Therapeutic Regeneration Research Articles

Human Beta Cell Regenerative Drug Therapy for Diabetes: Past Achievements and Future Challenges.

A quantitative deficiency of normally functioning insulin-producing pancreatic beta cells is a major contributor to all common forms of diabetes. This is the underlying premise for attempts to replace beta cells in people with diabetes by pancreas transplantation, pancreatic islet transplantation, and transplantation of beta cells or pancreatic islets derived from human stem cells. While progress is rapid and impressive in the beta cell replacement field, these approaches are expensive, and for transplant approaches, limited by donor organ availability. For these reasons, beta cell replacement will not likely become available to the hundreds of millions of people around the world with diabetes. Since the large majority of people with diabetes have some residual beta cells in their pancreata, an alternate approach to reversing diabetes would be developing pharmacologic approaches to induce these residual beta cells to regenerate and expand in a way that also permits normal function. Unfortunately, despite the broad availability of multiple classes of diabetes drugs in the current diabetes armamentarium, none has the ability to induce regeneration or expansion of human beta cells. Development of such drugs would be transformative for diabetes care around the world. This picture has begun to change. Over the past half-decade, a novel class of beta cell regenerative small molecules has emerged: the DYRK1A inhibitors. Their emergence has tremendous potential, but many areas of uncertainty and challenge remain. In this review, we summarize the accomplishments in the world of beta cell regenerative drug development and summarize areas in which most experts would agree. We also outline and summarize areas of disagreement or lack of unanimity, of controversy in the field, of obstacles to beta cell regeneration, and of challenges that will need to be overcome in order to establish human beta cell regenerative drug therapeutics as a clinically viable class of diabetes drugs.

Hypoimmune induced pluripotent stem cell–derived cell therapeutics treat cardiovascular and pulmonary diseases in immunocompetent allogeneic mice

The emerging field of regenerative cell therapy is still limited by the few cell types that can reliably be differentiated from pluripotent stem cells and by the immune hurdle of commercially scalable allogeneic cell therapeutics. Here, we show that gene-edited, immune-evasive cell grafts can survive and successfully treat diseases in immunocompetent, fully allogeneic recipients. Transplanted endothelial cells improved perfusion and increased the likelihood of limb preservation in mice with critical limb ischemia. Endothelial cell grafts transduced to express a transgene for alpha1-antitrypsin (A1AT) successfully restored physiologic A1AT serum levels in mice with genetic A1AT deficiency. This cell therapy prevented both structural and functional changes of emphysematous lung disease. A mixture of endothelial cells and cardiomyocytes was injected into infarcted mouse hearts, and both cell types orthotopically engrafted in the ischemic areas. Cell therapy led to an improvement in invasive hemodynamic heart failure parameters. Our study supports the development of hypoimmune, universal regenerative cell therapeutics for cost-effective treatments of major diseases.

Development of a standardized histopathology scoring system for intervertebral disc degeneration and regeneration in rabbit models-An initiative of the ORSspine section.

BackgroundThe rabbit lumbar spine is a commonly utilized model for studying intervertebral disc degeneration and for the pre‐clinical evaluation of regenerative therapies. Histopathology is the foundation for which alterations to disc morphology and cellularity with degeneration, or following repair or treatment are assessed. Despite this, no standardized histology grading scale has yet been established for the spine field for any of the frequently utilized animal models.AimsThe purpose of this study was to establish a new standardized scoring system to assess disc degeneration and regeneration in the rabbit model.Materials and MethodsThe scoring system was formulated following a review of the literature and a survey of spine researchers. Validation of the scoring system was carried out using images provided by 4 independent laboratories, which were graded by 12 independent graders of varying experience levels. Reliability testing was performed via the computation of intra‐class correlation coefficients (ICC) for each category and the total score. The scoring system was then further refined based on the results of the ICC analysis and discussions amongst the authors.ResultsThe final general scoring system involves scoring 7 features (nucleus pulposus shape, area, cellularity and matrix condensation, annulus fibrosus/nucleus pulposus border appearance, annulus fibrosus morphology, and endplate sclerosis/thickening) on a 0 (healthy) to 2 (severe degeneration) scale. ICCs demonstrated overall moderate to good agreement across graders. An addendum to the main scoring system is also included for use in studies evaluating regenerative therapeutics, which involves scoring cell cloning and morphology within the nucleus pulposus and inner annulus fibrosus.DiscussionOverall, this new scoring system provides an avenue to improve standardization, allow a more accurate comparison between labs and more robust evaluation of pathophysiology and regenerative treatments across the field.ConclusionThis study developed a histopathology scoring system for degeneration and regeneration in the rabbit model based on reported practice in the literature, a survey of spine researchers, and validation testing.

Agent-based model provides insight into the mechanisms behind failed regeneration following volumetric muscle loss injury.

Skeletal muscle possesses a remarkable capacity for repair and regeneration following a variety of injuries. When successful, this highly orchestrated regenerative process requires the contribution of several muscle resident cell populations including satellite stem cells (SSCs), fibroblasts, macrophages and vascular cells. However, volumetric muscle loss injuries (VML) involve simultaneous destruction of multiple tissue components (e.g., as a result of battlefield injuries or vehicular accidents) and are so extensive that they exceed the intrinsic capability for scarless wound healing and result in permanent cosmetic and functional deficits. In this scenario, the regenerative process fails and is dominated by an unproductive inflammatory response and accompanying fibrosis. The failure of current regenerative therapeutics to completely restore functional muscle tissue is not surprising considering the incomplete understanding of the cellular mechanisms that drive the regeneration response in the setting of VML injury. To begin to address this profound knowledge gap, we developed an agent-based model to predict the tissue remodeling response following surgical creation of a VML injury. Once the model was able to recapitulate key aspects of the tissue remodeling response in the absence of repair, we validated the model by simulating the tissue remodeling response to VML injury following implantation of either a decellularized extracellular matrix scaffold or a minced muscle graft. The model suggested that the SSC microenvironment and absence of pro-differentiation SSC signals were the most important aspects of failed muscle regeneration in VML injuries. The major implication of this work is that agent-based models may provide a much-needed predictive tool to optimize the design of new therapies, and thereby, accelerate the clinical translation of regenerative therapeutics for VML injuries.

Tissue engineering and regenerative therapeutics: The nexus of chemical engineering and translational medicine

AbstractSince its emergence nearly 30 years ago with the goal of fabricating replacement human tissues or assisting the body in repairing itself, several advances have been made in the fields of tissue engineering and regenerative medicine. The assembly of living cells into tissues is akin to the scale‐up operation of a chemical or biochemical process with several modules or units affecting the final product. The major modules or units in tissue engineering and regenerative medicine are cells, biodegradable scaffolds, bioreactors, and biomolecules. Each module is analogous to unit operations, where individual units must come together to successfully design engineered tissues for therapeutic and drug discovery applications. Basic principles of biological sciences, chemical engineering, materials chemistry, and polymer processing are frequently employed. More specifically, knowledge about viscous fluid flow, mass transfer, and reaction engineering is essential in tissue engineering. In this review article, we present the nexus between chemical engineering and tissue engineering for the rational design of engineered tissues or injectable cell‐laden hydrogel systems.

Primary Neural Degeneration in Noise-Exposed Human Cochleas: Correlations with Outer Hair Cell Loss and Word-Discrimination Scores.

Animal studies suggest that cochlear nerve degeneration precedes sensory cell degeneration in both noise-induced hearing loss (NIHL) and age-related hearing loss (ARHL), producing a hearing impairment that is not reflected in audiometric thresholds. Here, we investigated the histopathology of human ARHL and NIHL by comparing loss of auditory nerve fibers (ANFs), cochlear hair cells and the stria vascularis in a group of 52 cases with noise-exposure history against an age-matched control group. Although strial atrophy increased with age, there was no effect of noise history. Outer hair cell (OHC) loss also increased with age throughout the cochlea but was unaffected by noise history in the low-frequency region (<2 kHz), while greatly exacerbated at high frequencies (≥2 kHz). Inner hair cell (IHC) loss was primarily seen at high frequencies but was unaffected by noise at either low or high frequencies. ANF loss was substantial at all cochlear frequencies and was exacerbated by noise throughout. According to a multivariable regression model, this loss of neural channels contributes to poor word discrimination among those with similar audiometric threshold losses. The histopathological patterns observed also suggest that, whereas the low-frequency OHC loss may be an unavoidable consequence of aging, the high-frequency loss, which produces the classic down-sloping audiogram of ARHL, may be partially because of avoidable ear abuse, even among those without a documented history of acoustic overexposure.SIGNIFICANCE STATEMENT As regenerative therapeutics in sensorineural hearing loss enter clinical trials, it becomes critical to infer which cochlear pathologies are present in addition to hair cell loss. Here, by analyzing human autopsy material, we show that acoustic injury accelerates age-related primary neural degeneration, but not strial degeneration, neither of which can be inferred from audiometric thresholds. It exacerbates outer hair cell (OHC) loss only in the high-frequency half of the cochlea, suggesting that the apical loss is age-related, whereas the basal loss is partially noise induced, and therefore avoidable. Statistical analysis suggests that neural loss helps explain differences in word-recognition ability among individuals with similar audiometric thresholds. The surprising correlation between neural loss and OHC loss in the cochlea's speech region also implicates neural loss in the well-known decline in word scores as thresholds deteriorate with age.

Optimization of Spheroid Colony Culture and Cryopreservation of Nucleus Pulposus Cells for the Development of Intervertebral Disc Regenerative Therapeutics

After the discovery of functionally superior Tie2-positive nucleus pulposus (NP) progenitor cells, new methods were needed to enable mass culture and cryopreservation to maintain these cells in an undifferentiated state with high cell yield. We used six types of EZSPHERE® dishes, which support spheroid-forming colony culture, and examined NP cell spheroid-formation ability, number, proliferation, and mRNA expression of ACAN, COL1A2, COL2A1, and ANGPT1. Six different types of cryopreservation solutions were examined for potential use in clinical cryopreservation by comparing the effects of exposure time during cryopreservation on cell viability, Tie2-positivity, and cell proliferation rates. The spheroid formation rate was 45.1% and the cell proliferation rate was 7.75 times using EZSPHERE® dishes. The mRNA levels for COL2A1 and ANGPT1 were also high. In cryopreservation, CryoStor10 (CS10) produced ≥90% cell viability and a high proliferation rate after thawing. CS10 had a high Tie2-positive rate of 12.6% after culturing for 5 days after thawing. These results suggest that EZSPHERE enabled colony formation in cell culture without the use of hydrogel products and that CS10 is the best cryopreservation medium for retaining the NP progenitor cell phenotype and viability. Together, these data provide useful information of NP cell-based therapeutics to the clinic.

Chemical induction of neurogenic properties in mammalian Müller glia.

Müller glia (MG), cells that maintain homeostasis in the retina, are dormant stem cells that can regenerate neurons upon injury. However, the regenerative property of MG, which is reproducibly displayed in the lower vertebrates, is not readily observed in the mammals even upon forced expression of regulatory genes or exposure to growth factors. Here, we demonstrate a reproducible unmasking of the neurogenic properties of enriched rodent MG by serial exposure to different combinations of small molecules. The enriched MG, in response to changing culture conditions, silenced glia-specific genes and acquired transcriptional signature of neurons, accompanied by upregulation of genes known to regulate neuronal potential of MG. The MG-derived neurons expressed immunoreactivities corresponding to neuronal proteins and displayed electrophysiological features of immature neurons. Our study presents a proof of principle of pharmacological activation of neurogenic properties of mammalian MG, which may be utilized for therapeutic regeneration.

Intervertebral disc degeneration and regeneration: a motion segment perspective.

Back and neck pain have become primary reasons for disability and healthcare spending globally. While the causes of back pain are multifactorial, intervertebral disc degeneration is frequently cited as a primary source of pain. The annulus fibrosus (AF) and nucleus pulposus (NP) subcomponents of the disc are common targets for regenerative therapeutics. However, disc degeneration is also associated with degenerative changes to adjacent spinal tissues, and successful regenerative therapies will likely need to consider and address the pathology of adjacent spinal structures beyond solely the disc subcomponents. This review summarises the current state of knowledge in the field regarding associations between back pain, disc degeneration, and degeneration of the cartilaginous and bony endplates, the AF-vertebral body interface, the facet joints and spinal muscles, in addition to a discussion of regenerative strategies for treating pain and degeneration from a whole motion segment perspective.

Antigen-driven PD-1+ TOX+ BHLHE40+ and PD-1+ TOX+ EOMES+ T lymphocytes regulate juvenile idiopathic arthritis in situ.

T lymphocytes accumulate in inflamed tissues of patients with chronic inflammatory diseases (CIDs) and express pro-inflammatory cytokines upon re-stimulation in vitro. Further, a significant genetic linkage to MHC genes suggests that T lymphocytes play an important role in the pathogenesis of CIDs including juvenile idiopathic arthritis (JIA). However, the functions of T lymphocytes in established disease remain elusive. Here we dissect the transcriptional and the clonal heterogeneity of synovial T lymphocytes in JIA patients by single-cell RNA sequencing combined with T cell receptor profiling on the same cells. We identify clonally expanded subpopulations of T lymphocytes expressing genes reflecting recent activation by antigen in situ. A PD-1+ TOX+ EOMES+ population of CD4+ T lymphocytes expressed immune regulatory genes and chemoattractant genes for myeloid cells. A PD-1+ TOX+ BHLHE40+ population of CD4+ , and a mirror population of CD8+ T lymphocytes expressed genes driving inflammation, and genes supporting B lymphocyte activation in situ. This analysis points out that multiple types of T lymphocytes have to be targeted for therapeutic regeneration of tolerance in arthritis.

Diagnostic and Therapeutic Applications of Extracellular Vesicles in Interstitial Lung Diseases.

Interstitial lung diseases (ILDs) are chronic irreversible pulmonary conditions with significant morbidity and mortality. Diagnostic approaches to ILDs are complex and multifactorial. Effective therapeutic interventions are continuously investigated and explored with substantial progress, thanks to advances in basic understanding and translational efforts. Extracellular vesicles (EVs) offer a new paradigm in diagnosis and treatment. This leads to two significant implications: new disease biomarker discovery that enables reliable diagnosis and disease assessment and the development of regenerative medicine therapeutics that target fibroproliferative processes in diseased lung tissue. In this review, we discuss the current understanding of the role of diseased tissue-derived EVs in the development of interstitial lung diseases, the utility of these EVs as diagnostic and prognostic tools, and the existing therapeutic utility of EVs. Furthermore, we review the potential therapeutic application of EVs derived from various cellular sources.

The neurosphere assay: an effective in vitro technique to study neural stem cells.

The neurosphere assay: an effective in vitro technique to study neural stem cells.

Emerging biogenesis technologies of extracellular vesicles for tissue regenerative therapeutics

Extracellular vesicles (EVs), including exosomes, carry the genetic packages of RNA, DNA, and proteins and are heavily involved in cell-cell communications and intracellular signalings. Therefore, EVs are spotlighted as therapeutic mediators for the treatment of injured and dysfunctional tissues as well as biomarkers for the detection of disease status and progress. Several key issues in EVs, including payload content and bioactivity, targeting and bio-imaging ability, and mass-production, need to be improved to enable effective therapeutics and clinical translation. For this, significant efforts have been made recently, including genetic modification, biomolecular and chemical treatment, application of physical/mechanical cues, and 3D cultures. Here we communicate those recent technological advances made mainly in the biogenesis process of EVs or at post-collection stages, which ultimately aimed to improve the therapeutic efficacy in tissue healing and disease curing and the possibility of clinical translation. This communication will help tissue engineers and biomaterial scientists design and produce EVs optimally for tissue regenerative therapeutics.

Controllable ligand spacing stimulates cellular mechanotransduction and promotes stem cell osteogenic differentiation on soft hydrogels

Hydrogels with tunable mechanical properties have provided a tremendous opportunity to regulate stem cell differentiation. Hydrogels with osteoid (about 30–40 kPa) or higher stiffness are usually required to induce the osteogenic differentiation of mesenchymal stem cells (MSCs). It is yet difficult to achieve the same differentiation on very soft hydrogels, because of low environmental mechanical stimuli and restricted cellular mechanotransduction. Here, we modulate cellular spatial sensing of integrin-adhesive ligands via quasi-hexagonally arranged nanopatterns to promote cell mechanosensing on hydrogels having low stiffness (about 3 kPa). The increased interligand spacing has been shown to regulate actomyosin force loading to recruit extra integrins on soft hydrogels. It therefore activates mechanotransduction and promotes the osteogenic differentiation of MSCs on soft hydrogels to the level comparable with the one observed on osteoid stiffness. Our work opens up new possibilities for the design of biomaterials and tissue scaffolds for regenerative therapeutics.

Abstract 15756: Vascular Guidance of Cardiomyocyte Proliferation During Growth and Regeneration

Introduction: Stimulating cardiomyocyte (CM) proliferation is a major strategy for achieving therapeutic heart regeneration. However, heart regeneration requires coordinated interactions of multiple cell types. Because a hallmark of advanced heart failure is vascular rarefaction, the requirement of cardiac endothelial cells (CECs) for cardiac growth and regeneration is of particular importance. Hypothesis: We hypothesized that CECs are required for CM proliferation during growth and regeneration. Methods and Results: We performed a large-scale histologic assessment of neonatal mouse hearts and found the rate of CEC proliferation to shadow CM proliferation over the first 10 days of life. Using a nearest neighbor analysis, we found the fraction of proliferating CECs to be significantly enriched around cycling CMs compared to non-cycling CMs, suggesting that CEC and CM expansion are coupled within a myovascular niche. Single cell sequencing of neonatal mouse hearts after cryoinjury revealed that a majority of these proliferating CECs also express Vegfr2 . To functionally link CEC and CM proliferation, we generated Cdh5-CreER T2 ; Vefgr2 flox/flox mice to genetically delete Vegfr2 from CECs. Compared to mice with intact Vegfr2 , loss of Vegfr2 from CECs in neonatal mice leads to loss of CECs and severely dampens CM proliferation by 4 days (7.01±0.88% vs 0.39±0.35%, p = 7.4x10-4, n = 9),. Interestingly, CM proliferation is attenuated when Vegfr2 is deleted from CECs despite an increase of hypoxia indicators in CMs, signifying that hypoxia-induced CM proliferation is dependent on CECs. In contrast to CEC depletion, treatment of cryoinjured neonatal hearts with AAV encoding the master angiogenic factor, Vegfa can enhance heart regeneration with increased CM cycling in the borderzone (12.6±2.2% vs 5.4±0.4%, p = 0.02, n = 8), reduced scarring of the left ventricle (3.4±1.4% vs 7.6±1.2%, p = 03, n = 16), and improved fractional shortening (51.7±2.5% vs 36.7±4.3%, p = 0.007, n = 14). Conclusions: CEC and CM expansion are spatiotemporally coupled in a myovascular niche during cardiac growth. CECs play a critical role to support CM proliferation and are likely to provide instructive cues that may be leveraged for therapeutic heart regeneration.

Nano-Biomaterials for the Delivery of Therapeutic and Monitoring Cues for Aortic Diseases.

The aorta is the largest artery in the body, so any diseases or conditions which could cause damage to the aorta would put patients at considerable and life-threatening risk. In the management of aortic diseases, the major treatments include drug therapy, endovascular treatment, and surgical treatment, which are of great danger or with a poor prognosis. The delivery of nano-biomaterials provides a potential development trend and an emerging field where we could monitor patients’ conditions and responses to the nanotherapeutics. One of the putative applications of nanotechnology is ultrasensitive monitoring of cardiovascular markers by detecting and identifying aneurysms. Moreover, the use of nanosystems for targeted drug delivery can minimize the systemic side effects and enhance drug positioning and efficacy compared to conventional drug therapies. This review shows some examples of utilizing nano-biomaterials in in vitro organ and cell culture experiments and explains some developing technologies in delivering and monitoring regenerative therapeutics.

CIRM tools and technologies: Breaking bottlenecks to the development of stem cell therapies.

The California Institute for Regenerative Medicine (CIRM) has a mission to accelerate stem cell treatments to patients with unmet medical needs. This perspective describes successful examples of work funded by CIRM's New Cell Lines and Tools and Technologies Initiatives, which were developed to address bottlenecks to stem cell research and translation. The tools developed through these programs evolved from more discovery‐oriented technologies, such as disease models, differentiation processes, and assays, to more translation focused tools, including scalable good manufacturing processes, animal models, and tools for clinical cell delivery. These tools are available to the research community and many are facilitating translation of regenerative therapeutics today.

Microenvironment stiffness requires decellularized cardiac extracellular matrix to promote heart regeneration in the neonatal mouse heart

The transient period of regeneration potential in the postnatal heart suggests molecular changes with maturation influence the cardiac response to damage. We have previously demonstrated that injury and exercise can stimulate cardiomyocyte proliferation in the adult heart suggesting a sensitivity to exogenous signals. Here, we consider whether exogenous fetal ECM and mechanically unloading interstitial matrix can drive regeneration after myocardial infarction (MI) surgery in low-regenerative hearts of day5 mice. Compared to controls, exogenous fetal ECM increases cardiac function and lowers fibrosis at 3 weeks post-injury and this effect can be augmented by softening heart tissue. In vitro experiments support a mechano-sensitivity to exogenous ECM signaling. We tested potential mechanisms and observed that fetal ECM increases nuclear YAP localization which could be enhanced by pharmacological stabilization of the cytoskeleton. Blocking YAP expression lowered fetal ECM effects though not completely. Lastly we observed mechanically unloading heart interstitial matrix increased agrin expression, an extracellular node in the YAP signaling pathway. Collectively, these data support a combined effect of exogenous factors and mechanical activity in altering agrin expression, cytoskeletal remodeling, and YAP signaling in driving cardiomyocyte cell cycle activity and regeneration in postnatal non-regenerative mice. Statement of SignificanceWith the purpose of developing regenerative strategies, we investigate the influence of the local niche on the cardiac injury response. We conclude tissue stiffness, as anticipated in aging or disease, impairs regenerative therapeutics. Most novel, mechanical unloading facilitates enhanced cardiac regeneration only after cells are pushed into a permissive state by fetal biomolecules. Specifically, mechanical unloading appears to increase extracellular agrin expression that amplifies fetal-stimulation of nuclear YAP signaling which correlates with observed increases of cell cycle activity in cardiomyocytes. The results further suggest the cytoskeleton is critical to this interaction between mechanical unloading and independently actived YAP signaling. Using animal models, tissue explants, and cells, this work indicates that local mechanical stimuli can augment proliferating-permissive cardiomyocytes in the natural cardiac niche.

Monocyte mimics improve mesenchymal stem cell-derived extracellular vesicle homing in a mouse MI/RI model

Stem cell-derived extracellular vesicles (EVs) have been demonstrated to be effective in heart repair and regeneration post infarction. However, the poor homing efficiency and low yields of these therapeutics remain the major obstacles before they can be used in the clinic. To improve the delivery efficiency of EVs to ischemia-injured myocardium, we modified mesenchymal stem cell (MSC)-derived EVs with monocyte mimics through the method of membrane fusion. Monocyte mimic-bioinspired MSC-EVs (Mon-Exos) exhibited enhanced targeting efficiency to injured myocardium by mimicking the recruitment feature of monocytes after MI/RI, thus contributing to these exclusive adhesive molecules on monocyte mimics, particularly the Mac1/LFA1-ICAM-1 interaction. Through this strategy, Mon-Exos were shown to promote endothelial maturation during angiogenesis and modulate macrophage subpopulations after MI/RI, consistent with MSC-Exos biofunctions, and eventually improve therapeutic outcomes in cardiac function and pathohistology changes after treatments in a mouse MI/RI model. Ultimately, this strategy might provide us with a better way to assess the effects of stem cell EVs and offer additional techniques to help clinicians better manage regenerative therapeutics for ischemic heart diseases.

Revisiting the Regenerative Therapeutic Advances Towards Erectile Dysfunction.

Erectile dysfunction (ED) is an inability to attain or maintain adequate penile erection for successful vaginal intercourse, leading to sexual and relationship dissatisfaction. To combat ED, various surgical and non-surgical approaches have been developed in the past to restore erectile functions. These therapeutic interventions exhibit significant impact in providing relief to patients; however, due to their associated adverse effects and lack of long-term efficacy, newer modalities such as regenerative therapeutics have gained attention due to their safe and prolonged efficacy. Stem cells and platelet-derived biomaterials contained in platelet-rich plasma (PRP) are thriving as some of the major therapeutic regenerative agents. In recent years, various preclinical and clinical studies have evaluated the individual, as well as combined of stem cells and PRP to restore erectile function. Being rich in growth factors, chemokines, and angiogenic factors, both stem cells and PRP play a crucial role in regenerating nerve cells, myelination of axons, homing and migration of progenitor cells, and anti-fibrosis and anti-apoptosis of damaged cavernous nerve in corporal tissues. Further, platelet-derived biomaterials have been proven to be a biological supplement for enhancing the proliferative and differentiation potential of stem cells towards neurogenic fate. Therefore, this article comprehensively analyzes the progresses of these regenerative therapies for ED.