Although previous reports have revealed the therapeutic potential of stem cell transplantation in diabetic polyneuropathy, the effects of cell transplantation on long-term diabetic polyneuropathy have not been investigated. In this study, we investigated whether the transplantation of dental pulp stem cells (DPSCs) ameliorated long-term diabetic polyneuropathy in streptozotocin (STZ)-induced diabetic rats. Forty-eight weeks after STZ injection, we transplanted DPSCs into the unilateral hindlimb skeletal muscles. Four weeks after DPSC transplantation (i.e., 52 weeks after STZ injection) the effects of DPSC transplantation on diabetic polyneuropathy were assessed. STZ-induced diabetic rats showed significant reductions in the sciatic motor/sensory nerve conduction velocity, increases in the current perception threshold, and decreases in capillary density in skeletal muscles and intra-epidermal nerve fiber density compared with normal rats, all of which were ameliorated by DPSC transplantation. Furthermore, sural nerve morphometrical analysis revealed that the transplantation of DPSCs significantly increased the myelin thickness and area. DPSC-conditioned media promoted the neurite outgrowth of dorsal root ganglion neurons and increased the viability and myelin-related protein expression of Schwann cells. These results indicated that the transplantation of DPSCs contributed to the neurophysiological and neuropathological recovery from a long duration of diabetic polyneuropathy.

Chemerin acts as a chemotactic factor for leukocyte populations expressing the G protein‐coupled receptor CMKLR1 (ChemR23). It is also an adipocytokine involved in obesity and metabolic syndromes. Previous studies have demonstrated that chemerin promotes angiogenesis in vitro, although the precise mechanism has not been elucidated. In this study, we have investigated whether chemerin regulates angiogenic processes and validated the associated mechanisms. In this study, chemerin stimulated angiogenesis in mice, which was demonstrated using Matrigel plug implantation assay, mouse corneal models of angiogenesis, and ex vivo rat aortic ring assay. To explore the mechanisms by which chemerin induced angiogenesis, we examined the effects of chemerin in human umbilical vein endothelium cells (HUVECs). Chemerin stimulated the differentiation of HUVECs into capillary‐like structures, promoted the proliferation of HUVECs, and functioned as a chemoattractant in migration assays. Chemerin induced the phosphorylation of Akt and p42/44 extracellular signal‐regulated kinase (ERK) in HUVECs and chemerin promotes angiogenesis via Akt and ERK. SiRNA against the chemerin receptor CMKLR1 but not that against another chemerin receptor, CCRL2, completely inhibited the chemerin‐induced migration and angiogenesis of HUVECs, which indicates that chemerin promotes the migration and angiogenic activities of HUVECs mainly through CMKLR1.

Introduction: Dental pulp stem cells (DPSCs) are mesenchymal stem cells located in dental pulp and are thought to be a potential source for cell therapy since DPSCs can be easily obtained from teeth extracted for orthodontic reasons. Obtained DPSCs can be cryopreserved until necessary and thawed and expanded when needed. The aim of this study is to evaluate the therapeutic potential of DPSC transplantation for diabetic polyneuropathy. Methods: DPSCs isolated from the dental pulp of extracted incisors of Sprague–Dawley rats were partly frozen in a −80 °C freezer for 6 months. Cultured DPSCs were transplanted into the unilateral hindlimb skeletal muscles 8 weeks after streptozotocine injection and the effects of DPSC transplantation were evaluated 4 weeks after the transplantation. Results: Transplantation of DPSCs significantly improved the impaired sciatic nerve blood flow, sciatic motor/sensory nerve conduction velocity, capillary number to muscle fiber ratio and intra-epidermal nerve fiber density in the transplanted side of diabetic rats. Cryopreservation of DPSCs did not impair their proliferative or differential ability. The transplantation of cryopreserved DPSCs ameliorated sciatic nerve blood flow and sciatic nerve conduction velocity as well as freshly isolated DPSCs. Conclusions: We demonstrated the effectiveness of DPSC transplantation for diabetic polyneuropathy even when using cryopreserved DPSCs, suggesting that the transplantation of DPSCs could be a promising tool for the treatment of diabetic neuropathy.

Diabetes is a major risk factor for atherosclerosis and ischemic vascular diseases. Recently, regenerative medicine is expected to be a novel therapy for ischemic diseases. Our previous studies have reported that transplantation of stem cells promoted therapeutic angiogenesis for diabetic neuropathy and ischemic vascular disease in a paracrine manner, but the precise mechanism is unclear. Therefore, we examined whether secreted factors from stem cells had direct beneficial effects on endothelial cells to promote angiogenesis. The soluble factors were collected as conditioned medium (CM) 48 h after culturing stem cells from human exfoliated deciduous teeth (SHED) in serum-free DMEM. SHED-CM significantly increased cell viability of human umbilical vein endothelial cells (HUVECs) in MTT assays and accelerated HUVECs migration in wound healing and Boyden chamber assays. In a Matrigel plug assay of mice, the migrated number of primary endothelial cells was markedly increased in the plug containing SHED-CM or SHED suspension. SHED-CM induced complex tubular structures of HUVECs in a tube formation assay. Furthermore, SHED-CM significantly increased neovascularization from the primary rat aorta, indicating that SHED-CM stimulated primary endothelial cells to promote comprehensive angiogenesis processes. The angiogenic effects of SHED-CM were the same or greater than the effective concentration of VEGF. In conclusion, SHED-CM directly stimulates vascular endothelial cells to promote angiogenesis and is promising for future clinical application.

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.

Dental pulp stem cells (DPSCs) are suitable for use in regenerative medicine. Cryopreserved human DPSCs (hDPSCs) ameliorate diabetic polyneuropathy, and the effects of hDPSC transplantation are related to VEGF and NGF secretion. This study evaluated the long-term effects of a single transplantation of hDPSCs on diabetic polyneuropathy. hDPSCs were obtained from human third molars extracted for orthodontic treatment, which were then transplanted into the unilateral hindlimb skeletal muscles 8 weeks after streptozotocin injection in nude mice. The effects of hDPSC transplantation were analyzed at 16 weeks post-transplantation. DPSC transplantation significantly improved delayed nerve conduction velocity, decreased blood flow, and increased sensory perception thresholds. Furthermore, the hDPSC-conditioned medium promoted the neurite outgrowth of dorsal root ganglion neurons. In conclusion, the therapeutic effects of hDPSC transplantation with a single injection last for prolonged periods and may be beneficial in treating long-term diabetic polyneuropathy.