Potential of dental pulp stem cells and their products in promoting peripheral nerve regeneration and their future applications

Table 1 Progress in application of dental pulp stem cells in treating models of peripheral nerve injury

Publication year	Cell source	Induction program	Pretransplantation procedure	Material(s)	Dose/concentration	Disease model	Experiment duration	Treatment effect	Ref.
2022	Human	DMEM + 10% (FBS + P/S)	3D culture	Fibrinogen, calcium chloride, and thrombin-like protein	3 × 105 cells	Avulsion of spinal motor roots in rats	12 wk	The transcription of TNF-α, IL-1β, IL-6, and IL-17 and the expression of anti-inflammatory cytokines (TGF-β, IL-4, IL-10, and IL-13) were increased; the animals in the reimplantation + 2D group showed the best functional recovery	[82]
2021	Human	α-MEM + 20% (FBS + P/S)	Collected and resuspended in GelMA-bFGF	10% GFD in a CSM tube	1 × 106 cells/mL	15 mm defect of the sciatic nerve in rats	12 wk	Cell based therapy repaired large gap defects in peripheral nerves; the differentiation of DPSCs into nerve cells and Schwann-like nerve cells and the formation of myelinated nerve fibers were observed	[98]
2021	Human	DMEM + 10% (FBS + P/S + NEAA)	NLCs differentiated from DPSCs	-	1 × 105 NLCs	10 mm sciatic nerve defect in athymic nude rats	12 wk	Two weeks after transplantation, approximately 75% of the transplanted cells differentiated into platelet-derived growth factor receptor alpha + OPCs expressing p75NTRd; transplantation promoted axon growth and improved nerve function	[145]
2021	Human	α-MEM + 15% FBS	Exosome collection	-	200 μg/100 μL	Mouse model of spinal cord injury	4 wk	Inhibited the ROS-MAPK-NFκB P65 signaling pathway to reduce M1 macrophage polarization, suppress the inflammatory response, and alleviate neurological damage	[121]
2020	Human	DMEM + 20% (FBS + P/S)	Preparation of scaffold-free cell sheets by coculture with FGF2	-	2 × 106 cells/cell sheet	Rat model of facial nerve crush injury	3 wk	Cell sheets promoted axonal regeneration and functional recovery through continuous delivery of neurotrophic factors such as BDNF and GDNF	[116]
2020	Human	α-MEM + 10% (FBS + P/S + NEAA)	Induction of DPSCs differentiation into N-DPSCs; induction of DPSCs differentiation into N-DPSCs	-	-	Rat model of sciatic nerve crush injury	1 mo	Both DPSCs and N-DPSCs promoted peripheral nerve repair through the expression of neurotrophic factors such as NGF, BDNF, and GDNF; the nerve repair effect of N-DPSCs was longer lasting	[146]
2019	Human (children)	DMEM + 15% (FBS+P/S)	-	-	5 × 105 cells in 4 μL DMEM	Unilateral facial nerve crush injury in rats	6 wk	Immature DPSCs promoted nerve regeneration and the formation of new myelin; the expression of nerve growth factor and anti-inflammatory cytokines (IL-6 and IL-10) increased significantly 7 d after treatment, and there was a decrease in the levels of soluble proinflammatory factors such as IL-2, IL-4, TNF-α, and IFN-γ	[87]
2019	Human	-	Induction of DPSCs differentiation into nerve cells	A PDO-based cell carrier	7.5 × 105 cells	6 mm defect of the sciatic nerve in rats	12 wk	Multiperforated PDO tubes were effective biomaterial carriers; delivery of DPSCs impacted the inflammatory environment and promoted nerve regeneration and functional recovery	[89]
2018	Human	-	Isolation of STRO-1+/c-Kit+/CD34+ cells	Collagen scaffolds	5 × 105 cells/animal	6 mm defect of the sciatic nerve in rats	4 wk	Nerve fiber regeneration and myelination and many myelinated axons were observed; DPSCs grafted into the sciatic nerve defect expressed the typical Schwann cell marker S100B and were positive for human NeuN	[12]
2018	Human	ADMEM + 10% FBS	Differentiated into neuronal cells (DF-DPSCs)	A conduit made from a Lyoplant membrane	-	7-8 mm defect of the sciatic nerve in rats	12 wk	DPSCs relieved neuropathic pain and inhibited inflammation in rats earlier than DF-DPSCs; at 12 wk after the operation, the expression of pAMPK/SIRT1 in DF-DPSCs and DPSCs increased, the expression of proinflammatory cytokines decreased, and the expression of NFκB decreased	[81]
2018	Human	ADMEM + 10% (FBS + P/S)	Differentiation into cholinergic neurons by adding D609	Biodegradable tubule and fibrin glue	1 × 106 DF-chNs	5 mm defect of the sciatic nerve in rats	8 wk	Transplanted DF-chNs promoted motor nerve regeneration and axon growth and expressed nerve growth factor receptor (p75NGFR)	[61]
2018	Human	-	-	An absorbable hemostat filled with human DPCs containing 1% atelocollagen, fibronectin, and laminin	3 × 105 cells	Crush injury of the sciatic nerve in rats	2 wk	DPCs stimulated Schwann cell differentiation and promoted peripheral nerve regeneration	[114]
2017	Human	Standard: α-MEM + 10% (FBS + NEAA + P/S). Differentiation: Standard + forskolin + bFGF + PDGF-AA + HRG1-β	Differentiation into Schwann-like cells (d-hDPSCs)	NeuraWrap™ conduits	-	15 mm defect of the sciatic nerve in rats	8 wk	Growth of axons, myelinated nerve fibers, and blood vessels; DPSCs still exerted strong angiogenic effects after differentiating into Schwann-like cells	[102]
2017	Human	α-MEM + 15% (FBS + AA + P/S + NEAA)	-	Fibrin conduits	2 × 106/20 μL	10 mm defect of the sciatic nerve in rats	2 wk	Promoted nerve and axon regeneration; the transplanted cells expressed BDNF near the cell body, and the expression level of caspase-3 decreased	[45]
2017	Human	ADMEM + 10% FBS	Induction of DPSCs differentiation into nerve cells	Fibrin glue scaffold and collagen tubulation	1 × 106 cells	5 mm defect of the sciatic nerve in rats	12 wk	Both hDPSCs and DF-hDPSCs promoted nerve regeneration and functional recovery; they could directly differentiate into nerve cells or facilitate nerve cell differentiation	[99]
2015	Human	α-MEM + 10% (FBS + P/S/AmB)	Transfection with Olig2 gene via a tetracycline (Tet) inducible system	-	2 × 105 cells	Mouse model of local sciatic nerve demyelination	6 wk	Recovery of sciatic nerve function; DPSCs differentiated into oligodendrocyte progenitors, and specific markers of oligodendrocyte progenitors and oligodendrocytes were expressed	[108]
2015	Human	DMEM + 10% FBS	G-CSF-induced stem cell mobilization (mobilized DPSCs and MDPSCs)	Collagen conduits	3.0 × 105 MDPSCs	5 mm defect of the sciatic nerve in rats	5 wk	MDPSCs secreted neurogenic/angiogenic factors and promoted peripheral nerve regeneration	[112]
2015	Human	Culture dishes containing essential medium (alpha modification) + 10% (FBS + P/S + amphotericin B)	Induction of DPSCs differentiation into OPCs by transfection with a plasmid containing the human Olig2 gene		2 × 105 cells	Sciatic nerve demyelination in mice	6 wk	DPSCs differentiated into OPCs, and transplantation promoted myelin sheath formation and peripheral nerve function recovery	[107]
2015	Human	DMEM + b-ME; DMEM + 10% (FBS + RA); DMEM + 10% (FBS + FSK + b-FGF + PDGF + HRG)	Differentiation of hDPSCs into Schwann-like cells	Cells combined with a pulsed electromagnetic field (PEMF)	1 × 106 cells/10 mL/rat	Crush injury of the peripheral nerve in rats	3 wk	Schwann-like cells derived from DPSCs exhibited the characteristics of glial cells, expressing CD104, S100, GFAP, laminin, and p75NTR; application of a PEMF promoted peripheral nerve regeneration after cell transplantation	[147]
2012	Human	DMEM + 10% FBS	-	-	1 × 106 cells	Rat spinal cord transection model	8 wk	DPSCs promoted axonal growth, differentiated into oligodendrocytes to treat spinal cord injury, and protected the nerve by inhibiting apoptosis and paracrine signaling	[105]
2018	Human	α-MEM + 10% (FBS + NEAA + P/S)	Application of fresh medium containing vitamin C cells reached approximately 80% confluence	-	-	Patients diagnosed with a traumatized permanent incisor	12 mo	HDPSCs transplantation promoted the regeneration of pulp tissue including neuronal tissue, and the neuron marker NeuN was expressed	[75]
	Human	PBS + P/S	Collection of hDPSCs aggregates	The root canals of human teeth	-	Immunocompromised mice	8 wk	Dental pulp tissue containing sensory nerves and blood vessels regenerated after HDPSCs transplantation
	Human	α-MEM + 10% (FBS + NEAA + P/S)	-	-	3 × 105 cells	Rats injected into the dorsal root ganglion	2 mo	HDPSCs exhibited the morphology of neurons and expressed TRPV1 and TRPM8
	Pig	PBS + P/S	Collection of hDPSCs aggregates	-	-	Permanent incisors of young female minipigs	3 mo	Pig DPSCs resulted in the 3D regeneration of dental pulp with neural function
2015	Pig	Culture medium + 10% (FBS + L-AA -2-P + P/S)	-	Fibrin membrane	-	Porcine intercostal nerve transection model	6 mo	DPSCs alleviated nerve injury and express NSE; neuroelectrophysiological evaluation showed that neurological function was restored	[88]
2020	Rat	α-MEM + 20% FBS	-	-	1 × 106 cells/rat	Diabetic rats	4 wk	Multiple factors secreted by DPSCs increased the nerve conduction velocity and blood flow to nerves	[118]
2019	Rat	α-MEM + glucose + 20% FBS	Collection of DPSCs-CM	-	1 mL/rat	Diabetic rats	4 wk	DPSCs-CM ameliorated peripheral neuropathy by exerting neuroprotective, angiogenic, and anti-inflammatory effects	[132]
2017	Rat	α-MEM + 20% FBS	-	-	1 × 106 cells	Streptozotocin-induced diabetes rat model	4 wk	Sensory disturbance was alleviated, the thickness and area of the myelin sheath increased, the transplanted DPSCs secreted multiple factors such as angiogenic factors, neurotrophic factors, and immunosuppressive factors	[84]
2015	Rat	α-MEM + glucose + 20% FBS	-	-	1 × 106 cells	Diabetic rats	4 wk	DPSCs transplantation relieved diabetic polyneuropathy by inhibiting inflammation, exerting immunomodulatory effects, and secreting neurotrophic factors	[86]
2015	Rat	α-MEM + 20% FBS	-	-	1 × 106 cells/limb	Diabetic rats	8 wk	DPSCs increased the nerve conduction velocity and blood flow to nerves and promoted an increase in the number of nerve fibers in diabetic rats	[83]
2013	Rat	DMEM + 10% (FBS + P/S)	-	-	1.5 × 105 cells	Crush injury of the optic nerve in rats	3 wk	Transplantation of DPSCs significantly increased the survival rate of retinal ganglion cells in rats and promote axonal regeneration	[58]
2007	Rat	-	Embedded in 10 mL type I collagen gel	10-mm silicone tube	1 × 105 cells	7 mm defect of the facial nerve in rats	2 wk	Regeneration of axons, blood vessels, and Schwann cells; Tuj1-positive axons and S100-positive Schwann-like supportive cells were found in regenerated nerves	[91]
2018	Rabbit	DMEM + 10% FBS	Construction of an acellular nerve graft for nerve regeneration	Xenogenic acellular nerve matrix	6 × 105 cells per graft	10 mm defect of the sciatic nerve in rabbits	3 mo	Regeneration of nerve space showed that acellular nerve grafts containing DPSCs treated with myroilysin had a strong neural induction effect	[148]

AA: Ascorbic acid; AmB: Amphotericin B; ADMEM: Advanced Dulbecco’s modified Eagle medium; bFGF: Basic fibroblast growth factor; b-ME: Beta-mercaptoethanol; BG: Beta-glycerophosphate; Dex: Dexamethasone; CSM: Cellulose/soy protein isolate composite membrane; DPSCs-CM: DPSCs-conditioned medium; DMEM: Dulbecco’s modified Eagle medium; DF-chNs: Differentiated cholinergic neurons; DF-DPSCs: Neuronal cells differentiated from DPSCs; FSK: Forskolin; bD609: Tricyclodecane-9-yl-xanthogenate; FBS: Fetal bovine serum; G-CSF: Granulocyte-colony stimulating factor; GFD: 10% GelMA hydrogel, recombinant human basic fibroblast growth factor and DPSCs; HRG1-β: Heregulin-β-1; L-AA-2-P: L-ascorbic acid-2-phosphate; NGF: Nerve growth factor; N-DPSCs: Neural-induced DPSCs; NSE: Neuron-specific enolase; NEAA: Nonessential amino acids; NLCs: Neural lineage cells; OPCs: Oligodendrocyte progenitor cells; P/S: Penicillin and streptomycin; PDGF-AA: Platelet-derived growth factor AA; PBS: Phosphate-buffered saline; PDGF: Platelet-derived growth factor; RA: All-trans retinoic acid; TGNCs: Trigeminal ganglion neuronal cells; IL: Interleukin; TNF: Tumor necrosis factor; TGF: Transforming growth factor.

Table 2 Research illustrating the ability of dental pulp stem cells to promote nerve regeneration in vitro

Publication year	Cell source	Induction protocol	Material(s) applied	Dose/concentration	Neurocyte type	Culture duration	Results	Ref.
2022	Human	DMEM + 20% (FBS + P/S + AA + bFGF)	Dental pulp cell sheets	3200 cells/cm2	SH-SY5Y neuroblastoma cells	3 d	Dental pulp cell sheets provided neurotrophic support by expressing NTF; the amount of neurotrophic factors produced by dental pulp cell sheets was sufficient to induce nerve regeneration in vitro and promote nerve repair in vivo; dental pulp cell sheets improved axon guidance and reduced axon branching	[113]
2020	Rat	α-MEM + 10% (FBS + P/S + NEAA)	DPSCs-CM	-	TGNCs from rats	3 wk	DPSCs-CM was found to contain significant levels of nerve growth factor, brain-derived neurotrophic factor, neurotrophic factor-3, and glial cell line-derived neurotrophic factor; DPSCs-CM increased the survival rate of primary trigeminal ganglion neurons and promoted the growth of neurites	[130]
2020	Rat	α-MEM + 10% (FBS + P/S + NEAA)	DPSCs-CM	50% DPSCs-CM	PC12 cells	8 d	DPSCs-CM was found to contain neurotrophic factors, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor, which increased the viability and differentiation of PC12 cells and played an important role in axonal growth and survival, proving that DPSCs-CM treatment is a potential cell-free therapy for peripheral nerve repair and has a stronger effect on PC12 cells than DPSCs	[115]

AA: Ascorbic acid; bFGF: Basic fibroblast growth factor; DPSCs-CM: DPSCs-conditioned medium; DMEM: Dulbecco’s modified Eagle medium; FBS: Fetal bovine serum; NTF: Neurotrophic factor; NEAA: Nonessential amino acids; P/S: Penicillin and streptomycin; TGNC: Trigeminal ganglion neuronal cells.