PKH26 is an excellent retrograde and anterograde fluorescent tracer characterized by a small injection site and strong fluorescence emission

Slow-replicating leukemia cells represent a leukemia stem cell population with high cell-surface CD74 expression

Persistence of quiescent leukemia stem cells (LSCs) after treatment most likely contributes to chemotherapy resistance and poor prognosis of leukemia patients. Identification of this quiescent cell population would facilitate eradicating LSCs. Here, using a cell-tracing PKH26 (PKH) dye that can be equally distributed to daughter cells following cell division in vivo, we identify a label-retaining slow-cycling leukemia cell population from AML1-ETO9a (AE9a) leukemic mice. We find that, compared with cells not maintaining PKH-staining, a higher proportion of PKH-retaining cells are in G0 phase, and PKH-retaining cells exhibit increased colony formation ability and leukemia initiation potential. In addition, PKH-retaining cells possess high chemo-resistance and are more likely to be localized to the endosteal bone marrow region. Based on the transcriptional signature, HLA class II histocompatibility antigen gamma chain (Cd74) is highly expressed in PKH-retaining leukemia cells. Furthermore, cell surface CD74 was identified to be highly expressed in LSCs of AE9a mice and CD34+ human leukemia cells. Compared to Lin-CD74- leukemia cells, Lin-CD74+ leukemia cells of AE9a mice exhibit higher stemness properties. Collectively, our findings reveal that the identified slow-cycling leukemia cell population represents an LSC population, and CD74+ leukemia cells possess stemness properties, suggesting that CD74 is a candidate LSC surface marker.

Every road leads to Rome: therapeutic effect and mechanism of the extracellular vesicles of human embryonic stem cell-derived immune and matrix regulatory cells administered to mouse models of pulmonary fibrosis through different routes

Background

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal interstitial lung disease. Whether extracellular vesicles are effective in treating IPF and what is the optimal administrative route is not clear. Our previous studies have shown that immunity and matrix regulatory cells (IMRCs) derived from human embryonic stem cells can safely treat lung injury and fibrosis in mouse models, and its mechanism of action is related to the paracrine effect. In this study, we investigated the therapeutic effects of IMRC-derived extracellular vesicles (IMRC-EVs) on a bleomycin-induced pulmonary fibrosis mouse model and explored the optimal route of administration.

Methods

To study the biodistribution of IMRC-EVs after administration via different routes, NIR labeled-IMRC-EVs were delivered by intratracheal (IT) or intravenous (IV) route, and in vivo imaging was acquired at different time points. The therapeutic effects of IMRC-EVs delivered by different routes were analyzed by assessing histology, lung function, cytokines levels, and transcriptome profiling. RNA-seq of lung tissues was performed to investigate the mechanisms of EV treatment through IT or IV administrations.

Results

IMRC-EVs mainly reserved in the liver and spleen when administrated via IV route; and mainly retained in the lungs via the IT route. IMRC-EVs administrated via both routes demonstrated a therapeutic effect as attenuated pulmonary fibrosis, improved lung function, and histological parameters. Based on our RNA-seq results, different pathways may be affected by IMRC-EVs administrated via IT or IV routes. In addition, in vitro experiments showed that IMRC-EVs inhibited epithelial-to-mesenchymal transition induced by TGF-β.

Conclusion

IMRC-EVs administrated via IT or IV routes generate different biodistributions, but are both effective for the treatment of bleomycin-induced pulmonary fibrosis. The therapeutic mechanisms of IMRC-EVs administrated via different routes may be different.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02839-7.

Human embryonic mesenchymal stem cells participate in differentiation of renal tubular cells in newborn mice

Stem cells are used with increasing success in the treatment of renal tubular injury. However, whether mesenchymal stem cells (MSC) differentiate into renal tubular epithelial cells remains controversial. The aims of the present study were to observe the localization of human embryonic MSCs (hMSCs) in the kidneys of newborn mice, and to investigate hMSC differentiation into tubular epithelium. Primary culture hMSCs were derived from 4–7-week-old embryos and labeled with the cell membrane fluorescent dye PKH-26. The degree of apoptosis, cell growth, differentiation and localization of hMSCs with and without this label were then determined using immunohistochemical methods and flow cytometry. hMSCs and PKH26-labeled hMSCs were revealed to differentiate into chondrocytes and adipocytes, and were demonstrated to have similar proliferative capability. In the two cell types, the antigens CD34 and CD45, indicative of hematopoietic lineages, were not expressed; however, the expression of the mesenchymal markers CD29 and CD90 in MSCs, was significantly increased. During a 4-week culture period, laser confocal microscopy revealed that PKH26-labeled hMSCs in the kidneys of newborn mice gradually dispersed. Two weeks after the injection of the PKH26-labeled cells, the percentage of PKH26-labeled hMSCs localized to the renal tubules was 10±2.1%. In conclusion, PKH26 labeling has no effect on hMSC differentiation, proliferation and mesenchymal cell surface features, and hMSCs injected into the kidneys of newborn mice may transform to renal tubule epithelium.

The Effect of Mesenchymal Stem Cells and Chitosan Gel on Full Thickness Skin Wound Healing in Albino Rats: Histological, Immunohistochemical and Fluorescent Study

Background

Wound healing involves the integration of complex biological processes. Several studies examined numerous approaches to enhance wound healing and to minimize its related morbidity. Both chitosan and mesenchymal stem cells (MSCs) were used in treating skin wounds. The aim of the current work was to compare MSCs versus chitosan in wound healing, evaluate the most efficient route of administration of MSCs, either intradermal or systemic injection, and elicit the mechanisms inducing epidermal and dermal cell regeneration using histological, immunohistochemical and fluorescent techniques.

Material and Methods

Forty adult male Sprague Dawley albino rats were divided into four equal groups (ten rats in each group): control group (Group I); full thickness surgical skin wound model, Group II: Wound and chitosan gel. Group III: Wound treated with systemic injection of MSCs and Group IV: Wound treated with intradermal injection of MSCs. The healing ulcer was examined on day 3, 5, 10 and 15 for gross morphological evaluation and on day 10 and 15 for histological, immunohistochemical and fluorescent studies.

Results

Chitosan was proved to promote wound healing more than the control group but none of their wound reached complete closure. Better and faster healing of wounds in MSCs treated groups were manifested more than the control or chitosan treated groups. It was found that the intradermal route of administration of stem cells enhanced the rate of healing of skin wounds better than the systemic administration to the extent that, by the end of the fifteenth day of the experiment, the wounds were completely healed in all rats of this group. Histologically, the wound areas of group IV were hardly demarcated from the adjacent normal skin and showed complete regeneration of the epidermis, dermis, hypodermis and underlying muscle fibers. Collagen fibers were arranged in many directions, with significant increase in their area percent, surrounding fully regenerated hair follicles and sebaceous glands in the dermis of the healed areas more than in other groups.

Conclusion

MSCs enhanced the healing process of wound closure more than chitosan gel treatment. Furthermore, MSCs injected intradermally, were more efficient in accelerating wound healing than any other mode of treatment.

Effect of bone marrow derived mesenchymal stem cells on healing of induced full-thickness skin wounds in albino rat

BACKGROUND AND OBJECTIVES

Mesenchymal stem cells have delivered new approaches to the management of wound healing in severe skin injuries. This work was planned to evaluate the effect of bone marrow-derived mesenchymal stem cells (BMSCs) on healing of induced full thickness skin wounds in albino rats using topical & systemic injections.

METHODS AND RESULTS

Forty adult male albino rats were classified into 2 groups after induction of full thickness skin wound; untreated group and stem cell-treated group. The latter was further subdivided into topically and systemically treated ones. BMSCs were isolated & labeled by PKH26 before injection. Healing of wounds was evaluated grossly. Skin biopsies were obtained one & three weeks after wound induction. Sections were stained with Hematoxylin & Eosin, Masson's trichrome and immunohistochemichal stain for vascular endothelial growth factor (VEGF). Epidermal thicknesses and mean area percent of both collagen fibers & VEGF immunopositive cells were measured using image analyzer & results were subjected to statistical analysis. PKH26 fluorescent-labeled cells were found in the regenerated epidermis, hair follicles and dermis in BMSCs-treated groups. By the end of the third week, the wounds of BMSCs-treated groups showed full regeneration of epidermis, re-organization of collagen and decrease in VEGF immunopositive cells. Delayed wound healing was seen in 20% of systemically treated rats. Significant increase in the mean area percent of collagen fibers was detected in topically treated group.

CONCLUSIONS

Both methods of BMSCs injection were effective in healing of full thickness skin wound but topical method was more effective.

PKH26 can transfer to host cells in vitro and vivo

The fluorescent dye, PKH26, which mainly binds to the cell membrane, has been used as the cell tracer to locate the transplanted cells in host for a long time. However, there was no detailed report that whether the PKH26 dye was specific to the transplanted cells. Therefore, the aim of this article is to explore the effect of cells debris as the cracking cells from the PKH26-labeled adipose-derived stem cells (ADSCs) on the cells in vitro and the host in vivo. After we tested the proliferation and toxicity of PKH26 to the ADSCs by the Cell Count-8 kit and alamar blue assay, we constructed 2 models, coculturing lots of PKH26-labeled cell debris with the unlabeled ADSCs in vitro and injecting via the tail vein in rat, to evaluate the specificity of the PKH26 dye. The result indicated that the PKH26 didn't inhibit the proliferation and had no toxicity to the ADSCs compared with the unlabeled ADSCs, but the cell debris cracking from PKH26-labeled transplanted cells can cause the unlabeled cells to emit red fluorescence in vitro and also lead the tissues displaying red fluorescence in vivo. We can conclude that the PKH26 dye, used as a cell tracer for a long time, was not an ideal cell tracer.