecular factors involved in vascular degeneration and repair is paramount for developing effective diabetic retinopathy treatment strategies. We propose that diabetes-induced activation of acid sphingomyelinase (ASM) plays essential role in retinal endothelial and CD34+ circulating angiogenic cell (CAC) dysfunction in diabetes.

METHODS

Human retinal endothelial cells (HRECs) isolated from control and diabetic donor tissue and human CD34+ CACs from control and diabetic patients were used in this study. ASM messenger RNA and protein expression were assessed by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. To evaluate the effect of diabetes-induced ASM on HRECs and CD34+ CACs function, tube formation, CAC incorporation into endothelial tubes, and diurnal release of CD34+ CACs in diabetic individuals were determined.

RESULTS

ASM expression level was significantly increased in HRECs isolated from diabetic compared with control donor tissue, as well as CD34+ CACs and plasma of diabetic patients. A significant decrease in tube area was observed in HRECs from diabetic donors compared with control HRECs. The tube formation deficiency was associated with increased expression of ASM in diabetic HRECs. Moreover, diabetic CD34+ CACs with high ASM showed defective incorporation into endothelial tubes. Diurnal release of CD34+ CACs was disrupted with the rhythmicity lost in diabetic patients.

CONCLUSION

Collectively, these findings support that diabetes-induced ASM upregulation has a marked detrimental effect on both retinal endothelial cells and CACs.

Advances in bone marrow stem cell therapy for retinal dysfunction

The most common cause of untreatable vision loss is dysfunction of the retina. Conditions, such as age-related macular degeneration, diabetic retinopathy and glaucoma remain leading causes of untreatable blindness worldwide. Various stem cell approaches are being explored for treatment of retinal regeneration. The rationale for using bone marrow stem cells to treat retinal dysfunction is based on preclinical evidence showing that bone marrow stem cells can rescue degenerating and ischemic retina. These stem cells have primarily paracrine trophic effects although some cells can directly incorporate into damaged tissue. Since the paracrine trophic effects can have regenerative effects on multiple cells in the retina, the use of this cell therapy is not limited to a particular retinal condition. Autologous bone marrow-derived stem cells are being explored in early clinical trials as therapy for various retinal conditions. These bone marrow stem cells include mesenchymal stem cells, mononuclear cells and CD34+ cells. Autologous therapy requires no systemic immunosuppression or donor matching. Intravitreal delivery of CD34+ cells and mononuclear cells appears to be tolerated and is being explored since some of these cells can home into the damaged retina after intravitreal administration. The safety of intravitreal delivery of mesenchymal stem cells has not been well established. This review provides an update of the current evidence in support of the use of bone marrow stem cells as treatment for retinal dysfunction. The potential limitations and complications of using certain forms of bone marrow stem cells as therapy are discussed. Future directions of research include methods to optimize the therapeutic potential of these stem cells, non-cellular alternatives using extracellular vesicles, and in vivo high-resolution retinal imaging to detect cellular changes in the retina following cell therapy.

Stem cell therapies in the treatment of diabetic retinopathy and keratopathy

Nonproliferative diabetic retinopathy (DR) is characterized by multiple degenerative changes that could be potentially corrected by stem cell therapies. Most studies so far have attempted to alleviate typical abnormalities of early retinopathy, including vascular hyperpermeability, capillary closure and pericyte dropout. Success was reported with adult stem cells (vascular progenitors or adipose stem cells), as well as induced pluripotent stem cells from cord blood. The cells were able to associate with damaged vessels in both pericyte and endothelial lining positions in models of DR and ischemia-reperfusion. In some diabetic models, functional amelioration of vasculature and electroretinograms was noted. Another approach for endogenous progenitor cell therapy is to normalize dysfunctional diabetic bone marrow and residing endothelial progenitors using NO donors, PPAR-δ and -γ agonists, or inhibition of TGF-β. A potentially important strategy would be to reduce neuropathy by stem cell inoculations, either naïve (e.g., paracrine-acting adipose stem cells) or secreting specific neuroprotectants, such as ciliary neurotrophic factor or brain-derived neurotrophic factor that showed benefit in amyotrophic lateral sclerosis and Parkinson's disease. Recent advances in stem cell therapies for diabetic retinal microangiopathy may form the basis of first clinical trials in the near future. Additionally, stem cell therapies may prove beneficial for diabetic corneal disease (diabetic keratopathy) with pronounced epithelial stem cell dysfunction.

Growth factors/chemokines in diabetic vitreous and aqueous alter the function of bone marrow-derived progenitor (CD34⁺) cells in humans

Ocular ischemic microenvironment plays a critical role in the progression of diabetic retinopathy (DR). In this study, we investigated the effect of vitreous and aqueous obtained from proliferative DR patients on the function of CD34⁺ cells derived from healthy humans. Human CD34⁺ cells were incubated with vitreous or aqueous of subjects with PDR. After incubation, cell migration of CD34⁺ was evaluated with CXCL12. Intracellular levels of nitric oxide (NO) were measured with DAF-FM. Tube formation assay was used to evaluate the effect of treated CD34⁺ cells on in vitro angiogenesis. Angiogenic protein array and mass spectrometry (MS) were performed to ascertain the factors secreted by healthy nondiabetic CD34⁺ cells exposed to diabetic vitreous or aqueous. PDR vitreous/aqueous reduced migration of CD34⁺ cells (672.45 ± 42.1/736.75 ± 101.7 AFU; P < 0.01) and attenuated intracellular NO levels (182 ± 1.4/184.5 ± 6.3 AFU, P = 0.002). Pretreatment with PDR vitreous suppressed tube formation of human retinal endothelial cells (64 ± 1.6 vs. 80 ± 2.5). CD34⁺ exposed to PDR vitreous resulted in the increased expression of CXCL4 and serpin F1, whereas CD34⁺ exposed to PDR aqueous showed increased expression of CXCL4, serpin F1, and endothelin-1 (ET-1). MS analysis of CD34⁺ (exposed to PDR vitreous) expressed J56 gene segment, isoform 2 of SPARC-related modular calcium-binding protein 2, isoform 1 of uncharacterized protein c1 orf167, integrin α-M, and 40s ribosomal protein s21. Exposure of healthy nondiabetic CD34⁺ cells to PDR vitreous and aqueous resulted in decreased migration, reduced generation of NO, and altered paracrine secretory function. Our results suggest that the contribution of CD34⁺ cells to the aberrant neovascularization observed in PDR is driven more by the proangiogenic effects of the retinal cells rather than the influence of the vitreous.

Vasoreparative dysfunction of CD34+ cells in diabetic individuals involves hypoxic desensitization and impaired autocrine/paracrine mechanisms

We hypothesized that endothelial progenitor cells derived from individuals with diabetes would exhibit functional defects including inability to respond to hypoxia and altered paracrine/autocrine function that would impair the angiogenic potential of these cells. Circulating mononuclear cells isolated from diabetic (n = 69) and nondiabetic (n = 46) individuals were used to grow endothelial colony forming cells (ECFC), early endothelial progenitor cells (eEPCs) and isolate CD34⁺ cells. ECFCs and eEPCs were established from only 15% of the diabetic individuals tested thus directing our main effort toward examination of CD34⁺ cells. CD34⁺ cells were plated in basal medium to obtain cell-free conditioned medium (CM). In CM derived from CD34⁺ cells of diabetic individuals (diabetic-CM), the levels of stem cell factor, hepatocyte growth factor, and thrombopoietin were lower, and IL-1β and tumor necrosis factor (TNFα) levels were higher than CM derived from nondiabetic individuals (nondiabetic-CM). Hypoxia did not upregulate HIF1α in CD34⁺ cells of diabetic origin. Migration and proliferation of nondiabetic CD34⁺ cells toward diabetic-CM were lower compared to nondiabetic-CM. Attenuation of pressure-induced constriction, potentiation of bradykinin relaxation, and generation of cGMP and cAMP in arterioles were observed with nondiabetic-CM, but not with diabetic-CM. Diabetic-CM failed to induce endothelial tube formation from vascular tissue. These results suggest that diabetic subjects with microvascular complications exhibit severely limited capacity to generate ex-vivo expanded endothelial progenitor populations and that the vasoreparative dysfunction observed in diabetic CD34⁺ cells is due to impaired autocrine/paracrine function and reduced sensitivity to hypoxia.

Poly-ADP-ribose-polymerase inhibition ameliorates hind limb ischemia reperfusion injury in a murine model of type 2 diabetes

INTRODUCTION

Diabetes is known to increase poly-ADP-ribose-polymerase (PARP) activity and posttranslational poly-ADP-ribosylation of several regulatory proteins involved in inflammation and energy metabolism. These experiments test the hypothesis that PARP inhibition will modulate hind limb ischemia reperfusion (IR) in a mouse model of type-II diabetes and ameliorate the ribosylation and the activity/transnuclear localization of the key glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

METHODS

db/db mice underwent 1.5 hours of hind limb ischemia followed by 1, 7, or 24 hours of reperfusion. The treatment group received the PARP inhibitor PJ34 (PJ34) over a 24-hour period; the untreated group received Lactated Ringer (LR) at the same time points. IR muscles were analyzed for indices of PARP activity, fiber injury, metabolic activity, inflammation, GAPDH activity/intracellular localization, and poly-ADP-ribosylation of GAPDH.

RESULTS

PARP activity was significantly lower in the PJ34-treated groups than in the Lactated Ringer group at 7 and 24 hours of reperfusion. There was significantly less muscle fiber injury in the PJ34-treated group than in the Lactated Ringer-treated mice at 24 hours of reperfusion. PJ34 lowered levels of select proinflammatory molecules at 7 hours and 24 hours of IR. There were significant increases in metabolic activity only at 24 hours of IR in the PJ34 group, which temporally correlated with increase in GAPDH activity, decreased GAPDH poly-ADP-ribosylation, and nuclear translocation of GAPDH.

CONCLUSIONS

PJ34 reduced PARP activity, GAPDH ribosylation, and GAPDH translocation; ameliorated muscle fiber injury; and increased metabolic activity after hind limb IR injury in a murine model of type-II diabetes. PARP inhibition might be a therapeutic strategy after IR in diabetic humans.

Enhancing the function of CD34(+) cells by targeting plasminogen activator inhibitor-1

Previously, we showed that transient inhibition of TGF- β1 resulted in correction of key aspects of diabetes-induced CD34(+) cell dysfunction. In this report, we examine the effect of transient inhibition of plasminogen activator inhibitor-1 (PAI-1), a major gene target of TGF-β1 activation. Using gene array studies, we examined CD34(+) cells isolated from a cohort of longstanding diabetic individuals, free of microvascular complications despite suboptimal glycemic control, and found that the cells exhibited reduced transcripts of both TGF-β1 and PAI-1 compared to age, sex, and degree of glycemic control-matched diabetic individuals with microvascular complications. CD34(+) cells from diabetic subjects with microvascular complications consistently exhibited higher PAI-1 mRNA than age-matched non-diabetic controls. TGF- β1 phosphorodiamidate morpholino oligo (PMO) reduced PAI-1 mRNA in diabetic (p<0.01) and non-diabetic (p=0.05) CD34(+) cells. To reduce PAI-1 in human CD34(+) cells, we utilized PAI-1 siRNA, lentivirus expressing PAI-1 shRNA or PAI-1 PMO. We found that inhibition of PAI-1 promoted CD34(+) cell proliferation and migration in vitro, likely through increased PI3(K) activity and increased cGMP production. Using a retinal ischemia reperfusion injury model in mice, we observed that recruitment of diabetic CD34(+) cells to injured acellular retinal capillaries was greater after PAI-1-PMO treatment compared with control PMO-treated cells. Targeting PAI-1 offers a promising therapeutic strategy for restoring vascular reparative function in defective diabetic progenitors.

Rationale, design, and baseline characteristics of a trial for the prevention of diabetic atherosclerosis using a DPP-4 inhibitor: the Study of Preventive Effects of Alogliptin on Diabetic Atherosclerosis (SPEAD-A)

AIM

Alogliptin, an efficacious inhibitor of DPP-4 that improves glycemic control, as well as the pancreatic beta-cell function, is now increasingly used to accomplish glycemic targets in type 2 diabetic patients. Interestingly, recent experimental studies have shown that alogliptin exerts anti-atherosclerotic effects in GLP-1-dependent and -independent manners. The aim of the present ongoing study is to investigate the preventive effects of alogliptin on the progression of atherosclerosis in type 2 diabetic subjects using the carotid intima-media thickness (IMT), an established marker of cardiovascular disease.

METHODS AND RESULTS

The Study of Preventive Effects of Alogliptin on Diabetic Atherosclerosis (SPEAD-A) is a prospective, randomized, open-label, blinded-endpoint, multicenter, parallel-group, comparative study. Between March 2011 and March 2012, 341 participants were recruited at 11 clinical sites, and were randomly allocated either to an alogliptin treatment group (172 patients) or a conventional treatment group (169 patients). The primary outcomes are the changes in the maximum and mean IMT of the common carotid artery during a 24-month treatment period, as measured by carotid arterial echography. The secondary outcomes include the changes in glycemic control, parameters related to beta-cell function and diabetic nephropathy, the occurrence of cardiovascular events and adverse events and biochemical measurements reflecting vascular function.

CONCLUSIONS

This is the first study to address the effects of DPP-4 inhibitors on the progression of changes in the carotid IMT, with the patients without DPP-4 inhibitor treatment serving as a control group. The results will be available soon, and these findings are expected to provide clinical data that will be helpful in the prevention of diabetic atherosclerosis and subsequent cardiovascular disease.

Circulating mononuclear progenitor cells: differential roles for subpopulations in repair of retinal vascular injury

PURPOSE

We examined effect on retinal vascular homing of exogenous CD34(+) and CD14(+) progenitor cells using mouse models of chronic (streptozotocin [STZ]-induced diabetes) and acute (ischemia-reperfusion [I/R]) ocular vascular injury.

METHODS

STZ-treated mice of short or long duration (≤4, ≥11 months) diabetes, along with age- and sex-matched controls, were given intravitreous injections of human CD34(+) and CD14(+) cells isolated from healthy or diabetic donors alone or in combination. I/R injured mice were given diabetic or nondiabetic CD34(+) cells with mesenchymal stem cells (MSCs) or diabetic CD34(+) cells manipulated by ex vivo fucosylation with ASC-101. Injected cells were localized by fluorescent immunocytochemistry, and the degree of retinal vascular colocalization quantified morphometrically. Permeability was assessed by fluorescent albumin leakage.

RESULTS

Diabetic CD14(+) cells associated with vessels to a greater degree than diabetic CD34(+) cells. Vascular permeability was reduced only by nondiabetic cells and only at the highest number of cells tested. Diabetic CD34(+) cells consistently demonstrated reduced migration. There was a 2-fold or 4-fold increase over control in the specific localization of diabetic CD34(+) cells within the vasculature when these cells were co-administered with MSCs or ex vivo fucosylated prior to injection, respectively.

CONCLUSIONS

Diabetic CD14(+) cells, unlike diabetic CD34(+) cells, retain robust homing characteristics. CD34(+) or CD14(+) subsets rather than whole bone marrow or peripheral blood cells may prove more beneficial in autologous cell therapy for diabetics. Co-administration with MSCs or ex vivo fucosylation may enhance utility of CD34(+) cells in cell therapy for diabetic ocular conditions like macular ischemia and retinal nonperfusion.

Activation of the ACE2/angiotensin-(1-7)/Mas receptor axis enhances the reparative function of dysfunctional diabetic endothelial progenitors

We tested the hypothesis that activation of the protective arm of the renin angiotensin system, the angiotensin-converting enzyme 2 (ACE2)/angiotensin-(1-7) [Ang-(1-7)]/Mas receptor axis, corrects the vasoreparative dysfunction typically seen in the CD34(+) cells isolated from diabetic individuals. Peripheral blood CD34(+) cells from patients with diabetes were compared with those of nondiabetic controls. Ang-(1-7) restored impaired migration and nitric oxide bioavailability/cGMP in response to stromal cell-derived factor and resulted in a decrease in NADPH oxidase activity. The survival and proliferation of CD34(+) cells from diabetic individuals were enhanced by Ang-(1-7) in a Mas/phosphatidylinositol 3-kinase (PI3K)/Akt-dependent manner. ACE2 expression was lower, and ACE2 activators xanthenone and diminazine aceturate were less effective in inducing the migration in cells from patients with diabetes compared with controls. Ang-(1-7) overexpression by lentiviral gene modification restored both the in vitro vasoreparative functions of diabetic cells and the in vivo homing efficiency to areas of ischemia. A cohort of patients who remained free of microvascular complications despite having a history of longstanding inadequate glycemic control had higher expression of ACE2/Mas mRNA than patients with diabetes with microvascular complications matched for age, sex, and glycemic control. Thus, ACE2/Ang-(1-7)\Mas pathway activation corrects existing diabetes-induced CD34(+) cell dysfunction and also confers protection from development of this dysfunction.

Long-term type 1 diabetes influences haematopoietic stem cells by reducing vascular repair potential and increasing inflammatory monocyte generation in a murine model

AIMS/HYPOTHESIS

We sought to determine the impact of long-standing type 1 diabetes on haematopoietic stem/progenitor cell (HSC) number and function and to examine the impact of modulating glycoprotein (GP)130 receptor in these cells.

METHODS

Wild-type, gp130(-/-) and GFP chimeric mice were treated with streptozotocin to induce type 1 diabetes. Bone marrow (BM)-derived cells were used for colony-formation assay, quantification of side population (SP) cells, examination of gene expression, nitric oxide measurement and migration studies. Endothelial progenitor cells (EPCs), a population of vascular precursors derived from HSCs, were compared in diabetic and control mice. Cytokines were measured in BM supernatant fractions by ELISA and protein array. Flow cytometry was performed on enzymatically dissociated retina from gfp(+) chimeric mice and used to assess BM cell recruitment to the retina, kidney and blood.

RESULTS

BM cells from the 12-month-diabetic mice showed reduced colony-forming ability, depletion of SP-HSCs with a proportional increase in SP-HSCs residing in hypoxic regions of BM, decreased EPC numbers, and reduced eNos (also known as Nos3) but increased iNos (also known as Nos2) and oxidative stress-related genes. BM supernatant fraction showed increased cytokines, GP130 ligands and monocyte/macrophage stimulating factor. Retina, kidney and peripheral blood showed increased numbers of CD11b(+)/CD45(hi)/ CCR2(+)/Ly6C(hi) inflammatory monocytes. Diabetic gp130(-/-) mice were protected from development of diabetes-induced changes in their HSCs.

CONCLUSIONS/INTERPRETATION

The BM microenvironment of type 1 diabetic mice can lead to changes in haematopoiesis, with generation of more monocytes and fewer EPCs contributing to development of microvascular complications. Inhibition of GP130 activation may serve as a therapeutic strategy to improve the key aspects of this dysfunction.

Per2 mutation recapitulates the vascular phenotype of diabetes in the retina and bone marrow

In this study, we assessed whether Per2 clock gene-mutant mice exhibit a vascular phenotype similar to diabetes. Per2 (B6.129-Per2(tm1Drw)/J) or wild-type control mice 4 and 12 months of age were used. To evaluate diabetes-like phenotype in Per2 mutant mice, retina was quantified for mRNA expression, and degree of diabetic retinopathy was evaluated. Bone marrow neuropathy was studied by staining femurs for tyrosine hydroxylase (TH) and neurofilament 200 (NF-200). The rate of proliferation and quantification of bone marrow progenitor cells (BMPCs) was performed, and a threefold decrease in proliferation and 50% reduction in nitric oxide levels were observed in Per2 mutant mice. TH-positive nerve processes and NF-200 staining were reduced in Per2 mutant mice. Both retinal protein and mRNA expression of endothelial nitric oxide synthase were decreased by twofold. Other endothelial function genes (VEGFR2, VEGFR1) were downregulated (1.5-2-fold) in Per2 mutant retinas, whereas there was an upregulation of profibrotic pathway mediated by transforming growth factor-β1. Our studies suggest that Per2 mutant mice recapitulate key aspects of diabetes without the metabolic abnormalities, including retinal vascular damage, neuronal loss in the bone marrow, and diminished BMPC function.

Good news-bad news: the Yin and Yang of immune privilege in the eye

The eye and the brain are prototypical tissues manifesting immune privilege (IP) in which immune responses to foreign antigens, particularly alloantigens are suppressed, and even completely inhibited. Explanations for this phenomenon are numerous and mostly reflect our evolving understanding of the molecular and cellular processes underpinning immunological responses generally. IP is now viewed as a property of many tissues and the level of expression of IP varies not only with the tissue but with the nature of the foreign antigen and changes in the limited conditions under which privilege can operate as a mechanism of immunological tolerance. As a result, IP functions normally as a homeostatic mechanism preserving normal function in tissues, particularly those with highly specialized function and limited capacity for renewal such as the eye and brain. However, IP is relatively easily bypassed in the face of a sufficiently strong immunological response, and the privileged tissues may be at greater risk of collateral damage because its natural defenses are more easily breached than in a fully immunocompetent tissue which rapidly rejects foreign antigen and restores integrity. This two-edged sword cuts its swathe through the eye: under most circumstances, IP mechanisms such as blood-ocular barriers, intraocular immune modulators, induction of T regulatory cells, lack of lymphatics, and other properties maintain tissue integrity; however, when these are breached, various degrees of tissue damage occur from severe tissue destruction in retinal viral infections and other forms of uveoretinal inflammation, to less severe inflammatory responses in conditions such as macular degeneration. Conversely, ocular IP and tumor-related IP can combine to permit extensive tumor growth and increased risk of metastasis thus threatening the survival of the host.

Wound Healing Angiogenesis: Innovations and Challenges in Acute and Chronic Wound Healing

BACKGROUND

Formation of new blood vessels, by either angiogenesis or vasculogenesis, is critical for normal wound healing. Major processes in neovascularization include (i) growth-promoting or survival factors, (ii) proteolytic enzymes, (iii) activators of multiple differentiated and progenitor cell types, and (iv) permissible microenvironments. A central aim of wound healing research is to "convert" chronic, disease-impaired wounds into those that will heal.

THE PROBLEM

Reduced ability to re-establish a blood supply to the injury site can ultimately lead to wound chronicity.

BASIC/CLINICAL SCIENCE ADVANCES

(1) Human fetal endothelial progenitor cells can stimulate wound revascularization and repair following injury, as demonstrated in a novel mouse model of diabetic ischemic healing. (2) Advances in bioengineering reveal exciting alternatives by which wound repair may be facilitated via the creation of vascularized microfluidic networks within organ constructs created ex vivo for wound implantation. (3) A "personalized" approach to regenerative medicine may be enabled by the identification of protein components present within individual wound beds, both chronic and acute.

CLINICAL CARE RELEVANCE

Despite the development of numerous therapies, impaired angiogenesis and wound chronicity remain significant healthcare problems. As such, innovations in enhancing wound revascularization would lead to significant advances in wound healing therapeutics and patient care.

CONCLUSION

Insights into endothelial progenitor cell biology together with developments in the field of tissue engineering and molecular diagnostics should not only further advance our understanding of the molecular mechanisms regulating wound repair but also offer innovative solutions to promote the healing of chronic and acute wounds in vivo.

Cell-based therapies for diabetic retinopathy

Autologous endothelial progenitor cell (EPC) populations represent a novel treatment for therapeutic revascularization and vascular repair for diabetic patients with complications including diabetic retinopathy. Current therapies are applicable to late-stage disease and carry significant side effects, whereas cell-based therapy may provide an alternative by repairing areas of vasodegeneration and reversing ischemia. However, EPCs from diabetic patients with vascular complications are dysfunctional. Moreover, the diabetic environment poses its own challenges and complicates the use of autologous EPCs. Before EPCs become the ideal "cell therapy," the optimal EPC must be determined, any functional dysfunction must be corrected prior to use, and the diabetic milieu will require modification to accept the EPCs. This review describes the rationale for harnessing the vascular reparative properties of EPCs with emphasis on the molecular and phenotypic nature of healthy EPCs, how diabetes alters them, and novel strategies to improve dysfunctional EPCs.

Blockade of NADPH oxidase restores vasoreparative function in diabetic CD34+ cells

PURPOSE

The vasodegenerative phase of diabetic retinopathy is likely caused by endothelial dysfunction and reduced endothelial repair. Migration of endothelial progenitor cells (EPCs) into areas of vascular injury is critical to vascular repair. This key function, often defective in diabetes, is largely mediated by nitric oxide (NO), which is known to be inactivated by superoxide produced by NADPH oxidase. The authors tested the hypothesis that either increasing eNOS expression or inhibiting NADPH oxidase would restore the reparative function in diabetic EPCs.

METHODS

Peripheral blood was obtained from healthy (n = 27) and diabetic (n = 31) persons, and CD34(+) cells were isolated. Expression and activation of eNOS and NADPH oxidase and intracellular levels of NO, superoxide, and peroxynitrite were evaluated. cGMP production and migration to SDF-1α were also determined. Reparative function was evaluated in a mouse model of retinal ischemia-reperfusion injury.

RESULTS

Diabetic EPCs demonstrate reduced eNOS expression and decreased NO bioavailability and migration in response to SDF-1α. Increasing eNOS expression in diabetic cells by AVE3085 resulted in increased peroxynitrite levels and, therefore, did not enhance NO-mediated functions in vitro and in vivo. Expression of Nox2, NADPH oxidase activity, and superoxide levels were higher in diabetic than in nondiabetic EPCs. Pretreatment with apocynin or gp91ds-tat increased NO bioavailability without increasing eNOS activity in response to SDF-1α. Ex vivo NADPH oxidase inhibition in diabetic cells restored migratory function in vitro and enhanced their homing to ischemic retinal vasculature in vivo.

CONCLUSIONS

The NADPH oxidase system is a promising target for correcting vasoreparative dysfunction in diabetic EPCs.