Programmed cell death in stem cell-based therapy: Mechanisms and clinical applications

Table 1 Summary of programmed cell deaths in stem cell-based therapy

Disease	SCs	Therapy models	Therapeutic effects	PCDs in SCs	Ref.
Myocardial infarction	MSCs	Canine; porcine; mice; human	Inducing cardiac regeneration; increasing angiogenesis; repair by differentiating into cardiomyocytes	Apoptosis, autophagy, pyroptosis	[46-48]
	iPSCs	Porcine; murine; rats; mice; non-human primates	Showing heart regeneration potential; regenerating the injured tissues; promoting a cardiomyogenic and angiogenic response	Apoptosis, autophagy, ferroptosis	[48,49]
	ESCs	Non-human primates	Showing heart regeneration potential; increasing angiogenic differentiation	Apoptosis, autophagy, pyroptosis	[48,50]
Intracerebral hemorrhage	MSCs	Rats; primates; human	Repairing via differentiating into neurons or neuron-like cells; promoting axonal regeneration, neurogenesis, and angiogenesis	Apoptosis, autophagy, pyroptosis	[51-54]
	NSCs	Mice, rats	Differentiating into neurons or glial cells; promoting neurogenesis and angiogenesis; promoting regeneration	Apoptosis, autophagy	[51,55-57]
	ESCs	Rats	Differentiating into neurons or glial cells; promoting neurogenesis and angiogenesis	Apoptosis, autophagy, pyroptosis	[51,58,59]
	iPSCs	Rats	Differentiating into neuroepithelium-like/neuroepithelioid SCs and neural cells; promoting neurogenesis and angiogenesis	Apoptosis, autophagy, ferroptosis	[51,60-62]
Corneal reconstruction	LSCs	Human	Regenerating the corneal epithelium; differentiating into cells of the corneal epithelium	Apoptosis.	[19]
	MSCs	Mice; rats; rabbits; human	Regenerating the corneal epithelium and corneal stroma; angiogenesis	Apoptosis, autophagy, pyroptosis	[63]
Neurodegenerative disorders of the gastrointestinal tract	ESCs	Mice	Differentiating into enteric neuronal and glial cells	Apoptosis, autophagy, pyroptosis	[20,64]
	iPSCs	Rats, mice	Differentiating into neural and glial cells	Apoptosis, autophagy, ferroptosis	[20,65]
	CNS-NSCs	Mice	Differentiating into neurons; regenerating and repairing ENS	Apoptosis, autophagy	[20,66,67]
	ENSCs	Mice; rats	Stimulating a local regenerative response; regenerating and repairing ENS; differentiating into new neurons	Apoptosis, autophagy	[20,68,69]
Diabetic cardiomyopathy	MSCs	Mice; rats	Promoting angiogenesis; regenerating tissues; differentiating into cardiomyocytes and vasculature cells	Apoptosis, autophagy, pyroptosis	[21,70]
	EPCs	Rats	Differentiating into endothelial cells to form new blood vessels and promoting neovascularization	Apoptosis	[70,71]
	CSCs/CPCs	Rats	Differentiating into newborn cardiomyocyte; promoting heart regeneration	Apoptosis	[70,72]
	iPSCs	Rats; mice	Attenuating oxidative stress and fibrosis; diminishing pro-oxidant expression and enhancing antioxidant (catalase and MnSOD) concentration; promoting heart regeneration	Apoptosis, autophagy, ferroptosis	[70,73]
Diabetic retinopathy	ASCs	Rats; mice	Promoting angiogenesis; improving ischemia; offering protection against nerve damage; differentiating into photoreceptor and glial-like cells in the retina	Apoptosis	[74-77]
	HSCs	Murine; rats	Promoting angiogenesis	Apoptosis, autophagy	[74,78]
	BM-MSCs	Murine; rats; mice	Differentiating into retinal glial cells; stimulating angiogenesis; promoting resident neural progenitors to regenerate neuro-retinal tissue	Apoptosis, autophagy, pyroptosis	[74,79,80]
	iPSCs	Rats; mice	Differentiating into cells expressing features of retinal pigment epithelial cells, retinal progenitor cells, and retinal ganglion cells, and slowing down retinal degeneration	Anti-apoptosis, autophagy, ferroptosis	[75,81]
Neurological disorders	NSCs	Mice, rats, monkeys, pigs, human	Differentiating into neurons and supporting glial cells; releasing angiogenic factors to promote local tissue regeneration	Apoptosis, autophagy	[82-85]
	HSCs	Human	Promoting cell survival; stimulating proliferation and migration of NSCs; inducing regeneration of damaged brain cells; promoting angiogenesis	Apoptosis, autophagy	[82,86]
	MSCs	Human	Promoting neuronal regeneration; promoting angiogenesis	Apoptosis, autophagy, pyroptosis	[82,86]
Diabetes	ESCs	Mice, rats	Differentiating into cluster of insulin producing beta cells	Apoptosis, autophagy, pyroptosis	[87-89]
	Hepatic and intestinal stem cells	Mice	Differentiating into beta cells in response to high glucose concentration	Apoptosis	[87,90]
	Spleen stem cells	Mice	Differentiating into insulin secreting beta cells; regenerating islet	Apoptosis	[87,91]
	HSCs	Mice	Differentiating into beta cells and vascular endothelial cells of the pancreas; inducing beta cell regeneration from the host cells residing in pancreas	Apoptosis, autophagy	[87,92]

SC: Stem cell; MSCs: Mesenchymal stem cells; NSCs: Neural stem cells; ESCs: Embryonic stem cells; iPSCs: Induced pluripotent stem cells; LSCs: Limbal stem cells; CNS-NSCs: CNS-derived NSCs; ENSCs: Enteric neural stem cells; CSCs/CPC: Cardiac stem/progenitor cells; ASCs: Adipose stem cells; HSCs: Hematopoietic stem cells; BM-MSCs: Bone marrow derived mesenchymal stem cells; ENS: Enteric nervous system; EPCs: Endothelial progenitor cells; PCD: Programmed cell death.

Table 2 Molecular mechanisms and therapeutic targets of programmed cell deaths in stem cells

PCDs	SCs	Molecular pathways of PCDs	Therapeutic target(s)	Therapeutic effects	Ref.
Apoptosis	hESCs	Mitochondrial priming and p53 signaling pathway	Bcl-2	Preventing damaged cells from compromising the genomic integrity of the population	[119]
	HSCs	ASPP1 stimulated p53 signaling pathway	ASPP1, RUNX1	Preventing hematological malignancies	[120]
	ISCs	ARTS/XIAP/caspase 9 axis	XIAP	Controlling ISC numbers and preventing the propagation of abnormal progeny	[121]
	MSCs	p38 MAPK regulated early apoptosis while JNK regulated late apoptosis	p38	Protecting MSCs from oxidative stress damage	[38]
	NSCs	p38 MAPK signaling	TNF-α, p38	Impairing cell viability, decreasing therapeutic effects	[122]
Autophagy	iPSCs	AMPK/mTOR/ULK1 complex/PI3K complex/conjugation cascade complexes with LC3 and Atg9 during macroautophagy;KFERQ domain/Hsc 70/LAMP2A during CMA	LC3	Removing unnecessary or dysfunctional components	[123]
	HSCs	type III PI3K mammalian Atg6/PIP3/(Atg12-Atg5-Atg16) or (Atg4/LC3-I/Atg7/Atg3/LC3-II/PE) axis	LC3-II	Recycling cytoplasmic constituents and restoring metabolic homeostasis, and maintaining cells survival under harsh conditions	[124]
	NSCs	PI3K-AKT-mTOR/ULK1/the class III PI3-kinase-Beclin1 complex/PI3/PI3P/ the complex of Atg12–Atg5–Atg16L1/LC3-I/LC3-II axis	mTOR	Being involved in modulation of the embryonic neurogenesis as well as the injury repair of adult brain	[125]
	MSCs	PI3K/AKT/mTOR/ULK1/the class III PI3-kinase-Beclin1 complex/PI3/PI3P/the complex of Atg12–Atg5–Atg16L1/LC3-I/LC3-II axis	AKT, mTOR	Eliminating damaged organelles and biomacromolecules to maintain cellular homeostasis	[126,127]
	ESCs	AMPK/ mTORC1/ULK1 axis	Atg5, Atg12	Maintaining the undifferentiated state of ESCs in vitro	[128]
Necroptosis	ISCs	ZBP1/RIP3/MLKL axis	ZBP1	Disrupting homeostasis of the epithelial barrier and promoting bowel inflammation	[35,129]
	SSCs	RIP1 signaling pathway	RIP1	Using Nec-1 to target RIP1 for reducing both necroptosis and apoptosis, which benefits for recovery rate and proliferation potential	[130]
	NPSCs	RIPK1/RIPK3/MLKL axis	HSP90	Protecting SCs from PCD via alleviating mitochondrial dysfunction (mitochondrial membrane potential loss and ATP depletion) and oxidative stress (production of mitochondrial ROS), cellular total ROS and MDA, and downregulation of superoxide dismutase	[131]
Pyroptosis	MSCs	Exosome/circHIPK3/ FOXO3a axis	circHIPK3	Preventing pyroptosis and repairing ischemic muscle injury through a novel exosome	[132]
	ESCs	Caspase-1 signaling pathway	N/A	Embryonic stem cell-derived exosomes inhibit doxorubicin-induced pyroptosis	[133]
Ferroptosis	NPCs and IPSCs	Ferritin/ROS/lipid peroxidation axis	NCOA4, p53	Decreasing stem cells and triggering neuronal death	[134]

ISCs: Intestinal stem cells; iPCs: Induced pluripotent stem cells; HSCs: Hematopoietic stem cells; ESCs: Embryonic stem cells; NSCs: Neural stem cells; MSCs: Mesenchymal stem cells; EPCs: Endothelial progenitor cells; CPCs: Cardiac progenitor cells; IPSC: Pluripotent stem cells; ZBP1: Z-DNA-binding protein 1; RIP3: Receptor-interacting serine/threonine kinase 3; MLKL: Mixed lineage kinase domain like protein; PUMA: p53 upregulated modulator of apoptosis; NOXA: Known as PMAIP1, phorbol-12-myristate-13-acetate-induced protein 1; Bax: Bcl-2 associated X protein; Bak: Bcl-2 antagonist/killer 1 protein; cyt c: Cytochrome C; Apaf-1: Apoptosis protease activating factor-1; casp: Caspase; FADD: Fas-associated death domain; Bcl-2: B-cell lymphoma 2; AMPK: AMP-activated protein kinase; mTOR: Mammalian target of rapamycin; ULK1: Unc-51-like kinase complex; ROS: Reactive oxygen species; MDA: Malondialdehyde; GPX4: Glutathione peroxidase 4; circHIPK3: One of the most abundant circRNA in muscle; FOXO3a: A transcription factor of the O subclass of the forkhead family; LncRNA: Long non-coding RNAs; KLF3-AS1: Localize at chromosome 4p14 according to the exocarta database; mTOR: Mammalian target of rapamycin; ULK1: Atg1/unc-51-like kinase; LC3: Light chain 3; PI3K: Beclin-1/class III phosphatidylinositol 3-kinase; CMA: Chaperone-mediated autophagy; Hsc 70: Heat shock cognate71 kDa protein; LAMP2A: Lysosomal-associated membrane protein type 2; Atg: Autophagyassociated gene; Atg6: Vps34/Beclin-1; PIP3: Phosphatidylinositol (3,4,5) P3; PE: Phosphatidyl ethanolamine; SSCs: Spermatogonial stem cells; Nec-1: Necrostatin-1, a necroptosis inhibitor; NPSCs: Nucleus pulposus-derived stem/progenitor cells; HSP90: Heat shock protein 90; ROS: Reactive oxygen species; PCD: Programmed cell death.

Table 3 Strategies to enhance stem cell transplantation therapy

Strategy	Method	Target	Effects	Molecular mechanisms	Ref.
Preconditioning	Short repeated ischemia/reperfusion	ESCs	Enhancing the tolerance of subsequent prolonged lethal ischemia	Promoting the expression of trophic factors, inducing the release and activation of PKC, PKB, or Akt, NF-κB and Src protein tyrosine kinases, and subsequently upregulating COX-2, iNOS, HO-1, Mn superoxide dismutase, aldose reductase, and antiapoptotic genes	[210-212]
	Hypoxia	MSCs	Promoting mesenchymal stem cell migration and survival	Increasing the expression of lncRNA-p21, HIF-1α, and CXCR4/7(both were chemokine SDF-1 receptors)	[213]
		CSCs	Promoting survival and cardiogenic differentiation	Inducing the activation of the HIF-1α/apelin/APJ axis	[214]
		NSCs	Promoting survival and neuroprotective properties, and facilitating functional recovery in vivo	Upregulating HIF1-α and HIF target genes such as EPO and VEGF and neurotrophic, and growth factors	[215]
	Hydrogen peroxide preconditioning	BMSCs	Improving the therapeutic potential for wound healing	Upregulating cyclin D1, SDF-1, and its receptors CXCR4/7 expression, and activating the PI3K/Akt/mTOR pathway, but inhibiting the expression of p16 and GSK-3β	[216]
	Nitric oxide donor preconditioning	hCSCs	Enhancing survival	Upregulating phosphorylation of NRF2, NFκB, STAT3, ERK, and AKT, as well as increasing the protein expression of HO-1 and COX2	[217]
	Heat shocking	MSCs	Promoting migration	Triggering the activation of ERK and PI3K/Akt signaling pathways via HSP90	[218]
Pretreatment	Oxytocin	MSCs	Antiapoptosis and cell protection	Increasing the expression of Akt and phospho-ERK1/2 proteins, rapid calcium mobilization, and upregulation of antiapoptotic and angiogenic genes including HSP27/32/70, TIMP-1/2/3, VEGF, thrombospondin, and matrix metalloproteinase-2	[219]
	Minocycline	NSCs	Increasing the capacity of migration, proliferation, and differentiation to improve neurological recovery	Increasing the expression of Nrf2	[220,221]
	Melatonin	MSCs	Inducing fewer fibrotic damage	Downregulating the levels of TNF-α, TGF-β, and α-SMA, and upregulating the expression of E-cadherin	[222]
	Extremely low-level lasers	MSCs	Enhancing the migration of MSCs; promoting the proliferation rate of SCs	Allowing the FAK and ERK1/2 pathways and increasing PDGF and HGF; inducing the up-regulation of mitochondrial ROS and NO	[223,224]
Genetic strategies	Overexpressing pro-survival factors	hNSCs	Improving short- and long-term survival	Overexpression of Bcl-2, Bcl-xl, Hif1a, or/and Akt1	[225]
	Genetic modification	MSCs	Potentiating MSC survival	Overexpression of ERBB4 and ILK	[226]
3D technology	Hydrogels mimicking	MSCs, ESCs, EPCs	Role in stem cell differentiation, changing matrix stiffness, mechanical stress and strain, nonlinear elastic, microenvironments and viscoelastic microenvironments	N/A	[227]
Co-transplantation	Co-transplantation of MSCs and HSCs	MSCs HSCs	Enhancing therapeutic effects	N/A	[228]

ESCs: Embryonic stem cells; NSCs: Neural stem cells; MSCs: Mesenchymal stem cells; HSCs: Hematopoietic stem cells; EPCs: Endothelial progenitor cells; hNSCs: Human neural stem cells; SCs: Stem cells; Hsp70/90: Heat shock protein 70/90; ERK: Extracellular regulated protein kinases; Nrf2: Nuclear factor erythroid 2; TNF: Tumor necrosis factor; TGF: Tumor growth factor; SMA: Smooth muscle actin; HGF: Hepatocyte growth factor; ROS: Reactive oxygen species; Bcl-2: B-cell lymphoma 2; ERBB4: Erb-b2 receptor tyrosine kinase 4; ILK: Integrin-linked kinase; SDF-1: Stromal-derived factor-1; EPO: Erythropoietin; VEGF: Vascular endothelial growth factor; TIMP: Tissue inhibitor of metalloproteinase; PDGF: Platelet-derived growth factor.