Equine Epidermis: A Source of Epithelial-Like Stem/Progenitor Cells with In Vitro and In Vivo Regenerative Capacities

Safety assessment of equine allogeneic tenogenic primed mesenchymal stem cells in horses with naturally occurring tendon and ligament injuries

Background

Mesenchymal stem cells provide a valuable treatment option in orthopedic injuries in horses.

Objectives

The aim of this study was to evaluate the hematological, biochemical, immunological and immunomodulatory parameters following intralesional treatment with tenogenic primed equine allogeneic peripheral blood-derived mesenchymal stem cells (tpMSCs) in client-owned horses with naturally occurring superficial digital flexor tendon (SDFT) and suspensory ligament (SL) injuries.

Methods

The immunogenicity and immunomodulatory capacities of tpMSCs were assessed in a modified mixed lymphocyte reaction, including peripheral blood mononuclear cells (PBMCs) of 14 horses with SDFT and SL injuries after treatment with tpMSCs. In a second study, 18 horses with SDFT and SL injuries received either an intralesional injection with tpMSCs (n = 9) or no treatment (n = 9).

Results

The tpMSCs did not provoke a cellular immune response (p < 0.001) and were able to immunomodulate stimulated T lymphocytes (p < 0.001) in vitro. Therapeutic use of tpMSCs did not result in relevant hematologic or biochemical abnormalities.

Main limitations

Both studies had a small sample size. No statistical analyses were performed in the second study. Fibrinogen was only analyzed in a single horse prior to treatment.

Conclusion

Co-incubation of tpMSCs and PBMCs of horses that have been previously exposed to tpMSCs did not elicit a cellular immune response and tpMSCs were able to immunomodulate stimulated T lymphocytes. Intralesional treatment with tpMSCs did not provoke abnormal changes in hematological and biochemical parameters.

Use of Biologics and Stem Cells for Wound Healing in the Horse

Treatment of skin wounds is a high priority in veterinary medicine because healthy uncompromised skin is essential for the well-being of horses. Stem cells and other biologic therapies offer benefits by reducing the need for surgical procedures and conventional antibiotics. Evidence from in vitro studies and small in vivo trials supports the use of equine stem cells and biologics for the treatment of acute and chronic cutaneous wounds. Larger clinical trials are warranted to better evaluate the regenerative and immunological responses to these treatments. Additionally, delivery methods and treatment schedules should be optimized to improve efficacy of these novel therapies.

Cellular and Humoral Immunogenicity Investigation of Single and Repeated Allogeneic Tenogenic Primed Mesenchymal Stem Cell Treatments in Horses Suffering From Tendon Injuries

The use of mesenchymal stem cells (MSCs) for the treatment of equine tendon disease is widely investigated because of their regenerative and immunomodulatory potential. However, questions have been raised concerning the immunogenic properties of allogeneic MSCs. Therefore, two studies were conducted to assess the safety of equine allogeneic peripheral blood-derived tenogenic primed MSCs (tpMSCs). The objective was to evaluate if a single and repeated tpMSC administration induced a cellular and humoral immune response in horses suffering from tendon injuries. Horses enrolled in the first study (n = 8) had a surgically induced superficial digital flexor tendon core lesion and were treated intralesionally with tpMSCs. Before and after treatment the cellular immunogenicity was assessed by modified mixed lymphocyte reactions. The humoral immune response was investigated using a crossmatch assay. Presence of anti-bovine serum albumin (BSA) antibodies was detected via ELISA. Horses enrolled in the second study (n = 6) suffered from a naturally occurring tendon injury and were treated twice with tpMSCs. Blood was collected after the second treatment for the same immunological assays. No cellular immune response was found in any of the horses. One out of eight horses in the first study and none of the horses in the second study had anti-tpMSC antibodies. This particular horse had an equine sarcoid and further investigation revealed presence of antibodies against sarcoid cells and epithelial-like stem cells before treatment, which increased after treatment. Additionally, formation of antibodies against BSA was observed. These findings might indicate a non-specific immune response generated after treatment. Serum from the other horses revealed no such antibody formation. These two studies showed that the administration of tpMSCs did not induce a cellular or humoral immune response following an intralesional single or repeated (two consecutive) allogeneic tpMSC treatment in horses with tendon injury, except for one horse. Therefore, a larger field study should confirm these findings and support the safe use of tpMSCs as a therapeutic for horses suffering from tendon injuries.

Approaches for Regenerative Healing of Cutaneous Wound with an Emphasis on Strategies Activating the Wnt/β-Catenin Pathway

Significance: In adult mammals, spontaneous repair of a cutaneous wound occurs slowly and leaves a scar with skin adnexa deficiencies. To accelerate cutaneous wound-healing rates and avoid scar formation, current studies have focused on regenerative therapies. Recent Advances: Emerging therapeutics for regenerative wound healing often focus on the use of growth factors and stem cells. However, these therapeutic approaches have limited routine clinical use due to high costs and technical requirements. Critical Issue: Understanding the molecular mechanisms involved in the signaling pathways for cutaneous wound healing and neogenic synthesis of the skin components is important for identification of novel targets for the development of regenerative wound-healing agents. Future Directions: The Wnt/β-catenin pathway is a well-known key player for enhancement of the overall healing process involving tissue regeneration via crosstalk with other signaling pathways. Strategies that activate the Wnt/β-catenin pathway via modulation of the pathway-controlling regulatory factors could provide effective therapeutic approaches for regenerative wound healing.

The Equine Hoof: Laminitis, Progenitor (Stem) Cells, and Therapy Development

The equine hoof capsule, composed of modified epidermis and dermis, is vital for protecting the third phalanx from forces of locomotion. There are descriptions of laminitis, defined as inflammation of sensitive hoof tissues but recognized as pathologic changes with or without inflammatory mediators, in the earliest records of domesticated horses. Laminitis can range from mild to serious, and signs can be acute, chronic, or transition from acute, severe inflammation to permanently abnormal tissue. Damage within the intricate dermal and epidermal connections of the primary and secondary lamellae is often associated with lifelong changes in hoof growth, repair, and conformation. Decades of research contribute to contemporary standards of care that include systemic and local therapies as well as mechanical hoof support. Despite this, consistent mechanisms to restore healthy tissue formation following a laminitic insult are lacking. Endogenous and exogenous progenitor cell contributions to healthy tissue formation is established for most tissues. There is comparably little information about equine hoof progenitor cells. Equine hoof anatomy, laminitis, and progenitor cells are covered in this review. The potential of progenitor cells to advance in vitro equine hoof tissue models and translate to clinical therapies may significantly improve prevention and treatment of a devastating condition that has afflicted equine companions throughout history.

Knockdown of Tcf3 enhances the wound healing effect of bone marrow mesenchymal stem cells in rats

The aim of the present study was to explore the wound healing effect of Tcf3 in rat bone marrow mesenchymal stem cells (BMSCs) and their effects on wound healing. Epidermal growth factor (EGF) and fibroblast growth factors (FGFs) were used to induce BMSCs differentiation into epithelial-like cells. Western Blotting analysis and RT-qPCR were performed to assess the expression levels of Tcf3 and the markers of epithelial-like cells, such as Cytokeratin-18 (CK-18), CK-19 and P63. Cell counting kit-8 (CCK-8) and clone formation assay were carried out to detect cell viability. Immunohistochemistry and HE staining were used to assess the level of Tcf3 protein and skin repair degree, respectively. Rat wound healing model was built to evaluate the effects of BMSCs with altered expression of Tcf3 on wound healing. Results showed that EGF and FGFs stimulation increased the expression of CK-18, CK-19 and P63, improved BMSCs viability, but decreased the expression of Tcf3. Knockdown of Tcf3 in BMSCs increased CK-18, CK-19 and P63 expression and improved cell proliferation, as well as accelerated wound healing process. Moreover, inhibition of Wnt/β-catenin signaling weakened the effect of Tcf3 down-regulation on BMSCs proliferation enhancement. And inhibition of Notch1 signaling impeded the epithelial-like cell differentiation of BMSCs induced by Tcf3 down-regulation. Our study reveals that knockdown of Tcf3 enhances the wound healing process of BMSCs in rat, which provides new approach for accelerating skin regeneration.

Ultrastructural morphology is distinct among primary progenitor cell isolates from normal, inflamed, and cryopreserved equine hoof tissue and CD105+K14+ progenitor cells

The equine hoof dermal-epidermal interface requires progenitor cells with distinct characteristics. This study was designed to provide accurate ultrastructural depictions of progenitor cells isolated from inflamed tissue and normal tissue before and after cryopreservation and following selection of cells expressing both keratin (K) 14 (ectodermal) and cluster of differentiation (CD) 105 (mesodermal). Passage 3 cell ultrastructure was assessed following 2D culture and after 3D culture on decellularized hoof tissue scaffolds. Outcome measures included light, transmission electron, and scanning electron microscopy, immunocytochemistry, and CD105⁺K14⁺ cell trilineage plasticity. Cells from normal tissue had typical progenitor cell characteristics. Those from inflamed tissue had organelles and morphology consistent with catabolic activities including lysosomes, irregular rough endoplasmic reticulum, and fewer vacuoles and early endosomes than those from normal tissue. Cryopreserved tissue cells appeared apoptotic with an irregular cell membrane covered by cytoplasmic protrusions closely associated with endocytic and exocytic vesicles, chromatin aggregated on the nuclear envelop, abundant, poorly organized rough endoplasmic reticulum, and plentiful lysosomes. Cells that were CD105⁺K14⁺ were distinguishable from heterogenous cells by infrequent microvilli on the cell surface, sparse endosomes and vesicles, and desmosomes between cells. Cells expressed ectodermal (K15) and mesodermal (CD105) proteins in 2D and 3D cultures. Inflamed and cryopreserved tissue isolates attached poorly to tissue scaffold while normal tissue cells attached well, but only CD105⁺K14⁺ cells produced extracellular matrix after 4 d. The CD105⁺K14⁺ cells exhibited osteoblastic, adipocytic, and neurocytic differentiation. Ultrastructural information provided by this study contributes to understanding of equine hoof progenitor cells to predict their potential contributions to tissue maintenance, healing, and damage as well post-implantation behavior.

In vitro Characteristics of Heterogeneous Equine Hoof Progenitor Cell Isolates

Damage to an ectodermal-mesodermal interface like that in the equine hoof and human finger nail bed can permanently alter tissue structure and associated function. The purpose of this study was to establish and validate in vitro culture of primary progenitor cell isolates from the ectodermal-mesodermal tissue junction in equine hooves, the stratum internum, with and without chronic inflammation known to contribute to lifelong tissue defects. The following were evaluated in hoof stratum internum cell isolates up to 5 cell passages (P): expansion capacity by cell doublings and doubling time; plasticity with multi-lineage differentiation and colony-forming unit (CFU) frequency percentage; immunophenotype with immunocytochemistry and flow cytometry; gene expression with RT-PCR; and ultrastructure with transmission electron microscopy. The presence of keratin (K)14, 15 and K19 as well as cluster of differentiation (CD)44 and CD29 was determined in situ with immunohistochemistry. To confirm in vivo extracellular matrix (ECM) formation, cell-scaffold (polyethylene glycol/poly-L-lactic acid and tricalcium phosphate/hydroxyapatite) constructs were evaluated with scanning electron microscopy 9 weeks after implantation in athymic mice. Cultured cells had characteristic progenitor cell morphology, expansion, CFU frequency percentage and adipocytic, osteoblastic, and neurocytic differentiation capacity. CD44, CD29, K14, K15 and K19 proteins were present in native hoof stratum internum. Cultured cells also expressed K15, K19 and desmogleins 1 and 3. Gene expression of CD105, CD44, K14, K15, sex determining region Y-box 2 (SOX2) and octamer-binding transcription factor 4 (OCT4) was confirmed in vitro. Cultured cells had large, eccentric nuclei, elongated mitochondria, and intracellular vacuoles. Scaffold implants with cells contained fibrous ECM 9 weeks after implantation compared to little or none on acellular scaffolds. In vitro expansion and plasticity and in vivo ECM deposition of heterogeneous, immature cell isolates from the ectodermal-mesodermal tissue interface of normal and chronically inflamed hooves are typical of primary cell isolates from other adult tissues, and they appear to have both mesodermal and ectodermal qualities in vitro. These results establish a unique cell culture model to target preventative and restorative therapies for ectodermal-mesodermal tissue junctions.

Biobanking Organoids or Ground-State Stem Cells?

Autologous transplantation of human epidermal stem cells cultured in Green's method is one of the first examples of utilizing adult stem cells in regenerative medicine. Using the same method, we cloned p63-expressing distal airway stem cells and showed their essential role in lung regeneration in a mouse model of acute respiratory distress syndrome. However, adult stem cells of columnar epithelial tissues had until recently evaded all attempts at cloning. To address this issue, we developed a novel technology that enabled cloning ground-state stem cells of the columnar epithelium. The adaption of this technology to clone stem cells of cancer precursors furthered our understanding of the dynamics of processes such as clonal evolution and dominance in Barrett's esophagus, as well as for testing platforms for chemical screening. Taken together, the properties of these ground-state stem cells, including unlimited propagation, genomic stability, and regio-specificity, make them ideal for regenerative medicine, disease modeling and drug discovery.

Normal microscopic anatomy of equine body and limb skin: A morphological and immunohistochemical study

INTRODUCTION

Information on microscopic anatomy of equine skin is sparse. In horses, limb wounds often become chronic and/or non-healing whereas body wounds heal normally. These dissimilarities in healing patterns might be a product of different phenotypic characteristics of body and limb skin. The objective of this study was to investigate microscopic anatomy, epidermal thickness, keratinocyte proliferation and differentiation as well as the presence of mast cells in normal equine skin of body and limb.

MATERIALS AND METHODS

The study involved body and limb skin biopsies from six horses. Histological characteristics of the epidermis were assessed and epithelial thickness measured. Immunohistochemistry was performed to investigate epidermal differentiation patterns of cytokeratin (CK) 10, CK14, CK16, loricrin, and peroxisome proliferator-activated receptor alpha (PPAR-α), epidermal proliferation (Ki-67 immunostaining), and mast cells distribution in the skin.

RESULTS

The epidermis was significantly thicker in the limb skin compared to body skin (p<0.01). Epidermal proliferation and CK distribution did not show differences in the two anatomical areas. Loricrin presence was focally found in the spinous layer in four out of six limb skin samples but not in body skin samples. Tryptase positive mast cells were detected in the dermis and their density (cell/mm²) was not different between body and limb.

DISCUSSION AND CONCLUSION

Here we report for the first time about the normal distribution of CK10, CK14, CK16, PPAR-α, and loricrin in equine limb and body skin as well as about epidermal proliferation rate and mast cell count. It will be relevant to investigate the distribution of the investigated epithelial differentiation markers and the role of mast cells during equine wound healing and/or other skin diseases.

Allogeneic Stem Cells Alter Gene Expression and Improve Healing of Distal Limb Wounds in Horses

Distal extremity wounds are a significant clinical problem in horses and humans and may benefit from mesenchymal stem cell (MSC) therapy. This study evaluated the effects of direct wound treatment with allogeneic stem cells, in terms of gross, histologic, and transcriptional features of healing. Three full-thickness cutaneous wounds were created on each distal forelimb in six healthy horses, for a total of six wounds per horse. Umbilical cord-blood derived equine MSCs were applied to each wound 1 day after wound creation, in one of four forms: (a) normoxic- or (b) hypoxic-preconditioned cells injected into wound margins, or (c) normoxic- or (d) hypoxic-preconditioned cells embedded in an autologous fibrin gel and applied topically to the wound bed. Controls were one blank (saline) injected wound and one blank fibrin gel-treated wound per horse. Data were collected weekly for 6 weeks and included wound surface area, thermography, gene expression, and histologic scoring. Results indicated that MSC treatment by either delivery method was safe and improved histologic outcomes and wound area. Hypoxic-preconditioning did not offer an advantage. MSC treatment by injection resulted in statistically significant increases in transforming growth factor beta and cyclooxygenase-2 expression at week 1. Histologically, significantly more MSC-treated wounds were categorized as pro-healing than pro-inflammatory. Wound area was significantly affected by treatment: MSC-injected wounds were consistently smaller than gel-treated or control wounds. In conclusion, MSC therapy shows promise for distal extremity wounds in horses, particularly when applied by direct injection into the wound margin. Stem Cells Translational Medicine 2018;7:98-108.

Wound-healing markers after autologous and allogeneic epithelial-like stem cell treatment

BACKGROUND AIMS

Several cytokines and growth factors play an essential role in skin regeneration and epithelial-like stem cells (EpSCs) have beneficial effects on wound healing in horses. However, there are no reports available on the expression of these growth factors and cytokines after EpSC therapy.

METHODS

Wounds of 6 cm(2) were induced in the gluteus region of 6 horses and treated with (i) autologous EpSCs, (ii) allogeneic EpSCs, (iii) vehicle treatment or (iv) untreated control. Real time polymerase chain reaction was performed on tissue biopsies taken 1 and 5 weeks after these treatments to evaluate mRNA expression of interferon (IFN)-γ, interleukin (IL)-6, vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), insulin-like growth factor (IGF)-1 and epidermal keratin (eKER).

RESULTS

One week after treatments, mRNA levels of IL-6 (P = 0.012) and VEGF (P = 0.008) were higher in allogeneic EpSC-treated wounds compared with controls. Also, mRNA levels of IGF-1 were higher at 1 week in both autologous (P = 0.027) and allogeneic (P = 0.035) EpSC-treated wounds. At week 5, all EpSC- and vehicle-treated wounds demonstrated significantly higher IFN-γ, VEGF and eKER mRNA expression compared with controls and compared with their respective levels at week 1.

CONCLUSIONS

Equine wounds treated with allogeneic EpSCs demonstrate a significant increase in mRNA expression of IL-6, VEGF and IGF-1 in the acute phase. In the longer term, an increase in IFN-γ, VEGF and eKER mRNA was detected in the wounds treated with allogenic EpSCs, autologous EpSCs or their vehicle.

Comparison of autologous versus allogeneic epithelial-like stem cell treatment in an in vivo equine skin wound model

BACKGROUND AIMS

Several studies report beneficial effects of autologous and allogeneic stem cells on wound healing. However, no comparison between autologous versus allogeneic epithelial-like stem cells (EpSCs) has been made so far. For this reason, we first hypothesize that both EpSC types enhance wound healing in comparison to vehicle treatment and untreated controls. Second, on the basis of other studies, we hypothesized that there would be no difference between autologous and allogeneic EpSCs.

METHODS

Twelve full-thickness skin wounds were created in six horses. Each horse was subjected to (i) autologous EpSCs, (ii) allogeneic EpSCs, (iii) vehicle treatment or (iv) untreated control. Wound evaluation was performed at day 3, 7 and 14 through wound exudates and at week 1, 2 and 5 through biopsies.

RESULTS

Wound circumference and surface were significantly smaller in autologous EpSC-treated wounds. A significantly lower amount of total granulation tissue (overall) and higher vascularization (week 1) was observed after both EpSC treatments. Significantly more major histocompatibility complex II-positive and CD20-positive cells were noticed in EpSC-treated wounds at week 2. In autologous and allogeneic groups, the number of EpSCs in center biopsies was low after 1 week (11.7% and 6.1%), decreased to 7.6% and 1.7%, respectively (week 2), and became undetectable at week 5.

CONCLUSIONS

These results confirm the first hypothesis and partially support the second hypothesis. Besides macroscopic improvements, both autologous and allogeneic EpSCs had similar effects on granulation tissue formation, vascularization and early cellular immune response.

Differentiation of equine induced pluripotent stem cells into a keratinocyte lineage

REASONS FOR PERFORMING STUDY

Skin trauma in horses often leads to the development of chronic nonhealing wounds that lack a keratinocyte cover, vital for healing. Reports in mouse and man confirm the possibility of generating functional keratinocytes from induced pluripotent stem cells (iPSC), thus presenting myriad potential applications for wound management or treatment of skin disease. Similarly, differentiation of equine iPSC (eiPSC) into a keratinocyte lineage should provide opportunities for the advancement of veterinary regenerative medicine.

OBJECTIVES

The purpose of this study was to develop an efficient method for the differentiation of eiPSC into a keratinocyte lineage. It was hypothesised that eiPSC can form differentiated keratinocytes (eiPSC-KC) comparable with primary equine keratinocytes (PEK) in their morphological and functional characteristics.

STUDY DESIGN

Experimental in vitro study.

METHODS

Equine iPSC established using a nonviral system were treated for 30 days with retinoic acid and bone morphogenetic protein-4 to induce directed differentiation into iPSC-KC. Temporospatial gene and protein expression by eiPSC-KC was measured at weekly intervals of differentiation and in response to calcium switch. Proliferative and migratory capacities of eiPSC-KC were compared with those of PEK.

RESULTS

Equine iPSC, upon directed differentiation, showed loss of pluripotency genes and progressive increase in pancytokeratin expression indicating ectodermal specification into keratinocytes. High differentiation efficiency was achieved, with 82.5% of eiPSC expressing keratin 14, a marker of epidermal-specific basal stem cells, after 30 days of directed differentiation. Moreover, the proliferative capacity of eiPSC-KC was superior, while the migratory capacity (measured as the ability to epithelise in vitro wounds) was comparable with that of PEK.

CONCLUSIONS

This proof of concept study suggests that eiPSC can successfully be differentiated into equine keratinocytes (eiPSC-KC) with features that are promising to the development of a stem cell-based skin construct, with the potential to regenerate lost or damaged skin.

Expression and localization of epithelial stem cell and differentiation markers in equine skin, eye and hoof

BACKGROUND

The limited characterization of equine skin, eye and hoof epithelial stem cell (ESC) and differentiation markers impedes the investigation of the physiology and pathophysiology of these tissues.

HYPOTHESIS/OBJECTIVES

To characterize ESC and differentiation marker expression in epithelial tissues of the equine eye, haired skin and hoof capsule.

METHODS

Indirect immunofluorescence microscopy and immunoblotting were used to detect expression and tissue localization of keratin (K) isoforms K3, K10, K14 and K124, the transcription factor p63 (a marker of ESCs) and phosphorylated p63 [pp63; a marker of ESC transition to transit-amplifying (TA) cell] in epithelial tissues of the foot (haired skin, hoof coronet and hoof lamellae) and the eye (limbus and cornea).

RESULTS

Expression of K14 was restricted to the basal layer of epidermal lamellae and to basal and adjacent suprabasal layers of the haired skin, coronet and corneal limbus. Coronary and lamellar epidermis was negative for both K3 and K10, which were expressed in the cornea/limbus epithelium and haired skin epidermis, respectively. Variable expression of p63 with relatively low to high levels of phosphorylation was detected in individual basal and suprabasal cells of all epithelial tissues examined.

CONCLUSIONS

To the best of the author's knowledge, this is the first report of the characterization of tissue-specific keratin marker expression and the localization of putative epithelial progenitor cell populations, including ESCs (high p63 expression with low pp63 levels) and TA cells (high expression of both p63 and pp63), in the horse. These results will aid further investigation of epidermal and corneal epithelial biology and regenerative therapies in horses.

Mesenchymal Stem Cell Therapy Alleviates Interstitial Cystitis by Activating Wnt Signaling Pathway

Interstitial cystitis (IC) is a syndrome characterized by urinary urgency, frequency, pelvic pain, and nocturia in the absence of bacterial infection or identifiable pathology. IC is a devastating disease that certainly decreases quality of life. However, the causes of IC remain unknown and no effective treatments or cures have been developed. This study evaluated the therapeutic potency of using human umbilical cord-blood-derived mesenchymal stem cells (UCB-MSCs) to treat IC in a rat model and to investigate its responsible molecular mechanism. IC was induced in 10-week-old female Sprague-Dawley rats via the instillation of 0.1 M HCl or phosphate-buffered saline (PBS; sham). After 1 week, human UCB-MSC (IC+MSC) or PBS (IC) was directly injected into the submucosal layer of the bladder. A single injection of human UCB-MSCs significantly attenuated the irregular and decreased voiding interval in the IC group. Accordingly, denudation of the epithelium and increased inflammatory responses, mast cell infiltration, neurofilament production, and angiogenesis observed in the IC bladders were prevented in the IC+MSC group. The injected UCB-MSCs successfully engrafted to the stromal and epithelial tissues and activated Wnt signaling cascade. Interference with Wnt and epidermal growth factor receptor activity by small molecules abrogated the benefits of MSC therapy. This is the first report that provides an experimental evidence of the therapeutic effects and molecular mechanisms of MSC therapy to IC using an orthodox rat animal model. Our findings not only provide the basis for clinical trials of MSC therapy to IC but also advance our understanding of IC pathophysiology.