Comprehensive characterization of mesenchymal stromal cells from patients with Fanconi anaemia

Circulating Mesenchymal Stromal Cells in Patients with Infantile Hemangioma: Evaluation of Their Functional Capacity and Gene Expression Profile

We previously published that in patients with infantile hemangioma (IH) at the onset (T0) colony forming unit-fibroblasts (CFU-Fs) are present in in vitro cultures from PB. Herein, we characterize these CFU-Fs and investigate their potential role in IH pathogenesis, before and after propranolol therapy. The CFU-F phenotype (by flow cytometry), their differentiation capacity and ability to support angiogenesis (by in vitro cultures) and their gene expression (by RT-PCR) were evaluated. We found that CFU-Fs are actual circulating MSCs (cMSCs). In patients at T0, cMSCs had reduced adipogenic potential, supported the formation of tube-like structures in vitro and showed either inflammatory (IL1β and ESM1) or angiogenic (F3) gene expression higher than that of cMSCs from CTRLs. In patients receiving one-year propranolol therapy, the cMSC differentiation in adipocytes improved, while their support in in vitro tube-like formation was lost; no difference was found between patient and CTRL cMSC gene expressions. In conclusion, in patients with IH at T0 the cMSC reduced adipogenic potential, their support in angiogenic activity and the inflammatory/angiogenic gene expression may fuel the tumor growth. One-year propranolol therapy modifies this picture, suggesting cMSCs as one of the drug targets.

Multiparametric analysis of etoposide exposed mesenchymal stem cells and Fanconi anemia cells: implications in development of secondary myeloid malignancy

Secondary acute myeloid leukemia (sAML) may develop following a prior therapy or may evolve from an antecedent hematological disorder such as Fanconi Anemia (FA). Pathophysiology of leukemic evolution is not clear. Etoposide (Eto) is a chemotherapeutic agent implicated in development of sAML. FA is an inherited bone marrow (BM) failure disease characterized by genomic instability and xenobiotic susceptibility. Here, we hypothesized that alterations in the BM niche may play a critical/driver role in development of sAML in both conditions. Expression of selected genes involved in xenobiotic metabolism, DNA double-strand break response, endoplasmic reticulum (ER) stress, heat shock response and cell cycle regulation were determined in BM mesenchymal stem cells (MSCs) of healthy controls and FA patients at steady state and upon exposure to Eto at different concentrations and in recurrent doses. Expression of CYPA1, p53, CCNB1, Dicer1, CXCL12, FLT3L and TGF-Beta genes were significantly downregulated in FA-MSCs compared with healthy controls. Eto exposure induced significant alterations in healthy BM-MSCs with increased expression of CYP1A1, GAD34, ATF4, NUPR1, CXCL12, KLF4, CCNB1 and nuclear localization of Dicer1. Interestingly, FA-MSCs did not show significant alterations in these genes upon Eto exposure. As opposed to healthy MSCs DICER1 gene expression and intracellular localization was not altered on FA BM-MSCs after Eto treatment. These results showed that Eto is a highly potent molecule and has pleiotropic effects on BM-MSCs, FA cells show altered expression profile compared to healthy controls and Eto exposure on FA cells shows differential profile than healthy controls.

Fanca deficiency is associated with alterations in osteoclastogenesis that are rescued by TNFα

BACKGROUND

Hematopoietic stem cells (HSCs) reside in the bone marrow (BM) niche, which includes bone-forming and bone-resorbing cells, i.e., osteoblasts (OBs) and osteoclasts (OCs). OBs originate from mesenchymal progenitors, while OCs are derived from HSCs. Self-renewal, proliferation and differentiation of HSCs are under the control of regulatory signals generated by OBs and OCs within the BM niche. Consequently, OBs and OCs control both bone physiology and hematopoiesis. Since the human developmental and bone marrow failure genetic syndrome fanconi anemia (FA) presents with skeletal abnormalities, osteoporosis and HSC impairment, we wanted to test the hypothesis that the main pathological abnormalities of FA could be related to a defect in OC physiology and/or in bone homeostasis.

RESULTS

We revealed here that the intrinsic differentiation of OCs from a Fanca^-/- mouse is impaired in vitro due to overactivation of the p53-p21 axis and defects in NF-kB signaling. The OC differentiation abnormalities observed in vitro were rescued by treating Fanca^-/- cells with the p53 inhibitor pifithrin-α, by treatment with the proinflammatory cytokine TNFα or by coculturing them with Fanca-proficient or Fanca-deficient osteoblastic cells.

CONCLUSIONS

Overall, our results highlight an unappreciated role of Fanca in OC differentiation that is potentially circumvented in vivo by the presence of OBs and TNFα in the BM niche.

Lung mesenchymal cells from patients with COVID-19 driven lung fibrosis: Several features with CTD-ILD derived cells but with higher response to fibrogenic signals and might be more pro-inflammatory

A subset of severe COVID19 patients develop pulmonary fibrosis, but the pathophysiology of this complication is still unclear. We previously described the possibility to isolate lung mesenchymal cells (LMC) by culturing broncho-alveolar lavage (BAL) cells from patients with pulmonary fibrosis or chronic lung allograft dysfunction. Aim of this study was to investigate the possibility to isolate and characterize LMC from BAL of patients that, two months after discharge for severe COVID19, show CT signs of post-COVID19 fibrosis (Post-COVID) and in some cases has been considered transplant indication. Results were compared with those from BAL of patients with collagen tissue disease-associated interstitial fibrosis (CTD-ILD). BAL fluid levels of TGFβ, VEGF, TIMP2, RANTES, IL6, IL8, and PAI1 were assessed. LMC were cultured and expanded, phenotyped by flow cytometry, and tested for osteogenic and adipogenic differentiation. Finally, we tested immunomodulatory and proliferative capabilities, collagen I production + /- TGF-beta stimulation. BAL cytokine and growth factor levels were comparable in the two groups. Efficiency of isolation from BAL was 100% in post-COVID compared to 63% in CTD-ILD. LMC from post-COVID were positive for CD105, CD73, CD90, and negative for CD45, CD34, CD19 and HLA-DR as in CTD-ILD samples. Post-COVID LMC displayed higher collagen production with respect to CTD-ILD LMC. Immunomodulatory capacity towards lymphocytes was very low, while Post-COVID LMC significantly upregulated pro-inflammatory cytokine production by healthy PBMCs. Our preliminary data suggest that LMC from post-COVID19 fibrosis patients share several features with CTD-ILD ones but might have a higher response to fibrogenic signals and pro-inflammatory profile.

Mesenchymal stem/stromal cells from a transplanted, asymptomatic patient with Fanconi anemia exhibit an aging-like phenotype and dysregulated expression of genes implicated in hematopoiesis and myelodysplasia

BACKGROUND AIMS

Fanconi anemia (FA) is an inherited bone marrow failure syndrome caused by defects in the repair of DNA inter-strand crosslinks and manifests as aplastic anemia, myelodysplastic syndrome and acute myeloid leukemia. FA also causes defects in mesenchymal stromal cell (MSC) function, but how different FA gene mutations alter function remains understudied.

METHODS

We compared the growth, differentiation and transcript profile of a single MSC isolate from an asymptomatic patient with FA with a FANCG nonsense mutation who underwent hematopoietic stem cell transplantation 10 years prior to that from a representative healthy donor (HD).

RESULTS

We show that FANCG-/- MSCs exhibit rapid onset of growth cessation, skewed bi-lineage differentiation in favor of adipogenesis and increased cellular oxidate stress consistent with an aging-like phenotype. Transcript profiling identified pathways related to cell growth, senescence, cellular stress responses and DNA replication/repair as over-represented in FANCG-/- MSC, and real-time polymerase chain reaction confirmed these MSCs expressed reduced levels of transcripts implicated in cell growth (TWIST1, FGFR2v7-8) and osteogenesis (TWIST1, RUNX2) and increased levels of transcripts regulating adipogenesis (GPR116) and insulin signaling. They also expressed reduced levels of mRNAs implicated in HSC self-maintenance and homing (KITLG, HGF, GDNF, PGF, CFB, IL-1B and CSF1) and elevated levels of those implicated in myelodysplasia (IL-6, GDF15).

CONCLUSIONS

Together, these findings demonstrate how inactivation of FANCG impacts MSC behavior, which parallels observed defects in osteogenesis, HSC depletion and leukemic blast formation seen in patients with FA.

Somatic mosaicism in patients with Fanconi anaemia: Proposal of alternative tissue for inconclusive diagnoses

INTRODUCTION

Fanconi anaemia (FA) is a rare genetic disorder marked by progressive bone marrow failure, chromosomal fragility, and increased cancer susceptibility. Laboratory diagnosis includes chromosomal instability test and mutation investigation. A total of 15%-25% of all patients may have somatic mosaicism, characterized by two distinct haematopoietic cell populations, one resistant and one sensitive to agents that induce chromosomal breakage, which complicates the diagnosis by a high incidence of reverted cells leading to inconclusive or false-negative results. The study aimed to evaluate the use of bone marrow stromal mesenchymal cells (BM-MSCs) as an alternative, non-haematopoietic tissue for diagnosis.

METHODS

Bone marrow mesenchymal stromal cells from 12 patients with positive diepoxybutane (DEB) tests were cultivated and analysed by cytogenetics and mutation investigation.

RESULTS

The DEB test was performed at 0.1 and 0.01 μg/ml concentrations, with an index ranging from 0.24 to 1.00. At higher concentration, the metaphases number was lower, probably due to toxicity. Regarding the molecular investigation, all the mutations previously found in peripheral blood were identified on BM-MSC.

CONCLUSION

This study demonstrated the possibility of using BM-MSCs as an alternative tissue for cytogenetic and molecular investigation. Future tests using an intermediate DEB concentration may lead to an optimal protocol that could be non-toxic to cells but provides conclusive results.

Bone Marrow Microenvironment in Light-Chain Amyloidosis: In Vitro Expansion and Characterization of Mesenchymal Stromal Cells

Immunoglobulin light-chain amyloidosis (AL) is caused by misfolded light chains produced by a small B cell clone. Mesenchymal stromal cells (MSCs) have been reported to affect plasma cell behavior. We aimed to characterize bone marrow (BM)-MSCs from AL patients, considering functional aspects, such as proliferation, differentiation, and immunomodulatory capacities. MSCs were in vitro expanded from the BM of 57 AL patients and 14 healthy donors (HDs). MSC surface markers were analyzed by flow cytometry, osteogenic and adipogenic differentiation capacities were in vitro evaluated, and co-culture experiments were performed in order to investigate MSC immunomodulatory properties towards the ALMC-2 cell line and HD peripheral blood mononuclear cells (PBMCs). AL-MSCs were comparable to HD-MSCs for morphology, immune-phenotype, and differentiation capacities. AL-MSCs showed a reduced proliferation rate, entering senescence at earlier passages than HD-MSCs. The AL-MSC modulatory effect on the plasma-cell line or circulating plasma cells was comparable to that of HD-MSCs. To our knowledge, this is the first study providing a comprehensive characterization of AL-MSCs. It remains to be defined if the observed abnormalities are the consequence of or are involved in the disease pathogenesis. BM microenvironment components in AL may represent the targets for the prevention/treatment of the disease in personalized therapies.

Mesenchymal Stem Cells in Aplastic Anemia and Myelodysplastic Syndromes: The "Seed and Soil" Crosstalk

There is growing interest in the contribution of the marrow niche to the pathogenesis of bone marrow failure syndromes, i.e., aplastic anemia (AA) and myelodysplastic syndromes (MDSs). In particular, mesenchymal stem cells (MSCs) are multipotent cells that contribute to the organization and function of the hematopoietic niche through their repopulating and supporting abilities, as well as immunomodulatory properties. The latter are of great interest in MDSs and, particularly, AA, where an immune attack against hematopoietic stem cells is the key pathogenic player. We, therefore, conducted Medline research, including all available evidence from the last 10 years concerning the role of MSCs in these two diseases. The data presented show that MSCs display morphologic, functional, and genetic alterations in AA and MDSs and contribute to immune imbalance, ineffective hematopoiesis, and leukemic evolution. Importantly, adoptive MSC infusion from healthy donors can be exploited to heal the "sick" niche, with even better outcomes if cotransplanted with allogeneic hematopoietic stem cells. Finally, future studies on MSCs and the whole microenvironment will further elucidate AA and MDS pathogenesis and possibly improve treatment.

The Phenotype and Functional Activity of Mesenchymal Stromal Cells in Pediatric Patients with Non-Malignant Hematological Diseases

As the biology of mesenchymal stromal cells (MSCs) in patients with non-malignant hematological diseases (NMHD) is poorly understood, in the current study we performed a basic characterization of the phenotype and functional activity of NMHD-MSCs. Bone marrow (BM) of patients with thalassemia major (TM) possessed a significantly higher number of nucleated cells (BM-MNCs)/mL BM than healthy donors (P < 0.0001), which however did not result in a higher number of colony forming units-fibroblast (CFU-F) per milliliter BM. In contrast, from 1 × 10⁶ BM-MNCs of patients with sickle cell disease (SCD) were generated significantly more CFU-Fs than from TM-BM-MNCs (P < 0.013) and control group (P < 0.02). In addition, NMHD-MSCs expressed significantly lower levels of CD146 molecule, demonstrated an equal proliferation potential and differentiated along three lineages (osteoblasts, chondrocytes and adipocytes) as healthy donors’ MSCs, with exception of TM-MSCs which differentiated weakly in adipocytes. In contrast to other NMHD-MSCs and healthy donors’ MSCs, TM-MSCs demonstrated an impaired in vitro immunosuppressive potential, either. Noteworthy, the majority of the immunosuppressive effect of NMHD-MSCs was mediated through prostaglandin-E2 (PGE2), because indomethacin (an inhibitor of PGE2 synthesis) was able to significantly reverse this effect. Our results indicate therefore that NMHD-MSCs, except TM-MSCs, may be used as an autologous cell-based therapy for post-transplant complications such as graft failure, graft-versus-host disease (GvHD) and osteonecrosis.

Genetic Stability of Mesenchymal Stromal Cells for Regenerative Medicine Applications: A Fundamental Biosafety Aspect

Mesenchymal stem/stromal cells (MSC) show widespread application for a variety of clinical conditions; therefore, their use necessitates continuous monitoring of their safety. The risk assessment of mesenchymal stem cell-based therapies cannot be separated from an accurate and deep knowledge of their biological properties and in vitro and in vivo behavior. One of the most relevant safety issues is represented by the genetic stability of MSCs, that can be altered during in vitro manipulation, frequently required before clinical application. MSC genetic stability has the potential to influence the transformation and the therapeutic effect of these cells. At present, karyotype evaluation represents the definitely prevailing assessment of MSC stability, but DNA alterations of smaller size should not be underestimated. This review will focus on current scientific knowledge about the genetic stability of mesenchymal stem cells. The techniques used and possible improvements together with regulatory aspects will also be discussed.

Pathogenesis of Acquired Aplastic Anemia and the Role of the Bone Marrow Microenvironment

Aplastic anemia (AA) is characterized by bone marrow (BM) hypocellularity, resulting in peripheral cytopenias. An antigen-driven and likely auto-immune dysregulated T-cell homeostasis results in hematopoietic stem cell injury, which ultimately leads to the pathogenesis of the acquired form of this disease. Auto-immune and inflammatory processes further influence the disease course as well as response rate to therapy, mainly consisting of intensive immunosuppressive therapy and allogeneic hematopoietic cell transplantation. Bone marrow hematopoietic stem and progenitor cells are strongly regulated by the crosstalk with the surrounding microenvironment and its components like mesenchymal stromal cells, also consistently altered in AA. Whether latter is a contributing cause or rather consequence of the disease remains an open question. Overall, niche disruption may contribute to disease progression, sustain pancytopenia and promote clonal evolution. Here we review the existing knowledge on BM microenvironmental changes in acquired AA and discuss their relevance for the pathogenesis and therapy.

Mesenchymal Stromal Cells: Role in the BM Niche and in the Support of Hematopoietic Stem Cell Transplantation

Mesenchymal stromal cells (MSCs) are key elements in the bone marrow (BM) niche where they interact with hematopoietic stem progenitor cells (HSPCs) by offering physical support and secreting soluble factors, which control HSPC maintenance and fate. Although necessary for their maintenance, MSCs are a rare population in the BM, they are plastic adherent and can be ex vivo expanded to reach numbers adequate for clinical use. In light of HSPC supportive properties, MSCs have been employed in phase I/II clinical trials of hematopoietic stem cell transplantation (HSCT) to facilitate engraftment of hematopoietic stem cells (HSCs). Moreover, they have been utilized to expand ex vivo HSCs before clinical use. The available clinical evidence from these trials indicate that MSC administration is safe, as no acute and long-term adverse events have been registered in treated patients, and may be efficacious in promoting hematopoietic engraftment after HSCT. In this review, we critically discuss the role of MSCs as component of the BM niche, as recent advances in defining different mesenchymal populations in the BM have considerably increased our understanding of this complex environment. Moreover, we will revise published literature on the use of MSCs to support HSC engraftment and expansion, as well as consider potential new MSC application in the clinical context of ex vivo gene therapy with autologous HSC.

Deletion of the Fanconi Anemia C Gene in Mice Leads to Skeletal Anomalies and Defective Bone Mineralization and Microarchitecture

Fanconi anemia (FA) is a rare genetic disorder associated with a progressive decline in hematopoietic stem cells leading to bone marrow failure. FA is also characterized by a variety of developmental defects including short stature and skeletal malformations. More than half of children affected with FA have radial-ray abnormalities, and many patients have early onset osteopenia/osteoporosis. Although many Fanconi anemia genes have been identified and a molecular pathway defined, the underlying mechanism leading to bone defects remains elusive. To understand the role of FA genes in skeletal development and bone microarchitecture, we evaluated bone physiology during embryogenesis and in adult FancA- and FancC-deficient mice. We found that both FancA^-/- and FancC^-/- embryos have abnormal skeletal development shown by skeletal malformations, growth delay, and reduced bone mineralization. FancC^-/- adult mice present altered bone morphology and microarchitecture with a significant decrease in cortical bone mineral density in a sex-specific manner. Mechanical testing revealed that male but not female FancC^-/- mice show reduced bone strength compared with their wild-type littermates. Ex vivo cultures showed that FancA^-/- and FancC^-/- bone marrow-derived mesenchymal stem cells (_BM MSC) have impaired differentiation capabilities together with altered gene expression profiles. Our results suggest that defective bone physiology in FA occurs in utero and possibly results from altered _BM MSC function. These results provide valuable insights into the mechanism involved in FA skeletal defects. © 2018 American Society for Bone and Mineral Research.

European experience and risk factor analysis of donor cell-derived leukaemias/MDS following haematopoietic cell transplantation

Donor cell leukaemia (DCL) is a rare complication of allogeneic haematopoietic cell transplantation (HCT). We have investigated the prevalence and outcome of donor cell haematology malignancies within centres registered with the European Society of Blood and Marrow transplantation (EBMT). We have sought to identify risk factors to shed light on the pathogenesis of DCL as a model for leukaemogenesis. DCL cases were identified by questionnaire and a follow-up questionnaire requested detailed data. Control subjects from the EBMT registry who had not developed DCL were used for a matched pair analysis to identify risk factors. We identified 38 patients with DCL; the estimated prevalence was 80.5/100,000 transplants. Patients were predominantly treated for haematological malignancy. A clone was retrospectively identified in 7/25 (28%) donors for whom data was available. Overall survival was poor with 29/38 patients dead a median of 11 (range 0-91) months after DCL diagnosis. Matched case-pair analysis identified three factors on multivariate analysis as significantly associated with an increased risk for DCL: use of growth factors within the first 100 days after transplantation, in vivo T-cell depletion and multiple allografts. The risk factors identified, support reduced immune surveillance and replicative stress as pathogenic in the development of DCL.

Reduced Cell Division Control Protein 42 Activity Compromises Hematopoiesis-Supportive Function of Fanconi Anemia Mesenchymal Stromal Cells

Hematopoietic stem cells preserve their ability to self-renew and differentiate to different lineages in the bone marrow (BM) niche, which is composed in large part by BM stromal cells. Studies have shown that altered signaling in the BM niche results in leukemia initiation or progression. Fanconi anemia (FA) is an inherited BM failure syndrome associated with extremely high risk of leukemic transformation. By using two FA mouse models, here we have investigated the hematopoiesis-supportive function of FA BM mesenchymal stroma cells (MSCs). We found that MSCs deficient for Fanca or Fancc gene are defective in proliferation and prone to undergo senescence in vitro. Mechanistically, we show that the activity of cell division control protein 42 (Cdc42), a Rho GTPase known to be a critical regulator for cytoskeleton organization, is significantly reduced in FA MSCs. Furthermore, we demonstrate that this reduction in Cdc42 activity plays a causal role in defective hematopoiesis-supportive function of the FA MSCs. The progenies of wild-type hematopoietic stem and progenitor cells cocultured on FA MSCs exhibit compromised self-renewal capacity both in vitro and in vivo. Genetic correction of FA deficiency restores Cdc42 activity and improves the hematopoiesis-supportive capacity of FA MSC. Finally, ectopic expression of a constitutively active Cdc42 mutant, Cdc42F28L, or pretreatment with Wnt5a, increases the active Cdc42 level and rescues the hematopoietic supportive defects of FA MSCs. Taken together, our results identify a novel link between Cdc42 activity and the hematopoiesis-supportive function of MSCs and suggest that a niche-specific increase of Cdc42 activity may be beneficial for FA therapy. Stem Cells 2018;36:785-795.

Hematopoietic development: a gap in our understanding of inherited bone marrow failure

Inherited bone marrow failure syndromes (IBMFS) represent a heterogeneous group of multisystem disorders that typically present with cytopenia in early childhood. Efforts to understand the underlying hematopoietic stem cell (HSC) losses have generally focused on postnatal hematopoiesis. However, reflecting the role of many of the involved genes in core cellular functions and the diverse nonhematologic abnormalities seen in patients at birth, studies have begun to explore IBMFS manifestations during fetal development. Here, I consider the current evidence for fetal deficits in the HSC pool and highlight emerging concepts regarding the origins and unique pathophysiology of hematopoietic failure in IBMFS.

Biological and functional characterization of bone marrow-derived mesenchymal stromal cells from patients affected by primary immunodeficiency

Mesenchymal stromal cells (MSCs) represent a key component of bone marrow (BM) microenvironment and display immune-regulatory properties. We performed a detailed analysis of biological/functional properties of BM-MSCs derived from 33 pediatric patients affected by primary immune-deficiencies (PID-MSCs): 7 Chronic Granulomatous Disease (CGD), 15 Wiskott-Aldrich Syndrome (WAS), 11 Severe Combined Immunodeficiency (SCID). Results were compared with MSCs from 15 age-matched pediatric healthy-donors (HD-MSCs). Clonogenic and proliferative capacity, differentiation ability, immunophenotype, immunomodulatory properties were analyzed. WB and RT-qPCR for CYBB, WAS and ADA genes were performed. All PID-MSCs displayed clonogenic and proliferative capacity, morphology and immunophenotype comparable with HD-MSCs. PID-MSCs maintained the inhibitory effect on T- and B-lymphocyte proliferation, except for decreased inhibitory ability of SCID-MSCs at MSC:PBMC ratio 1:10. While HD- and CGD-MSCs were able to inhibit monocyte maturation into immature dendritic cells, in SCID- and WAS-MSCs this ability was reduced. After Toll-like Receptor priming, PID-MSCs displayed in vitro an altered gene expression profile of pro- and anti-inflammatory soluble factors. PID-MSCs displayed lower PPARγ levels and WAS- and SCID-MSCs higher levels of key osteogenic markers, as compared with HD-MSCs. Our results indicate that PID-MSCs may be defective in some functional abilities; whether these defects contribute to disease pathophysiology deserves further investigation.

An abnormal bone marrow microenvironment contributes to hematopoietic dysfunction in Fanconi anemia

Fanconi anemia is a complex heterogeneous genetic disorder with a high incidence of bone marrow failure, clonal evolution to acute myeloid leukemia and mesenchymal-derived congenital anomalies. Increasing evidence in Fanconi anemia and other genetic disorders points towards an interdependence of skeletal and hematopoietic development, yet the impact of the marrow microenvironment in the pathogenesis of the bone marrow failure in Fanconi anemia remains unclear. Here we demonstrated that mice with double knockout of both Fancc and Fancg genes had decreased bone formation at least partially due to impaired osteoblast differentiation from mesenchymal stem/progenitor cells. Mesenchymal stem/progenitor cells from the double knockout mice showed impaired hematopoietic supportive activity. Mesenchymal stem/progenitor cells of patients with Fanconi anemia exhibited similar cellular deficits, including increased senescence, reduced proliferation, impaired osteoblast differentiation and defective hematopoietic stem/progenitor cell supportive activity. Collectively, these studies provide unique insights into the physiological significance of mesenchymal stem/progenitor cells in supporting the marrow microenvironment, which is potentially of broad relevance in hematopoietic stem cell transplantation.

A FANCD2/FANCI-Associated Nuclease 1-Knockout Model Develops Karyomegalic Interstitial Nephritis

Karyomegalic interstitial nephritis (KIN) is a chronic interstitial nephropathy characterized by tubulointerstitial nephritis and formation of enlarged nuclei in the kidneys and other tissues. We recently reported that recessive mutations in the gene encoding FANCD2/FANCI-associated nuclease 1 (FAN1) cause KIN in humans. FAN1 is a major component of the Fanconi anemia-related pathway of DNA damage response (DDR) signaling. To study the pathogenesis of KIN, we generated a Fan1 knockout mouse model, with abrogation of Fan1 expression confirmed by quantitative RT-PCR. Challenging Fan1^-/- and wild-type mice with 20 mg/kg cisplatin caused AKI in both genotypes. In contrast, chronic injection of cisplatin at 2 mg/kg induced KIN that led to renal failure within 5 weeks in Fan1^-/- mice but not in wild-type mice. Cell culture studies showed decreased survival and reduced colony formation of Fan1^-/- mouse embryonic fibroblasts and bone marrow mesenchymal stem cells compared with wild-type counterparts in response to treatment with genotoxic agents, suggesting that FAN1 mutations cause chemosensitivity and bone marrow failure. Our data show that Fan1 is involved in the physiologic response of kidney tubular cells to DNA damage, which contributes to the pathogenesis of CKD. Moreover, Fan1^-/- mice provide a new model with which to study the pathomechanisms of CKD.