Skin mesenchymal niches maintain and protect AML-initiating stem cells.

Leukemia cutis or leukemic cell infiltration in skin is one of the common extramedullary manifestations of acute myeloid leukemia (AML) and signifies a poorer prognosis. However, its pathogenesis and maintenance remain understudied. Here, we report massive AML cell infiltration in the skin in a transplantation-induced MLL-AF9 AML mouse model. These AML cells could regenerate AML after transplantation. Prospective niche characterization revealed that skin harbored mesenchymal progenitor cells (MPCs) with a similar phenotype as BM mesenchymal stem cells. These skin MPCs protected AML-initiating stem cells (LSCs) from chemotherapy in vitro partially via mitochondrial transfer. Furthermore, Lama4 deletion in skin MPCs promoted AML LSC proliferation and chemoresistance. Importantly, more chemoresistant AML LSCs appeared to be retained in Lama4-/- mouse skin after cytarabine treatment. Our study reveals the characteristics and previously unrecognized roles of skin mesenchymal niches in maintaining and protecting AML LSCs during chemotherapy, meriting future exploration of their impact on AML relapse.

Characterization of the bone marrow niche in patients with chronic myeloid leukemia identifies CXCL14 as a new therapeutic option.

Although tyrosine kinase inhibitors (TKIs) are effective in treating chronic myeloid leukemia (CML), they often fail to eradicate the leukemia-initiating stem cells (LSCs), causing disease persistence and relapse. Evidence indicates that LSC persistence may be because of bone marrow (BM) niche protection; however, little is known about the underlying mechanisms. Herein, we molecularly and functionally characterize BM niches in patients with CML at diagnosis and reveal the altered niche composition and function in these patients. Long-term culture initiating cell assay showed that the mesenchymal stem cells from patients with CML displayed an enhanced supporting capacity for normal and CML BM CD34+CD38- cells. Molecularly, RNA sequencing detected dysregulated cytokine and growth factor expression in the BM cellular niches of patients with CML. Among them, CXCL14 was lost in the BM cellular niches in contrast to its expression in healthy BM. Restoring CXCL14 significantly inhibited CML LSC maintenance and enhanced their response to imatinib in vitro, and CML engraftment in vivo in NSG-SGM3 mice. Importantly, CXCL14 treatment dramatically inhibited CML engraftment in patient-derived xenografted NSG-SGM3 mice, even to a greater degree than imatinib, and this inhibition persisted in patients with suboptimal TKI response. Mechanistically, CXCL14 upregulated inflammatory cytokine signaling but downregulated mTOR signaling and oxidative phosphorylation in CML LSCs. Together, we have discovered a suppressive role of CXCL14 in CML LSC growth. CXCL14 might offer a treatment option targeting CML LSCs.

Critical role of Lama4 for hematopoiesis regeneration and acute myeloid leukemia progression.

Impairment of normal hematopoiesis and leukemia progression are 2 well-linked processes during leukemia development and are controlled by the bone marrow (BM) niche. Extracellular matrix proteins, including laminin, are important BM niche components. However, their role in hematopoiesis regeneration and leukemia is unknown. Laminin α4 (Lama4), a major receptor-binding chain of several laminins, is altered in BM niches in mice with acute myeloid leukemia (AML). So far, the impact of Lama4 on leukemia progression remains unknown. We here report that Lama4 deletion in mice resulted in impaired hematopoiesis regeneration following irradiation-induced stress, which is accompanied by altered BM niche composition and inflammation. Importantly, in a transplantation-induced MLL-AF9 AML mouse model, we demonstrate accelerated AML progression and relapse in Lama4-/- mice. Upon AML exposure, Lama4-/- mesenchymal stem cells (MSCs) exhibited dramatic molecular alterations, including upregulation of inflammatory cytokines that favor AML growth. Lama4-/- MSCs displayed increased antioxidant activities and promoted AML stem cell proliferation and chemoresistance to cytarabine, which was accompanied by increased mitochondrial transfer from the MSCs to AML cells and reduced reactive oxygen species in AML cells in vitro. Similarly, we detected lower levels of reactive oxygen species in AML cells from Lama4-/- mice post-cytarabine treatment. Notably, LAMA4 inhibition or knockdown in human MSCs promoted human AML cell proliferation and chemoprotection. Together, our study for the first time demonstrates the critical role of Lama4 in impeding AML progression and chemoresistance. Targeting Lama4 signaling pathways may offer potential new therapeutic options for AML.

Ribonucleotide reductase inhibitors suppress SAMHD1 ara-CTPase activity enhancing cytarabine efficacy.

The deoxycytidine analogue cytarabine (ara-C) remains the backbone treatment of acute myeloid leukaemia (AML) as well as other haematological and lymphoid malignancies, but must be combined with other chemotherapeutics to achieve cure. Yet, the underlying mechanism dictating synergistic efficacy of combination chemotherapy remains largely unknown. The dNTPase SAMHD1, which regulates dNTP homoeostasis antagonistically to ribonucleotide reductase (RNR), limits ara-C efficacy by hydrolysing the active triphosphate metabolite ara-CTP. Here, we report that clinically used inhibitors of RNR, such as gemcitabine and hydroxyurea, overcome the SAMHD1-mediated barrier to ara-C efficacy in primary blasts and mouse models of AML, displaying SAMHD1-dependent synergy with ara-C. We present evidence that this is mediated by dNTP pool imbalances leading to allosteric reduction of SAMHD1 ara-CTPase activity. Thus, SAMHD1 constitutes a novel biomarker for combination therapies of ara-C and RNR inhibitors with immediate consequences for clinical practice to improve treatment of AML.

A radical switch in clonality reveals a stem cell niche in the epiphyseal growth plate.

Longitudinal bone growth in children is sustained by growth plates, narrow discs of cartilage that provide a continuous supply of chondrocytes for endochondral ossification1. However, it remains unknown how this supply is maintained throughout childhood growth. Chondroprogenitors in the resting zone are thought to be gradually consumed as they supply cells for longitudinal growth1,2, but this model has never been proved. Here, using clonal genetic tracing with multicolour reporters and functional perturbations, we demonstrate that longitudinal growth during the fetal and neonatal periods involves depletion of chondroprogenitors, whereas later in life, coinciding with the formation of the secondary ossification centre, chondroprogenitors acquire the capacity for self-renewal, resulting in the formation of large, stable monoclonal columns of chondrocytes. Simultaneously, chondroprogenitors begin to express stem cell markers and undergo symmetric cell division. Regulation of the pool of self-renewing progenitors involves the hedgehog and mammalian target of rapamycin complex 1 (mTORC1) signalling pathways. Our findings indicate that a stem cell niche develops postnatally in the epiphyseal growth plate, which provides a continuous supply of chondrocytes over a prolonged period.

Distinct roles of mesenchymal stem and progenitor cells during the development of acute myeloid leukemia in mice.

Despite increasing evidence for the involvement of bone marrow (BM) hematopoietic stem cell niche in leukemogenesis, how BM mesenchymal stem and progenitor cells (MSPCs) contribute to leukemia niche formation and progression remains unclear. Using an MLL-AF9 acute myeloid leukemia (AML) mouse model, we demonstrate dynamic alterations of BM cellular niche components, including MSPCs and endothelial cells during AML development and its association with AML engraftment. Primary patient AML cells also induced similar niche alterations in xenografted mice. AML cell infiltration in BM causes an expansion of early B-cell factor 2+ (Ebf2+) MSPCs with reduced Cxcl12 expression and enhanced generation of more differentiated mesenchymal progenitor cells. Importantly, in vivo fate-mapping indicates that Ebf2+ MSPCs participated in AML niche formation. Ebf2+ cell deletion accelerated the AML development. These data suggest that native BM MSPCs may suppress AML. However, they can be remodeled by AML cells to form leukemic niche that might contribute to AML progression. AML induced dysregulation of hematopoietic niche factors like Angptl1, Cxcl12, Kitl, Il6, Nov, and Spp1 in AML BM MSPCs, which was associated with AML engraftment and partially appeared before the massive expansion of AML cells, indicating the possible involvement of the niche factors in AML progression. Our study demonstrates distinct dynamic features and roles of BM MSPCs during AML development.

Sipa1 deficiency-induced bone marrow niche alterations lead to the initiation of myeloproliferative neoplasm.

Mutations of signal-induced proliferation-associated gene 1 (SIPA1), a RAP1 GTPase-activating protein, were reported in patients with juvenile myelomonocytic leukemia, a childhood myelodysplastic/myeloproliferative neoplasm (MDS/MPN). Sipa1 deficiency in mice leads to the development of age-dependent MPN. However, Sipa1 expression in bone marrow (BM) microenvironment and its effect on the pathogenesis of MPN remain unclear. We here report that Sipa1 is expressed in human and mouse BM stromal cells and downregulated in these cells from patients with MPN or MDS/MPN at diagnosis. By using the Sipa1-/- MPN mouse model, we find that Sipa1 deletion causes phenotypic and functional alterations of BM mesenchymal stem and progenitor cells prior to the initiation of the MPN. Importantly, the altered Sipa1-/- BM niche is required for the development of MDS/MPN following transplantation of normal hematopoietic cells. RNA sequencing reveals an enhanced inflammatory cytokine signaling and dysregulated Dicer1, Kitl, Angptl1, Cxcl12, and Thpo in the Sipa1-/- BM cellular niches. Our data suggest that Sipa1 expression in the BM niche is critical for maintaining BM niche homeostasis. Moreover, Sipa1 loss-induced BM niche alterations likely enable evolution of clonal hematopoiesis to the hematological malignancies. Therefore, restoring Sipa1 expression or modulating the altered signaling pathways involved might offer therapeutic potential for MPN.

CD36 Is a Marker of Human Adipocyte Progenitors with Pronounced Adipogenic and Triglyceride Accumulation Potential.

White adipose tissue (WAT) expands in part through adipogenesis, a process involving fat cell generation and fatty acid (FA) storage into triglycerides (TGs). Several findings suggest that inter-individual and regional variations in adipogenesis are linked to metabolic complications. We aimed to identify cellular markers that define human adipocyte progenitors (APs) with pronounced adipogenic/TG storage ability. Using an unbiased single cell screen of passaged human adipose-derived stromal cells (hADSCs), we identified cell clones with similar proliferation rates but discordant capabilities to undergo adipogenic differentiation. Transcriptomic analyses prior to induction of differentiation showed that adipogenic clones displayed a significantly higher expression of CD36, encoding the scavenger receptor CD36. CD36+ hADSCs, in comparison with CD36-cells, displayed almost complete adipogenic differentiation while CD36 RNAi attenuated lipid accumulation. Similar findings were observed in primary CD45-/CD34+/CD31-APs isolated from human WAT where the subpopulation of MSCA1+/CD36+ cells displayed a significantly higher differentiation degree/TG storage capacity than MSCA1+/CD36-cells. Functional analyses in vitro and ex vivo confirmed that CD36 conferred APs an increased capacity to take up FAs thereby facilitating terminal differentiation. Among primary APs from subcutaneous femoral, abdominal and visceral human WAT, the fraction of CD36+ cells was significantly higher in depots associated with higher adipogenesis and reduced metabolic risk (i.e., femoral WAT). We conclude that CD36 marks APs with pronounced adipogenic potential, most probably by facilitating lipid uptake. This may be of value in developing human adipocyte cell clones and possibly in linking regional variations in adipogenesis to metabolic phenotype. Stem Cells 2017;35:1799-1814.

Progenitor Hematopoietic Cells Implantation Improves Functional Capacity of End Stage Coronary Artery Disease Patients with Advanced Heart Failure.

Background. Proangiogenic Hematopoietic Cells (PHC) which comprise diverse mixture of cell types are able to secrete proangiogenic factors and interesting candidate for cell therapy. The aim of this study was to seek for benefit in implantation of PHC on functional improvement in end stage coronary artery disease patients with advanced heart failure. Methods. Patients with symptomatic heart failure despite guideline directed medical therapy and LVEF less than 35% were included. Peripheral blood mononuclear cells were isolated, cultivated for 5 days, and then harvested. Flow cytometry and cell surface markers were used to characterize PHC. The PHC were delivered retrogradely via sinus coronarius. Echocardiography, myocardial perfusion, and clinical and functional data were analyzed up to 1-year observation. Results. Of 30 patients (56.4 ± 7.40 yo) preimplant NT proBNP level is 5124.5 ± 4682.50 pmol/L. Harvested cells characterized with CD133, CD34, CD45, and KDR showed 0.87 ± 0.41, 0.63 ± 0.66, 99.00 ± 2.60, and 3.22 ± 3.79%, respectively. LVEF was improved (22 ± 5.68 versus 26.8 ± 7.93, p < 0.001) during short and long term observation. Myocardial perfusion significantly improved 6 months after treatment. NYHA Class and six-minute walk test are improved during short term and long term follow-up. Conclusion. Expanded peripheral blood PHC implantation using retrograde delivery approach improved LV systolic function, myocardial perfusion, and functional capacity.

Isolation and cultivation of mesenchymal stem cells from iliac crest bone marrow for further cartilage defect management.

AIM: to validate isolation and cultivation methods of bone marrow mesenchymal stem cells (BM-MSCs) from iliac crest, and to compare biological characteristics of BM-MSCs from different age groups for preparation of autologous stem cell therapy in cartilage defect. METHODS: patients undergoing spinal surgery were selected and grouped according to age. Iliac crest bone marrow from the patients was aspirated. BM-MSCs were isolated from the bone marrow and then cultivated. Their biological characteristics including morphological appearances and surface biomarkers were evaluated. Growth curves were observed. Sterility and Mycoplasma tests were also performed for quality assessment of BM-MSCs culture procedure. RESULTS: in average, cultivated-BM-MSCs reached the number of 7.56-22.95 x 106 in 4-7 weeks period. BM-MSCs of all age groups showed the same quality of morphology, shape and surface biomarkers (CD105+, CD73+, CD34-, CD45-, CD14-, CD19-, HLA-DR-). CONCLUSION: our procedures in isolating and cultivating of BM-MSCs have reached required amount for implantation into the cartilage lesion. In addition, the cultivated-BM-MSCs' biological characteristics were also in accordance with International Society of Cell Therapy (ISCT) MSCs criteria.