Isabelle Petit

Pluripotent Stem Cell Model Reveals Essential Roles for miR‐450b‐5p and miR‐184 in Embryonic Corneal Lineage Specification

Approximately 6 million people worldwide are suffering from severe visual impairments or blindness due to corneal diseases. Corneal allogeneic transplantation is often required to restore vision; however, shortage in corneal grafts and immunorejections remain major challenges. The molecular basis of corneal diseases is poorly understood largely due to lack of appropriate cellular models. Here, we described a robust differentiation of human‐induced pluripotent stem cells (hiPSCs) derived from hair follicles or skin fibroblasts into corneal epithelial‐like cells. We found that BMP4, coupled with corneal fibroblast‐derived conditioned medium and collagen IV allowed efficient corneal epithelial commitment of hiPSCs in a manner that recapitulated corneal epithelial lineage development with high purity. Organotypic reconstitution assays suggested the ability of these cells to stratify into a corneal‐like epithelium. This model allowed us identifying miR‐450b‐5p as a molecular switch of Pax6, a major regulator of eye development. miR‐450b‐5p and Pax6 were reciprocally distributed at the presumptive epidermis and ocular surface, respectively. miR‐450b‐5p inhibited Pax6 expression and corneal epithelial fate in vitro, altogether, suggesting that by repressing Pax6, miR‐450b‐5p triggers epidermal specification of the ectoderm, while its absence allows ocular epithelial development. Additionally, miR‐184 was detectable in early eye development and corneal epithelial differentiation of hiPSCs. The knockdown of miR‐184 resulted in a decrease in Pax6 and K3, in line with recent findings showing that a point mutation in miR‐184 leads to corneal dystrophy. Altogether, these data indicate that hiPSCs are valuable for modeling corneal development and may pave the way for future cell‐based therapy. STEM CELLS 2012;30:898–909

Protective roles of polyethylene glycol and trimetazidine against cold ischemia and reperfusion injuries of pig kidney graft.

Ischemia‐reperfusion injury (IRI) represents an allo‐independent risk factor which favors chronic allograft nephropathy (CAN). Here we analyzed the influence of preservation solutions on the function of autotransplanted pig kidneys over 1–16 weeks after surgery. Kidneys were cold‐flushed and cold‐stored for 24 or 48 h either in University of Wisconsin (UW), modified‐UW Hôpital Edouard Herriot, polyethylene glycol 20 kDa (PEG)‐supplemented preservation solutions with low K+ (ECPEG) or high K+ (ICPEG) content. Animals autotransplanted with kidneys cold‐stored for 24 h in ECPEG exhibited the greatest levels of creatinine clearance (Ccr: 161 ± 12 mL/min, n = 10) and the lowest levels of proteinuria (0.5 ± 0.03 mg/mL) 16 weeks after surgery as compared with pigs autotransplanted with kidneys cold‐stored in the other solutions tested (Ccr ranging from 80 and 140 mL/min). Similar differences, but with lower Ccr levels, were achieved after a prolonged period of cold‐storage(48 h). ECPEG better preserved the kidneys from monocytes/macrophages and CD4+ T cells infiltrations, VCAM‐1 and MHC class II overexpressions and occurrence of renal interstitial fibrosis (2%) as compared with the other preservation solutions (5%–20%). Adding the anti‐ischemic drug trimetazidine (TMZ) to the preservation solutions, particularly ECPEG, further improved the quality of the week‐16 post‐transplanted kidneys (Ccr: 182 ± 12 mL/min, n = 10). These findings demonstrated that adding PEG to extracellular‐like (with low K+ content) preservation solutions in combination with TMZ significantly improved the long‐term outcome of kidney grafts in this model of autotransplanted pig kidney.

Polyethylene Glycol Reduces Early and Long-Term Cold Ischemia-Reperfusion and Renal Medulla Injury

Ischemia-reperfusion injury (IRI) after transplantation is a major cause of delayed graft function, which has a negative impact on early and late graft function and improve acute rejection. We have previously shown that polyethylene glycol (PEG) and particularly PEG 20M has a protective effect against cold ischemia and reperfusion injury in an isolated perfused pig and rat kidney model. We extended those observations to investigate the role of PEG using different doses (30g or 50g/l) added (ICPEG30 or ICPEG50) or not (IC) to a simplified preservation solution to reduce IRI after prolonged cold storage (48-h) of pig kidneys when compared with Euro-Collins and University of Wisconsin solutions. The study of renal function and medulla injury was performed with biochemical methods and proton NMR spectroscopy. Histological and inflammatory cell studies were performed after reperfusion (30–40 min) and on days 7 and 14 and weeks 4, 8, and 12. Peripheral-type benzodiazepine receptor (PBR), a mitochondrial protein involved in cholesterol homeostasis, was also studied. The results demonstrated that ICPEG30 improved renal function and reduced medulla injury. ICPEG30 also improved tubular function and strongly protect mitochondrial integrity. Post-IRI inflammation was strongly reduced in this group, particularly lymphocytes TCD4+, PBR expression was influenced by IRI in the early period and during the development of chronic dysfunction. This study clearly shows that PEG has a beneficial effect in renal preservation and suggests a role of PBR as a marker IRI and repair processes.

Can inhibition of the SDF-1/CXCR4 axis eradicate acute leukemia?

Poor prognosis of acute leukemia with current treatments is mainly due to the relapse of the disease following chemotherapy. In the last decade, an emerging concept has proposed that the leukemia stem cells (LSCs) and their interactions with the BM microenvironment are the major cause of the acute leukemia relapse. Adhesion to the stromal niche is crucial for LSCs as it directly supports self-renewal, proliferation, arrest of differentiation and protects from damaging chemo-agents. One of the key players in this crosstalk between leukemic cells and the BM stroma niche is the chemokine SDF-1. SDF-1 regulates the process of homing and engraftment of LSCs into the BM and inhibition of its receptor CXCR4 induces leukemic cell mobilization into the circulation. However, besides its chemotactic and adhesive functions, SDF-1 is also a pleiotropic cytokine that regulates leukemic cell proliferation as well as their program of differentiation. CXCR4 antagonists are used in combination with chemotherapy in preclinical and clinical studies, which demonstrate that blocking CXCR4 is a novel promising approach of therapy. In this review, we focus on the multifaceted SDF-1/CXCR4 axis in acute leukemia and discuss how targeting this pathway could provide potential interest to eradicate the LSCs.

Evidence for a mitochondrial impact of trimetazidine during cold ischemia and reperfusion.

In organ transplantation, ischemia-reperfusion injury (IRI) has been implicated in delayed graft function (DGF) as well as in short- and long-term complications. Using an autotransplant pig kidney model, changes in renal function and morphology were determined after different periods of cold ischemia in kidneys preserved in the University of Wisconsin solution (UW), high-Na+ version of UW (HEH) or Celsior (CEL) a newly developed high-Na+ solution, with or without trimetazidine (TMZ). Kidney function was better preserved in CEL, UW and particularly HEH in combination with TMZ, particularly after 48 and 72 h. Mitochondria integrity was improved in TMZ-preserved groups. This study indicates that TMZ is efficiently protective against IRI even after prolonged preservation and in different preservation solutions.

RBM28, a protein deficient in ANE syndrome, regulates hair follicle growth via miR-203 and p63

Alopecia–neurological defects–endocrinopathy (ANE) syndrome is a rare inherited hair disorder, which was shown to result from decreased expression of the RNA‐binding motif protein 28 (RBM28). In this study, we attempted to delineate the role of RBM28 in hair biology. First, we sought to obtain evidence for the direct involvement of RBM28 in hair growth. When RBM28 was downregulated in human hair follicle (HF) organ cultures, we observed catagen induction and HF growth arrest, indicating that RBM28 is necessary for normal hair growth. We also aimed at identifying molecular targets of RBM28. Given that an RBM28 homologue was recently found to regulate miRNA biogenesis in C. elegans and given the known pivotal importance of miRNAs for proper hair follicle development, we studied global miRNA expression profile in cells knocked down for RBM28. This analysis revealed that RBM28 controls the expression of miR‐203. miR‐203 was found to regulate in turn TP63, encoding the transcription factor p63, which is critical for hair morphogenesis. In conclusion, RBM28 contributes to HF growth regulation through modulation of miR‐203 and p63 activity.

Modeling of Aniridia‐Related Keratopathy by CRISPR/Cas9 Genome Editing of Human Limbal Epithelial Cells and Rescue by Recombinant PAX6 Protein

Heterozygous PAX6 gene mutations leading to haploinsufficiency are the main cause of congenital aniridia, a rare and progressive panocular disease characterized by reduced visual acuity. Up to 90% of patients suffer from aniridia‐related keratopathy (ARK), caused by a combination of factors including limbal epithelial stem cell (LSC) deficiency, impaired healing response and abnormal differentiation of the corneal epithelium. It usually begins in the first decade of life, resulting in recurrent corneal erosions, sub‐epithelial fibrosis, and corneal opacification. Unfortunately, there are currently no efficient treatments available for these patients and no in vitro model for this pathology. We used CRISPR/Cas9 technology to introduce into the PAX6 gene of LSCs a heterozygous nonsense mutation found in ARK patients. Nine clones carrying a p.E109X mutation on one allele were obtained with no off‐target mutations. Compared with the parental LSCs, heterozygous mutant LSCs displayed reduced expression of PAX6 and marked slow‐down of cell proliferation, migration and detachment. Moreover, addition to the culture medium of recombinant PAX6 protein fused to a cell penetrating peptide was able to activate the endogenous PAX6 gene and to rescue phenotypic defects of mutant LSCs, suggesting that administration of such recombinant PAX6 protein could be a promising therapeutic approach for aniridia‐related keratopathy. More generally, our results demonstrate that introduction of disease mutations into LSCs by CRISPR/Cas9 genome editing allows the creation of relevant cellular models of ocular disease that should greatly facilitate screening of novel therapeutic approaches. Stem Cells 2018;36:1421–1429