Angioblast Derived from ES Cells Construct Blood Vessels and Ameliorate Diabetic Polyneuropathy in Mice

Kir6.2-deficient mice develop somatosensory dysfunction and axonal loss in the peripheral nerves

Glucose-responsive ATP-sensitive potassium channels (K_ATP) are expressed in a variety of tissues including nervous systems. The depolarization of the membrane potential induced by glucose may lead to hyperexcitability of neurons and induce excitotoxicity. However, the roles of K_ATP in the peripheral nervous system (PNS) are poorly understood. Here, we determine the roles of K_ATP in the PNS using K_ATP-deficient (Kir6.2-deficient) mice. We demonstrate that neurite outgrowth of dorsal root ganglion (DRG) neurons was reduced by channel closers sulfonylureas. However, a channel opener diazoxide elongated the neurite. K_ATP subunits were expressed in mouse DRG, and expression of certain subunits including Kir6.2 was increased in diabetic mice. In Kir6.2-deficient mice, the current perception threshold, thermal perception threshold, and sensory nerve conduction velocity were impaired. Electron microscopy revealed a reduction of unmyelinated and small myelinated fibers in the sural nerves. In conclusion, K_ATP may contribute to the development of peripheral neuropathy.

LncRNA SNHG15 relieves hyperglycemia-induced endothelial dysfunction via increased ubiquitination of thioredoxin-interacting protein

Numerous studies have revealed that hyperglycemia is a pivotal driver of diabetic vascular complications. However, the mechanisms of hyperglycemia-induced endothelial dysfunction in diabetes remain incompletely understood. This study aims to expound on the underlying mechanism of the endothelial dysfunction induced by hyperglycemia from the perspective of long non-coding RNAs (lncRNA). In this study, a downregulation of SNHG15 was observed in the ischemic hind limb of diabetic mice and high glucose (HG)-treated HUVECs. Functionally, the overexpression of SNHG15 promoted cell proliferation, migration, and tube formation, and suppressed cell apoptosis in HG-treated HUVECs. Mechanistically, SNHG15 reduced thioredoxin-interacting protein (TXNIP) expression by enhancing ITCH-mediated ubiquitination of TXNIP. TXNIP overexpression abrogated the protective effect of lncRNA SNHG15 overexpression on HG-induced endothelial dysfunction. The following experiment further confirmed that SNHG15 overexpression promoted angiogenesis of the ischemic hind limb in diabetic mice. In conclusion, SNHG15 is a novel protector for hyperglycemia-induced endothelial dysfunction via decreasing TXNIP expression.

LncRNA SNHG15 relieves hyperglycemia-induced endothelial dysfunction via increasing ubiquitination of thioredoxin-interacting protein

OBJECTIVE

Numerous evidence indicates that hyperglycemia is a pivotal driver of the vascular complications of diabetes. However, the mechanisms of hyperglycemia-induced endothelial dysfunction in diabetes remain incompletely understood. This study aims to expound on the underlying mechanism of the endothelial dysfunction induced by hyperglycemia from the perspective of long non-coding RNAs (lncRNA).

MATERIALS AND METHODS

Cell proliferation, migration, apoptosis, and tube formation were measured by cell counting kit-8 assay, transwell assay, flow cytometry, and tube formation assay, respectively. RNA pull-down and RNA-binding protein immunoprecipitation were used to detect the interaction between lncRNA SNHG15 and thioredoxin-interacting protein (TXNIP). Co-immunoprecipitation was used to detect the ubiquitination level of TXNIP and the interaction between TXNIP and E3 ubiquitin ligase ITCH.

RESULTS

A downregulation of SNHG15 was observed in the ischemic hind limb of diabetic mice and high glucose (HG)-treated HUVECs. Functionally, the overexpression of SNHG15 promoted cell proliferation, migration, and tube formation, and suppressed cell apoptosis in HG-treated HUVECs. Mechanically, SNHG15 reduced TXNIP expression by enhancing ITCH-mediated ubiquitination of TXNIP. TXNIP overexpression abrogated the protective effect of LncRNA SNHG15 overexpression on HG-induced endothelial dysfunction. The following experiment further confirmed that SNHG15 overexpression promoted angiogenesis of the ischemic hind limb in diabetic mice.

CONCLUSION

SNHG15 is a novel protector for hyperglycemia-induced endothelial dysfunction via decreasing TXNIP expression.

Direct Comparison of Therapeutic Effects on Diabetic Polyneuropathy between Transplantation of Dental Pulp Stem Cells and Administration of Dental Pulp Stem Cell-Secreted Factors

Stem cell transplantation is a potential novel therapy for diabetic polyneuropathy. Dental pulp stem cells (DPSCs) are attractive stem cell sources because DPSCs can be isolated from extracted teeth and cryopreserved while retaining viability. In this study, we directly compared the efficacy of the transplantation of DPSCs and the administration of the secreted factors from DPSCs (DPSC-SFs) on diabetic polyneuropathy. Eight weeks after streptozotocin injection, DPSCs (1.0 × 10⁶ cells/rat) or DPSC-SFs (1.0 mL/rat) were administered into the unilateral hindlimb skeletal muscles of diabetic Sprague-Dawley rats. DPSC transplantation and DPSC-SF administration did not affect blood glucose levels and body weights in the diabetic rats. Both DPSC transplantation and DPSC-SF administration significantly ameliorated sciatic nerve conduction velocity and sciatic nerve blood flow, accompanied by increases in muscle bundle size, vascular density in the skeletal muscles and intraepidermal nerve fiber density in the diabetic rats, while there was no difference between the results for DPSCs and DPSC-SFs. These results suggest that the efficacy of both DPSC transplantation and DPSC-SF administration for diabetic polyneuropathy four weeks after transplantation/administration was mainly due to the multiple secretomes secreted from transplanted DPSCs or directly injected DPSC-SFs in the early phase of transplantation/administration.

Secreted factors from cultured dental pulp stem cells promoted neurite outgrowth of dorsal root ganglion neurons and ameliorated neural functions in streptozotocin-induced diabetic mice

AIMS/INTRODUCTION

Transplantation of stem cells promotes axonal regeneration and angiogenesis in a paracrine manner. In the present study, we examined whether the secreted factors in conditioned medium of stem cells from human exfoliated deciduous teeth (SHED-CM) had beneficial effects on diabetic polyneuropathy in mice.

MATERIALS AND METHODS

Conditioned medium of stem cells from human exfoliated deciduous teeth was collected 48 h after culturing in serum-free Dulbecco's modified Eagle's medium (DMEM), and separated into four fractions according to molecular weight. Dorsal root ganglion neurons from C57BL/6J mice were cultured with SHED-CM or DMEM to evaluate the effect on neurite outgrowth. Streptozotocin-induced diabetic mice were injected with 100 μL of SHED-CM or DMEM into the unilateral hindlimb muscles twice a week over a period of 4 weeks. Peripheral nerve functions were evaluated by the plantar test, and motor and sensory nerve conduction velocities. Intraepidermal nerve fiber densities, capillary number-to-muscle fiber ratio, capillary blood flow and morphometry of sural nerves were also evaluated.

RESULTS

Conditioned medium of stem cells from human exfoliated deciduous teeth significantly promoted neurite outgrowth of dorsal root ganglion neurons compared with DMEM. Among four fractions of SHED-CM, the only fraction of <6 kDa promoted the neurite outgrowth of dorsal root ganglion neurons. In addition, SHED-CM significantly prevented decline in sensory nerve conduction velocities compared with DMEM in diabetic mice. Although SHED-CM did not improve intraepidermal nerve fiber densities or morphometry of sural nerves, SHED-CM ameliorated the capillary number-to-muscle fiber ratio and capillary blood flow.

CONCLUSIONS

These results suggested that SHED-CM might have a therapeutic effect on diabetic polyneuropathy through promoting neurite outgrowth, and the increase in capillaries might contribute to the improvement of neural function.

Conditioned media from dental pulp stem cells improved diabetic polyneuropathy through anti-inflammatory, neuroprotective and angiogenic actions: Cell-free regenerative medicine for diabetic polyneuropathy

AIMS/INTRODUCTION

Dental pulp stem cells (DPSCs) can be easily obtained from teeth for general orthodontic reasons. We have previously reported the therapeutic effects of DPSC transplantation for diabetic polyneuropathy. As abundant secretomes from DPSCs are considered to play a central role in the improvement of diabetic polyneuropathy, we investigated whether direct injection of DPSC-conditioned media (DPSC-CM) into hindlimb skeletal muscles ameliorates diabetic polyneuropathy in diabetic rats.

MATERIALS AND METHODS

DPSCs were isolated from the dental pulp of Sprague-Dawley rats. Eight weeks after the induction of diabetes, DPSC-CM was injected into the unilateral hindlimb skeletal muscles in both normal and diabetic rats. The effects of DPSC-CM on diabetic polyneuropathy were assessed 4 weeks after DPSC-CM injection. To confirm the angiogenic effect of DPSC-CM, the effect of DPSC-CM on cultured human umbilical vascular endothelial cell proliferation was investigated.

RESULTS

The administration of DPSC-CM into the hindlimb skeletal muscles significantly ameliorated sciatic motor/sensory nerve conduction velocity, sciatic nerve blood flow and intraepidermal nerve fiber density in the footpads of diabetic rats. We also showed that DPSC-CM injection significantly increased the capillary density of the skeletal muscles, and suppressed pro-inflammatory reactions in the sciatic nerves of diabetic rats. Furthermore, an in vitro study showed that DPSC-CM significantly increased the proliferation of umbilical vascular endothelial cells.

CONCLUSIONS

We showed that DPSC-CM injection into hindlimb skeletal muscles has a therapeutic effect on diabetic polyneuropathy through neuroprotective, angiogenic and anti-inflammatory actions. DPSC-CM could be a novel cell-free regenerative medicine treatment for diabetic polyneuropathy.

Schwann Cells as Crucial Players in Diabetic Neuropathy

Schwann cells maintain peripheral nerve structure and function by ensheathment of unmyelinated axons, myelination of myelinated axons, and secretion of neurotrophic factors, and these cells also play a crucial role in the pathogenic mechanisms of diabetic neuropathy. A decrease in unmyelinated and small myelinated axons appeared earlier than a decrease in large myelinated fibers in diabetic neuropathy. Electron microscopic studies of human diabetic neuropathy demonstrated edematous cell cytoplasm, aggregates of glycogen particles, and hyperplasia of the surrounding basal lamina in Schwann cells. Diabetic conditions also induces metabolic disorders, such as polyol pathway hyperactivity, activation of protein kinase C, and increased advanced glycosylation end products in Schwann cells, followed by the depletion of neurotrophic factor production.Cell transplantation using progenitor or stem cells is expected to cure diabetic neuropathy. Many studies demonstrated that the paracrine effect of abundant secreted factors from transplanted stem cells was crucial for the success of cell transplantation in diabetic neuropathy. Transplantation of progenitor or stem cells in diabetic animal models ameliorated impaired nerve conduction velocity, nerve blood flow, sensory disorders, and intraepidermal nerve fiber density, with an increase of myelin thickness. The supernatant from cultured dental pulp stem cells increased the proliferation and production of myelin-related protein in Schwann cells, suggesting that Schwann cells is the main target of cell transplantation for diabetic neuropathy.

Integrated approaches to spatiotemporally directing angiogenesis in host and engineered tissues

The field of tissue engineering has turned towards biomimicry to solve the problem of tissue oxygenation and nutrient/waste exchange through the development of vasculature. Induction of angiogenesis and subsequent development of a vascular bed in engineered tissues is actively being pursued through combinations of physical and chemical cues, notably through the presentation of topographies and growth factors. Presenting angiogenic signals in a spatiotemporal fashion is beginning to generate improved vascular networks, which will allow for the creation of large and dense engineered tissues. This review provides a brief background on the cells, mechanisms, and molecules driving vascular development (including angiogenesis), followed by how biomaterials and growth factors can be used to direct vessel formation and maturation. Techniques to accomplish spatiotemporal control of vascularization include incorporation or encapsulation of growth factors, topographical engineering, and 3D bioprinting. The vascularization of engineered tissues and their application in angiogenic therapy in vivo is reviewed herein with an emphasis on the most densely vascularized tissue of the human body - the heart.

STATEMENT OF SIGNIFICANCE

Vascularization is vital to wound healing and tissue regeneration, and development of hierarchical networks enables efficient nutrient transfer. In tissue engineering, vascularization is necessary to support physiologically dense engineered tissues, and thus the field seeks to induce vascular formation using biomaterials and chemical signals to provide appropriate, pro-angiogenic signals for cells. This review critically examines the materials and techniques used to generate scaffolds with spatiotemporal cues to direct vascularization in engineered and host tissues in vitro and in vivo. Assessment of the field's progress is intended to inspire vascular applications across all forms of tissue engineering with a specific focus on highlighting the nuances of cardiac tissue engineering for the greater regenerative medicine community.

Is Regenerative Medicine Ready for Prime Time in Diabetic Polyneuropathy?

PURPOSE OF REVIEW

After a prolonged warm-up period of basic research, several modalities of cell replacement therapies are under development for diseases with no available cure. Diabetic polyneuropathy (DPN) is one of the most prevalent chronic diabetes complications that causes sensorimotor dysfunction, subsequent high risks for lower limb amputations, and high mortality. Currently, no disease modifying therapy exists for DPN.

RECENT FINDINGS

Several types of well-documented stem/progenitor cells have been utilized for cell transplantation therapies in DPN model rodents: mesenchymal stromal cells (MSCs), endothelial progenitor cells (EPCs), and cells with similar characteristics of MSCs or EPCs derived from embryonic stem cells or induced pluripotent stem cells. Some recent experimental studies reported that these immature cells may have beneficial effects on DPN. Although the role of nerve regeneration in the pathology of DPN has not been sufficiently elucidated, many intervention studies attempting regenerative therapy of DPN have been reported. Further studies are needed to better evaluate the potential of regeneration in reversing the pathology of DPN.

Is Stem Cell Transplantation Ready for Prime Time in Diabetic Polyneuropathy?

Diabetic polyneuropathy (DPN) is the most common complication that emerges early in patients who have diabetes. Curative treatment for overt or symptomatic DPN has not been established, requiring much effort to explore new modalities. Thus, the use of various kinds of stem cells as a potential therapeutic option for DPN is of particular interest. The beneficial effects were proposed to be attributed to either cytokine released from transplanted stem cells or the differentiation of stem cells to substitute the damaged peripheral nerve. Furthermore, based on the concept that humoral factors secreted from stem cells play a pivotal role in tissue regeneration, the utilization of conditioned medium derived from the stem cell culture serves as a novel tool for regenerative therapy. However, many questions have not been yet answered to determine whether stem cell therapy is essential in clinical application of DPN. In this report, we review the current status of preclinical studies on stem cell therapy for DPN and discuss future prospects.

Transplantation of dental pulp stem cells suppressed inflammation in sciatic nerves by promoting macrophage polarization towards anti-inflammation phenotypes and ameliorated diabetic polyneuropathy

Aims/Introduction

Dental pulp stem cells (DPSCs) are thought to be an attractive candidate for cell therapy. We recently reported that the transplantation of DPSCs increased nerve conduction velocity and nerve blood flow in diabetic rats. In the present study, we investigated the immunomodulatory effects of DPSC transplantation on diabetic peripheral nerves.

Materials and Methods

DPSCs were isolated from the dental pulp of Sprague–Dawley rats and expanded in culture. Eight weeks after the streptozotocin injection, DPSCs were transplanted into the unilateral hindlimb skeletal muscles. Four weeks after DPSC transplantation, neurophysiological measurements, inflammatory gene expressions and the number of CD68‐positive cells in sciatic nerves were assessed. To confirm the immunomodulatory effects of DPSCs, the effects of DPSC‐conditioned media on lipopolysaccharide‐stimulated murine macrophage RAW264.7 cells were investigated.

Results

Diabetic rats showed significant delays in sciatic nerve conduction velocities and decreased sciatic nerve blood flow, all of which were ameliorated by DPSC transplantation. The number of CD68‐positive monocytes/macrophages and the gene expressions of M1 macrophage‐expressed cytokines, tumor necrosis factor‐α and interleukin‐1β, were increased in the sciatic nerves of the diabetic rats. DPSC transplantation significantly decreased monocytes/macrophages and tumor necrosis factor‐α messenger ribonucleic acid expression, and increased the gene expression of the M2 macrophage marker, CD206, in the sciatic nerves of the diabetic rats. The in vitro study showed that DPSC‐conditioned media significantly increased the gene expressions of interleukin‐10 and CD206 in lipopolysaccharide‐stimulated RAW264.7 cells.

Conclusions

These results suggest that DPSC transplantation promoted macrophages polarization towards anti‐inflammatory M2 phenotypes, which might be one of the therapeutic mechanisms for diabetic polyneuropathy.