Msh homeobox 1 (Msx1)- and Msx2-overexpressing bone marrow-derived mesenchymal stem cells resemble blastema cells and enhance regeneration in mice

Mechanisms, pathways and strategies for rejuvenation through epigenetic reprogramming

Over the past decade, there has been a dramatic increase in efforts to ameliorate aging and the diseases it causes, with transient expression of nuclear reprogramming factors recently emerging as an intriguing approach. Expression of these factors, either systemically or in a tissue-specific manner, has been shown to combat age-related deterioration in mouse and human model systems at the cellular, tissue and organismal level. Here we discuss the current state of epigenetic rejuvenation strategies via partial reprogramming in both mouse and human models. For each classical reprogramming factor, we provide a brief description of its contribution to reprogramming and discuss additional factors or chemical strategies. We discuss what is known regarding chromatin remodeling and the molecular dynamics underlying rejuvenation, and, finally, we consider strategies to improve the practical uses of epigenetic reprogramming to treat aging and age-related diseases, focusing on the open questions and remaining challenges in this emerging field.

A bioscaffold of decellularized whole osteochondral sheet improves proliferation and differentiation of loaded mesenchymal stem cells in a rabbit model

As a Natural decellularized extracellular matrix, osteochondral tissue is the best scaffold for the restoration of osteoarthritis defects. Bioscaffolds have the most similarly innate properties like biomechanical properties and the preserved connection of the bone-to-cartilage border. Although, their compacity and low porosity particularly, are proven to be difficulties of decellularization and cell penetration. This study aims to develop a new bioscaffold of decellularized osteochondral tissue (DOT) that is recellularized by bone marrow-derived mesenchymal stem cells (BM-MSCs), as a biphasic allograft, which preserved the interface between the cartilage section and subchondral bone of the joint. Whole osteochondral tissues of rabbit knee joints were sheeted in cartilaginous parts in 200-250 µm sections while connected to the subchondral bone and then fully decellularized. The BM-MSCs were seeded on the scaffolds in vitro; some constructs were subcutaneously implanted into the back of the rabbit. The cell penetration, differentiation to bone and cartilage, viability, and cell proliferation in vitro and in vivo were evaluated by qPCR, histological staining, MTT assay, and immunohistochemistry. DNA content analysis and SEM assessments confirmed the decellularization of the bioscaffold. Then, histological and SEM evaluations indicated that the cells could successfully penetrate the bone and cartilage lacunas in implanted grafts. MTT assay confirmed cell proliferation. Prominently, gene expression analysis showed that seeded cells differentiated into osteoblasts and chondrocytes in both bone and cartilage sections. More importantly, seeded cells on the bioscaffold started ECM secretion. Our results indicate that cartilage-to-bone border integrity was largely preserved. Additionally, ECM-sheeted DOT could be employed as a useful scaffold for promoting the regeneration of osteochondral defects.

Chemical reprogramming for cell fate manipulation: Methods, applications, and perspectives

Chemical reprogramming offers an unprecedented opportunity to control somatic cell fate and generate desired cell types including pluripotent stem cells for applications in biomedicine in a precise, flexible, and controllable manner. Recent success in the chemical reprogramming of human somatic cells by activating a regeneration-like program provides an alternative way of producing stem cells for clinical translation. Likewise, chemical manipulation enables the capture of multiple (stem) cell states, ranging from totipotency to the stabilization of somatic fates in vitro. Here, we review progress in using chemical approaches for cell fate manipulation in addition to future opportunities in this promising field.

Chemical-induced epigenome resetting for regeneration program activation in human cells

Human somatic cells can be reprogrammed to pluripotent stem cells by small molecules through an intermediate stage with a regeneration signature, but how this regeneration state is induced remains largely unknown. Here, through integrated single-cell analysis of transcriptome, we demonstrate that the pathway of human chemical reprogramming with regeneration state is distinct from that of transcription-factor-mediated reprogramming. Time-course construction of chromatin landscapes unveils hierarchical histone modification remodeling underlying the regeneration program, which involved sequential enhancer recommissioning and mirrored the reversal process of regeneration potential lost in organisms as they mature. In addition, LEF1 is identified as a key upstream regulator for regeneration gene program activation. Furthermore, we reveal that regeneration program activation requires sequential enhancer silencing of somatic and proinflammatory programs. Altogether, chemical reprogramming resets the epigenome through reversal of the loss of natural regeneration, representing a distinct concept for cellular reprogramming and advancing the development of regenerative therapeutic strategies.

Disruption of the Gut Microbiota Confers Cisplatin Resistance in Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is the leading cause of gynecologic cancer death. Despite initial responses to intervention, up to 80% of patient tumors recur and require additional treatment. Retrospective clinical analysis of patients with ovarian cancer indicates antibiotic use during chemotherapy treatment is associated with poor overall survival. Here, we assessed whether antibiotic (ABX) treatment would impact growth of EOC and sensitivity to cisplatin. Immunocompetent or immunocompromised mice were given untreated control or ABX-containing (metronidazole, ampicillin, vancomycin, and neomycin) water prior to intraperitoneal injection with EOC cells, and cisplatin therapy was administered biweekly until endpoint. Tumor-bearing ABX-treated mice exhibited accelerated tumor growth and resistance to cisplatin therapy compared with control treatment. ABX treatment led to reduced apoptosis, increased DNA damage repair, and enhanced angiogenesis in cisplatin-treated tumors, and tumors from ABX-treated mice contained a higher frequency of cisplatin-augmented cancer stem cells than control mice. Stool analysis indicated nonresistant gut microbial species were disrupted by ABX treatment. Cecal transplants of microbiota derived from control-treated mice was sufficient to ameliorate chemoresistance and prolong survival of ABX-treated mice, indicative of a gut-derived tumor suppressor. Metabolomics analyses identified circulating gut-derived metabolites that were altered by ABX treatment and restored by recolonization, providing candidate metabolites that mediate the cross-talk between the gut microbiome and ovarian cancer. Collectively, these findings indicate that an intact microbiome functions as a tumor suppressor in EOC, and perturbation of the gut microbiota with ABX treatment promotes tumor growth and suppresses cisplatin sensitivity.

SIGNIFICANCE

Restoration of the gut microbiome, which is disrupted following antibiotic treatment, may help overcome platinum resistance in patients with epithelial ovarian cancer. See related commentary by Hawkins and Nephew, p. 4511.

Regulation of feather follicle development and Msx2 gene SNP degradation in Hungarian white goose

BACKGROUND

Hungarian white goose has excellent down production performance and was introduced to China in 2010. The growth and development of feather follicles has an important impact on down production. Goose feather follicles can be divided into primary and secondary feather follicles, both of which originate in the embryonic stage. Msx2 (Msh Homeobox 2) plays a regulatory role in tissues and organs such as eyes, teeth, bones and skin. However, its regulatory mechanism on goose feather follicles development remains unclear.

RESULTS

Msx2 gene first increased, then decreased and increased at the end (E13, E18, E23, E28) during embryonic feather follicle development, and the expression level was the highest at E18. The pEGFP-N1-Msx2 overexpression vector and si-Msx2 siRNA vector were constructed to transfect goose embryo dermal fibroblasts. The results showed that the cell viability of ov-Msx2 group was significantly increased, and the gene expression levels of FGF5 and TGF-β1 genes were significantly down-regulated (P < 0.05), the expressions of PCNA, Bcl2, CDK1, FOXN1 and KGF genes were significantly up-regulated (P < 0.05). After transfection of siRNA vector, the cell viability of the si-Msx2 group was significantly decreased (P < 0.01) compared with the si-NC group. TGF-β1 expression was significantly up-regulated (P < 0.05), FGF5 expression was extremely significantly up-regulated (P < 0.01), while PCNA, Bcl2, CDK1, FOXN1 and KGF gene expression was significantly down-regulated (P < 0.05). High-throughput sequencing technology was used to mine the exon SNPs of Msx2. A total of 11 SNP loci were screened, four of the SNPs located in exon 1 were missense mutations. The feather follicle diameter of the GC genotype at the G78C site is significantly larger than that of the other two genotypes.

CONCLUSIONS

Msx2 maybe inhibit the apoptosis of goose dermal fibroblasts and promotes their proliferation. G78C can be used as a potential molecular marker for downy Variety.

Diverse partial reprogramming strategies restore youthful gene expression and transiently suppress cell identity

Partial pluripotent reprogramming can reverse features of aging in mammalian cells, but the impact on somatic identity and the necessity of individual reprogramming factors remain unknown. Here, we used single-cell genomics to map the identity trajectory induced by partial reprogramming in multiple murine cell types and dissected the influence of each factor by screening all Yamanaka Factor subsets with pooled single-cell screens. We found that partial reprogramming restored youthful expression in adipogenic and mesenchymal stem cells but also temporarily suppressed somatic identity programs. Our pooled screens revealed that many subsets of the Yamanaka Factors both restore youthful expression and suppress somatic identity, but these effects were not tightly entangled. We also found that a multipotent reprogramming strategy inspired by amphibian regeneration restored youthful expression in myogenic cells. Our results suggest that various sets of reprogramming factors can restore youthful expression with varying degrees of somatic identity suppression. A record of this paper's Transparent Peer Review process is included in the supplemental information.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Inducing Vertebrate Limb Regeneration: A Review of Past Advances and Future Outlook

Limb loss due to traumatic injury or amputation is a major biomedical burden. Many vertebrates exhibit the ability to form and pattern normal limbs during embryogenesis from amorphous clusters of precursor cells, hinting that this process could perhaps be activated later in life to rebuild missing or damaged limbs. Indeed, some animals, such as salamanders, are proficient regenerators of limbs throughout their life span. Thus, research over the last century has sought to stimulate regeneration in species that do not normally regenerate their appendages. Importantly, these efforts are not only a vital aspect of regenerative medicine, but also have fundamental implications for understanding evolution and the cellular control of growth and form throughout the body. Here we review major recent advances in augmenting limb regeneration, summarizing the degree of success that has been achieved to date in frog and mammalian models using genetic, biochemical, and bioelectrical interventions. While the degree of whole limb repair in rodent models has been modest to date, a number of new technologies and approaches comprise an exciting near-term road map for basic and clinical progress in regeneration.

Chemical reprogramming of human somatic cells to pluripotent stem cells

Cellular reprogramming can manipulate the identity of cells to generate the desired cell types^1-3. The use of cell intrinsic components, including oocyte cytoplasm and transcription factors, can enforce somatic cell reprogramming to pluripotent stem cells^4-7. By contrast, chemical stimulation by exposure to small molecules offers an alternative approach that can manipulate cell fate in a simple and highly controllable manner^8-10. However, human somatic cells are refractory to chemical stimulation owing to their stable epigenome^2,11,12 and reduced plasticity^13,14; it is therefore challenging to induce human pluripotent stem cells by chemical reprogramming. Here we demonstrate, by creating an intermediate plastic state, the chemical reprogramming of human somatic cells to human chemically induced pluripotent stem cells that exhibit key features of embryonic stem cells. The whole chemical reprogramming trajectory analysis delineated the induction of the intermediate plastic state at the early stage, during which chemical-induced dedifferentiation occurred, and this process was similar to the dedifferentiation process that occurs in axolotl limb regeneration. Moreover, we identified the JNK pathway as a major barrier to chemical reprogramming, the inhibition of which was indispensable for inducing cell plasticity and a regeneration-like program by suppressing pro-inflammatory pathways. Our chemical approach provides a platform for the generation and application of human pluripotent stem cells in biomedicine. This study lays foundations for developing regenerative therapeutic strategies that use well-defined chemicals to change cell fates in humans.

Tracking of human embryonic stem cell-derived mesenchymal stem cells in premature ovarian failure model mice

Premature ovarian failure (POF) is defined by amenorrhea, hypoestrogenism, elevated gonadotropin levels, and infertility. Chemotherapeutic agents are the most gonadotoxic agents that lead to POF. Although some previous studies have presented that mesenchymal stem cells (MSCs) transplantation could rescue the ovary function of POF animal models through the paracrine pathway, these mechanisms require further investigation. However, mechanisms of embryonic stem cell-derived MSCs (ES-MSCs) therapeutic effects on POF animal models have not been fully investigated yet. This study aimed to evaluate the migration and distribution of ES-MSCs in a model of chemotherapy-induced POF. Female mice received intraperitoneal injections of cyclophosphamide (Cy) to induce POF. Then, MSCs were labeled with green fluorescent protein (GFP) in vitro and injected intravenously into POF mice, and the distribution of MSCs was dynamically monitored at 1 week after transplantation. We harvested the lungs, liver, spleen, ovaries, heart, and kidneys 1 week after transplantation. The sections of these tissues were observed under the fluorescent microscope. More than 70% MSCs were successfully labeled with GFP at 72 h after labeling. MSCs were uniformly distributed in multiple organs and tissues including lungs, liver, spleen, ovaries, heart, and kidneys of POF mice. In mice, at 1week after intravenous transplantation, GFP labeled ES-MSCs were observed in the lungs, liver, spleen, ovaries, heart, and kidneys of POF mice, and the number of GFP labeled ES-MSCs in lungs, ovaries, and heart were higher than that in the spleen, kidneys, and liver. Our results revealed intravenously implanted ES-MSCs could migrate into the various tissues in chemotherapy-induced damaged POF mice.

M2c Macrophages enhance phalange regeneration of amputated mice digits in an organ co-culture system

Objectives

Delayed anti-inflammatory responses and scar-formation are the main causes for inability of injured body parts such as phalanges to regrow in mammals. Salamanders can regenerate fully scar-free body structures, followed by the appearance of anti-inflammatory responses at the injured site immediately after amputation. This study aimed to evaluate the local regenerative effects of direct amplified anti-inflammatory signals on regeneration of amputated mice digit tips using M2c-macrophages in a co-cultured organ system for the first time.

Materials and Methods

We used the amputated digits from the paws of 18.5E day old C57BL/6J mice. Monocytes were obtained from peripheral blood and co-cultured with amputated digits, which subsequently enhanced the M2c macrophage phenotype induced by IL-10. We also examined the regenerative effects of IL-10 and transcription growth factor-beta 1 (TGF-β1).

Results

The regrowth of new tissue occurred 10 days post-amputation in all groups. This regrowth was related to enhanced Msh homeobox-1 (Msx1), Msh homeobox-2 (Msx2), and bone morphogenic protein-4 (Bmp4) genes. Increased expression of fibroblast growth factor-8 (Fgf-8) also increased the proliferation rate. Histological analyses indicated that epidermal-closure occurred at 3-dpa in all groups. We observed full digit tip regeneration in the co-cultured group. Particularly, there was new tissue regrowth observed with 40 µg/ml of IL-10 and 120 µg/ml of TGF-β. In contrast, the control group had no remarkable digit elongation.

Conclusion

We propose that a direct amplified anti-inflammatory response at the digit injury site can regenerate epithelial and mesenchymal tissues, and might be useful for limb regeneration without scar formation in adult mammals.

Activation of adult mammalian retinal stem cells in vivo via antagonism of BMP and sFRP2

Background

The adult mammalian retina does not have the capacity to regenerate cells lost due to damage or disease. Therefore, retinal injuries and blinding diseases result in irreversible vision loss. However, retinal stem cells (RSCs), which participate in retinogenesis during development, persist in a quiescent state in the ciliary epithelium (CE) of the adult mammalian eye. Moreover, RSCs retain the ability to generate all retinal cell types when cultured in vitro, including photoreceptors. Therefore, it may be possible to activate endogenous RSCs to induce retinal neurogenesis in vivo and restore vision in the adult mammalian eye.

Methods

To investigate if endogenous RSCs can be activated, we performed combinatorial intravitreal injections of antagonists to BMP and sFRP2 proteins (two proposed mediators of RSC quiescence in vivo), with or without growth factors FGF and Insulin. We also investigated the effects of chemically-induced N-methyl-N-Nitrosourea (MNU) retinal degeneration on RSC activation, both alone and in combination withthe injected factors. Further, we employed inducible Msx1-Cre^ERT2 genetic lineage labeling of the CE followed by stimulation paradigms to determine if activated endogenous RSCs could migrate into the retina and differentiate into retinal neurons.

Results

We found that in vivo antagonism of BMP and sFRP2 proteins induced CE cells in the RSC niche to proliferate and expanded the RSC population. BMP and sFRP2 antagonism also enhanced CE cell proliferation in response to exogenous growth factor stimulation and MNU-induced retinal degeneration. Furthermore, Msx1-Cre^ERT2 genetic lineage tracing revealed that CE cells migrated into the retina following stimulation and/or injury, where they expressed markers of mature photoreceptors and retinal ganglion cells.

Conclusions

Together, these results indicate that endogenous adult mammalian RSCs may have latent regenerative potential that can be activated by modulating the RSC niche and hold promise as a means for endogenous retinal cell therapy to repair the retina and improve vision.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02630-0.

Control of mesenchymal cell fate via application of FGF-8b in vitro

In order to develop strategies to regenerate complex tissues in mammals, understanding the role of signaling in regeneration competent species and mammalian development is of critical importance. Fibroblast growth factor 8 (FGF-8) signaling has an essential role in limb morphogenesis and blastema outgrowth. Therefore, we aimed to study the effect of FGF-8b on the proliferation and differentiation of mesenchymal stem cells (MSCs), which have tremendous potential for therapeutic use of cell-based therapy. Rat adipose derived stem cells (ADSCs) and muscle progenitor cells (MPCs) were isolated and cultured in growth medium and various types of differentiation medium (osteogenic, chondrogenic, adipogenic, tenogenic, and myogenic medium) with or without FGF-8b supplementation. We found that FGF-8b induced robust proliferation regardless of culture medium. Genes related to limb development were upregulated in ADSCs by FGF-8b supplementation. Moreover, FGF-8b enhanced chondrogenic differentiation and suppressed adipogenic and tenogenic differentiation in ADSCs. Osteogenic differentiation was not affected by FGF-8b supplementation. FGF-8b was found to enhance myofiber formation in rat MPCs. Overall, this study provides foundational knowledge on the effect of FGF-8b in the proliferation and fate determination of MSCs and provides insight in its potential efficacy for musculoskeletal therapies.

Clinicopathological Significances of Cancer Stem Cell-Associated HHEX Expression in Breast Cancer

Aberrant expression of the transcription factor hematopoietic ally expressed homeobox/proline-rich homeodomain (HHEX/PRH) is implicated in numerous cancers. However, the association of HHEX with breast cancer (BC) remains unclear. In this study, HHEX mRNA and protein expression were analyzed using the Oncomine, UALCAN, GEPIA, TCGAportal, and HPA databases. We evaluated the effect of HHEX on clinicopathological parameters using Kaplan–Meier plotter, OncoLnc, TCGAportal, PROGgeneV2, and BC-GenExMiner. Western blotting was performed to compare the level of HHEX in breast samples of Tientsin Albino 2 mice, human breast precancerous lesions, benign breast tumors, and BC. The correlation between HHEX and cancer stem cells was investigated using the GEO (GSE52327 and GSE94865) and GEPIA datasets. Networks between HHEX and survival-related gene marker sets and microRNAs were analyzed using GEPIA, StarBase, and Cytoscape. Results of this study showed that HHEX expression in BC was significantly lower than those in breast precancerous lesions and benign breast tumors at both mRNA and protein levels. BC patients with lower HHEX expression had significantly worse overall survival and disease-free survival. Moreover, HHEX significantly affected the clinicopathology of BC. Specifically, low HHEX expression was correlated with the following groups of patients: age ≤51 years, ER-negative or PR-negative patients, HER-2 positive, triple-negative breast cancer, and basal-like BC. Immunohistochemical analysis of the breast samples showed significant differences of HHEX staining index (P < 0.001) among the three groups. To further investigate the mechanism, we determined the intersection of differentially expressed genes related to BC stem cells and those genes after HHEX expression was altered. This led to the identification of four potentially regulated genes-CXL12, BLNK, PAG1, and LPXN. Using StarBase and km-plotter, the negative regulation of HHEX expression and survival trends, including miR-130b, miR-30e, and miR-301b were joined into miRNA-HHEX-mRNA potential regulatory network. The abilities of proliferation, migration and invasion increased in MDA-MB-231 and BT-549 breast cancer cell lines after HHEX down expression and decreased after HHEX overexpression compared them in the control cells. In conclusion, these data suggest that HHEX expression is downregulated in BC and HHEX may regulate the development of BC through the stem cell-related genes.

Transcriptomic analysis of bone and fibrous tissue morphogenesis during digit tip regeneration in the adult mouse

Humans have limited regenerative potential of musculoskeletal tissues following limb or digit loss. The murine digit has been used to study mammalian regeneration, where stem/progenitor cells (the "blastema") completely regenerate the digit tip after distal, but not proximal, amputation. However, the molecular mechanisms responsible for this response remain to be determined. Here, we evaluated the spatiotemporal formation of bone and fibrous tissues after level-dependent amputation of the murine terminal phalanx and quantified the transcriptome of the repair tissue. Distal (regenerative) and proximal (non-regenerative) amputations showed significant differences in temporal gene expression and tissue regrowth over time. Genes that direct skeletal system development and limb morphogenesis are transiently upregulated during blastema formation and differentiation, including distal Hox genes. Overall, our results suggest that digit tip regeneration is controlled by a gene regulatory network that recapitulates aspects of limb development, and that failure to activate this developmental program results in fibrotic wound healing.

Msx2 plays an important role in BMP6-induced osteogenic differentiation of two mesenchymal cell lines: C3H10T1/2 and C2C12

Bone morphogenetic proteins (BMPs), have been shown to enhance the osteogenic differentiation of mesenchymal cells (MCs) and to promote bone formation. BMP6 is known to play an important role in the process of MCs towards osteogenic differentiation by virtue of their osteoinductive and cell type specific proliferative activity. However, the molecular mechanism relate to BMP6 osteoinductive activity is still unclear and continues to warrant further investigation. Msx2 is a member of the homeobox gene family of transcription factors and promotes calcification. Hence, we wondered if it might also play a role in BMP6-induced osteogenesis. In this study, two mouse mesenchymal cell lines were treated with BMP6, adenovirus-Msx2 (Ad-Msx2) or adenovirus-siMsx2 (Ad-siMsx2). Based on the results of mRNA and protein expression, it was indicated that BMP6 could enhance the expression of Msx2 and activate the phosphorylation of Smad 1/5/8, p38 and ERK1/2. Being transfected by Ad-Msx2, the BMP6-induced activation of phosphorylation was significantly promoted. On the contrary, two cell lines transfected by Ad-siMsx2 presented an inhibited expression of three phosphorylated proteins even after being induced by BMP6. The evaluation of ALP, OPN, OC and calcium deposits revealed the osteogenic results those were corresponding to the results of mRNA and protein. Taken together, these findings can be a novel viewpoint for the understanding of the mechanisms of BMP6-induced osteogenesis and provide therapeutic targets of bone defect.

New insight into functional limb regeneration: A to Z approaches

Limb/digit amputation is a common event in humans caused by trauma, medical illness, or surgery. Although the loss of a digit is not lethal, it affects quality of life and imposes high costs on amputees. In recent years, the increasing interest in limb regeneration has led to enhanced scientific knowledge. However, the limited ability to develop functional limb regeneration in the clinical setting suggests that a challenging issue remains in limb regeneration. Recently, the emergence of regenerative engineering is a promising field to address this challenge and close the gap between science and clinical applications. Cell signalling and molecular mechanisms involved in the limb regeneration process have been extensively studied; however, there is still insufficient data on cell therapy and tissue engineering for limb regeneration. In this review, we intend to focus on therapeutic approaches for limb regeneration that are closely related to gene, immune, and stem cell therapies, as well as tissue engineering approaches that take into consideration the peculiar developmental properties of the limbs. In addition, we attempt to identify the challenges of these strategies for limb regeneration studies in terms of clinical settings and as a road map to accomplish the goal of functional human limb regeneration.

Regenerative Medicine Applications of Mesenchymal Stem Cells

A major research challenge is to develop therapeutics that assist with healing damaged tissues and organs because the human body has limited ability to restore the majority of these tissues and organs to their original state. Tissue engineering (TE) and regenerative medicine (RM) promises to offer efficient therapeutic biological strategies that use mesenchymal stem cells (MSCs). MSCs possess the capability for self-renewal, multilineage differentiation, and immunomodulatory properties that make them attractive for clinical applications. They have been extensively investigated in numerous preclinical and clinical settings in an attempt to overcome their challenges and promote tissue regeneration and repair. This review explores the exciting opportunities afforded by MSCs, their desirable properties as cellular therapeutics in RM, and implicates their potential use in clinical practice. Here, we attempt to identify challenges and issues that determine the clinical efficacy of MSCs as treatment for skeletal and non-skeletal tissues.