A case report: Bone marrow mesenchymal stem cells from a rett syndrome patient are prone to senescence and show a lower degree of apoptosis

Altered Bone Status in Rett Syndrome

Rett syndrome (RTT) is a monogenic neurodevelopmental disorder primarily caused by mutations in X-linked MECP2 gene, encoding for methyl-CpG binding protein 2 (MeCP2), a multifaceted modulator of gene expression and chromatin organization. Based on the type of mutation, RTT patients exhibit a broad spectrum of clinical phenotypes with various degrees of severity. In addition, as a complex multisystem disease, RTT shows several clinical manifestations ranging from neurological to non-neurological symptoms. The most common non-neurological comorbidities include, among others, orthopedic complications, mainly scoliosis but also early osteopenia/osteoporosis and a high frequency of fractures. A characteristic low bone mineral density dependent on a slow rate of bone formation due to dysfunctional osteoblast activity rather than an increase in bone resorption is at the root of these complications. Evidence from human and animal studies supports the idea that MECP2 mutation could be associated with altered epigenetic regulation of bone-related factors and signaling pathways, including SFRP4/WNT/β-catenin axis and RANKL/RANK/OPG system. More research is needed to better understand the role of MeCP2 in bone homeostasis. Indeed, uncovering the molecular mechanisms underlying RTT bone problems could reveal new potential pharmacological targets for the treatment of these complications that adversely affect the quality of life of RTT patients for whom the only therapeutic approaches currently available include bisphosphonates, dietary supplements, and physical activity.

Modeling Rett Syndrome with Human Pluripotent Stem Cells: Mechanistic Outcomes and Future Clinical Perspectives

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the gene encoding the methyl-CpG-binding protein 2 (MeCP2). Among many different roles, MeCP2 has a high phenotypic impact during the different stages of brain development. Thus, it is essential to intensively investigate the function of MeCP2, and its regulated targets, to better understand the mechanisms of the disease and inspire the development of possible therapeutic strategies. Several animal models have greatly contributed to these studies, but more recently human pluripotent stem cells (hPSCs) have been providing a promising alternative for the study of RTT. The rapid evolution in the field of hPSC culture allowed first the development of 2D-based neuronal differentiation protocols, and more recently the generation of 3D human brain organoid models, a more complex approach that better recapitulates human neurodevelopment in vitro. Modeling RTT using these culture platforms, either with patient-specific human induced pluripotent stem cells (hiPSCs) or genetically-modified hPSCs, has certainly contributed to a better understanding of the onset of RTT and the disease phenotype, ultimately allowing the development of high throughput drugs screening tests for potential clinical translation. In this review, we first provide a brief summary of the main neurological features of RTT and the impact of MeCP2 mutations in the neuropathophysiology of this disease. Then, we provide a thorough revision of the more recent advances and future prospects of RTT modeling with human neural cells derived from hPSCs, obtained using both 2D and organoids culture systems, and its contribution for the current and future clinical trials for RTT.

Impaired mitochondrial quality control in Rett Syndrome

Rett Syndrome (RTT) is a rare neurodevelopmental disorder caused in the 95% of cases by mutations in the X-linked MECP2 gene, affecting almost exclusively females. While the genetic basis of RTT is known, the exact pathogenic mechanisms that lead to the broad spectrum of symptoms still remain enigmatic. Alterations in the redox homeostasis have been proposed among the contributing factors to the development and progression of the syndrome. Mitochondria appears to play a central role in RTT oxidative damage and a plethora of mitochondrial defects has already been recognized. However, mitochondrial dynamics and mitophagy, which represent critical pathways in regulating mitochondrial quality control (QC), have not yet been investigated in RTT. The present work showed that RTT fibroblasts have networks of hyperfused mitochondria with morphological abnormalities and increased mitochondrial volume. Moreover, analysis of mitophagic flux revealed an impaired PINK1/Parkin-mediated mitochondrial removal associated with an increase of mitochondrial fusion proteins Mitofusins 1 and 2 (MFN1 and 2) and a decrease of fission mediators including Dynamin related protein 1 (DRP1) and Mitochondrial fission 1 protein (FIS1). Finally, challenging RTT fibroblasts with FCCP and 2,4-DNP did not trigger a proper apoptotic cell death due to a defective caspase 3/7 activation. Altogether, our findings shed light on new aspects of mitochondrial dysfunction in RTT that are represented by defective mitochondrial QC pathways, also providing new potential targets for a therapeutic intervention aimed at slowing down clinical course and manifestations in the affected patients.

Stem Cell-Derived Exosomes in Autism Spectrum Disorder

Neurodevelopmental lifelong pathologies defined by problems with social interaction, communication capacity and presence of repetitive/stereotyped clusters of behavior and interests are grouped under the definition of autism spectrum disorder (ASD). ASD prevalence is still increasing, indicating the need to identify specific biomarkers and novel pharmacotherapies. Neuroinflammation and neuro-immune cross-talk dysregulation are specific hallmarks of ASD, offering the possibility of treating these disorders by stem cell therapy. Indeed, cellular strategies have been postulated, proposed and applied to ASD. However, less is known about the molecular action mechanisms of stem cells. As a possibility, the positive and restorative effects mediated by stem cells could be due to their paracrine activity, by which stem cells produce and release several ameliorative and anti-inflammatory molecules. Among the secreted complex tools, exosomes are sub-organelles, enriched by RNA and proteins, that provide cell-to-cell communication. Exosomes could be the mediators of many stem cell-associated therapeutic activities. This review article describes the potential role of exosomes in alleviating ASD symptoms.

Methyl-CpG Binding Protein 2 in Alzheimer Dementia

Despite decades of research on Alzheimer disease, understanding the complexity of the genetic and molecular interactions involved in its pathogenesis remains far from our grasp. Methyl-CpG Binding Protein 2 (MeCP2) is an important epigenetic regulator enriched in the brain, and recent findings have implicated MeCP2 as a crucial player in Alzheimer disease. Here, we provide comprehensive insights into the pathophysiological roles of MeCP2 in Alzheimer disease. In particular, we focus on how the alteration of MeCP2 expression can impact Alzheimer disease through risk genes, amyloid-β and tau pathology, cell death and neurodegeneration, and cellular senescence. We suggest that Alzheimer disease can be adversely affected by upregulated MeCP2-dependent repression of risk genes (MEF2C, ADAM10, and PM20D1), increased tau accumulation, and neurodegeneration through neuronal cell death (excitotoxicity and apoptosis). In addition, we propose that the progression of Alzheimer disease could be caused by reduced MeCP2-mediated enhancement of astrocytic and microglial senescence and consequent glial SASP (senescence-associated secretory phenotype)-dependent neuroinflammation. We surmise that any imbalance in MeCP2 function would accelerate or cause Alzheimer disease pathogenesis, implying that MeCP2 may be a potential drug target for the treatment and prevention of Alzheimer disease.

Senescence Phenomena and Metabolic Alteration in Mesenchymal Stromal Cells from a Mouse Model of Rett Syndrome

Chromatin modifiers play a crucial role in maintaining cell identity through modulation of gene expression patterns. Their deregulation can have profound effects on cell fate and functions. Among epigenetic regulators, the MECP2 protein is particularly attractive. Mutations in the Mecp2 gene are responsible for more than 90% of cases of Rett syndrome (RTT), a progressive neurodevelopmental disorder. As a chromatin modulator, MECP2 can have a key role in the government of stem cell biology. Previously, we showed that deregulated MECP2 expression triggers senescence in mesenchymal stromal cells (MSCs) from (RTT) patients. Over the last few decades, it has emerged that senescent cells show alterations in the metabolic state. Metabolic changes related to stem cell senescence are particularly detrimental, since they contribute to the exhaustion of stem cell compartments, which in turn determine the falling in tissue renewal and functionality. Herein, we dissect the role of impaired MECP2 function in triggering senescence along with other senescence-related aspects, such as metabolism, in MSCs from a mouse model of RTT. We found that MECP2 deficiencies lead to senescence and impaired mitochondrial energy production. Our results support the idea that an alteration in mitochondria metabolic functions could play an important role in the pathogenesis of RTT.

Neural stem cells from a mouse model of Rett syndrome are prone to senescence, show reduced capacity to cope with genotoxic stress, and are impaired in the differentiation process

Several aspects of stem cell life are governed by epigenetic variations, such as DNA methylation, histone modifications, and chromatin remodeling. Epigenetic events are also connected with the impairment of stem cell functions. For example, during senescence, there are significant changes in chromatin organization that alter transcription. The MECP2 protein can bind methylated cytosines and contribute to regulating gene expression at one of the highest hierarchical levels. Researchers are particularly interested in this protein, as up to 90% of Rett syndrome patients have an MECP2 gene mutation. Nevertheless, the role of MECP2 in this disease remains poorly understood. We used a mouse model of Rett syndrome to evaluate whether residual MECP2 activity in neural stem cells (NSCs) induced the senescence phenomena that could affect stem cell function. Our study clearly demonstrated that the reduced expression of MECP2 is connected with an increase in senescence, an impairment in proliferation capacity, and an accumulation of unrepaired DNA foci. Mecp2^+/− NSCs did not cope with genotoxic stress in the same way as the control cells did. Indeed, after treatment with different DNA-damaging agents, the NSCs from mice with mutated Mecp2 accumulated more DNA damage foci (γ-H2AX+) and were more prone to cell death than the controls. Senescence in Mecp2^+/− NSCs decreased the number of stem cells and progenitors and gave rise to a high percentage of cells that expressed neither stem/progenitor nor differentiation markers. These cells could be senescent and dysfunctional.

In Rett syndrome, neural stem cells lose some of their “stem cell like” properties, impairing brain functions. Patients with this rare neurological condition, almost exclusively girls, show impaired movement and speech beginning at 6–18 months of age. Mutations in the MECP2 gene are known to be involved, but the specifics are poorly understood. Umberto Galderisi at Temple University in Philadelphia and co-workers in Italy used a mouse model to trace how MECP2 mutations affect neural stem cells. They found that the mutated cells lost key stem cell abilities, including the capacity to renew themselves by dividing, and the ability to differentiate, or turn into other cell types. The cells were also highly susceptible to DNA damage and unable to repair it. These results improve our understanding of Rett syndrome and may help develop new treatments.

Endometritis and In Vitro PGE2 Challenge Modify Properties of Cattle Endometrial Mesenchymal Stem Cells and Their Transcriptomic Profile

Mesenchymal stem cells (MSCs) were isolated and characterized from postpartum bovine endometrium of animals with subclinical (n = 5) and clinical endometritis (n = 3) and healthy puerperal females (n = 5). Cells isolated displayed mean morphological features of MSCs and underwent osteogenic, chondrogenic, and adipogenic differentiation after induction (healthy and subclinical). Cells from cows with clinical endometritis did not undergo adipogenic differentiation. All cells expressed mRNAs for selected MSC markers. Endometrial MSCs were challenged in vitro with PGE₂ at concentrations of 0, 1, 3, and 10 μM, and their global transcriptomic profile was studied. Overall, 1127 genes were differentially expressed between unchallenged cells and cells treated with PGE₂ at all concentrations (763 up- and 364 downregulated, fold change > 2, and P < 0.05). The pathways affected the most by the PGE₂ challenge were immune response, angiogenesis, and cell proliferation. In conclusion, we demonstrated that healthy puerperal bovine endometrium contains MSCs and that endometritis modifies and limits some functional characteristics of these cells, such as their ability to proceed to adipogenic differentiation. Also, PGE₂, an inflammatory mediator of endometritis, modifies the transcriptomic profile of endometrial MSCs. A similar situation may occur during inflammation associated with endometritis, therefore affecting the main properties of endometrial MSCs.

Differential mesengenic potential and expression of stem cell-fate modulators in mesenchymal stromal cells from human-term placenta and bone marrow

Placenta has attracted increasing attention over the past decade as a stem cell source for regenerative medicine. In particular, the amniochorionic membrane has been shown to harbor populations of mesenchymal stromal cells (MSCs). In this study, we have characterized ex vivo expanded MSCs from the human amniotic (hAMSCs) and chorionic (hCMSCs) membranes of human full-term placentas and adult bone marrow (hBMSCs). Our results show that hAMSCs, hCMSCs, and hBMSCs express typical mesenchymal (CD73, CD90, CD105, CD44, CD146, CD166) and pluripotent (Oct-4, Sox2, Nanog, Lin28, and Klf4) markers but not hematopoietic markers (CD45, CD34). Ex vivo expanded hAMSCs were found to be of fetal origin, while hCMSCs cultures contained only maternal cells. Cell proliferation was significantly higher in hCMSCs, compared to hAMSCs and hBMSCs. Integrin profiling revealed marked differences in the expression of α subunits between the three cell sources. Cadherin receptors were consistently expressed on a subset of progenitors (ranging from 1% to 60%), while N-CAM (CD56) was only expressed in hAMSCs and hCMSCs but not in hBMSCs. When induced to differentiate, hAMSCs and hCMSCs displayed strong chondrogenic and osteogenic differentiation potential but very limited capacity for adipogenic conversion. In contrast, hBMSCs showed strong differentiation potential along the three lineages. These results illustrate how MSCs from different ontological sources display differential expression of cell-fate mediators and mesodermal differentiation capacity.

Novel insights in basic and applied stem cell therapy

The achievement of novel findings in stem cell research were the subject of the meeting organized by Stem Cell Research Italy (SCR Italy) and by the International Society for Cellular Therapy-Europe (ISCT). Stem cell therapy represents great promise for the future of molecular and regenerative medicine. The use of several types of stem cells is a real opportunity to provide a valid approach to curing several untreatable human diseases. Before it is suitable for clinical applications, stem cell biology needs to be investigated further and in greater detail. Basic stem cell research could provide exact knowledge regarding stem cell action mechanisms, and pre-clinical research on stem cells on an in vivo model of disease provides scientific evidence for future human applications. Applied stem cell research is a promising new approach to handling several diseases. Along with tissue engineering, it offers a new and promising discipline that can help to manage human pathologies through stem cell therapy. All of these themes were discussed in this meeting, covering stem cell subtypes with their newest basic and applied research.

Reduced expression of MECP2 affects cell commitment and maintenance in neurons by triggering senescence: new perspective for Rett syndrome

The neural differentiation process is studied in mesenchymal stem cells obtained from Rett patients and in neuroblastoma cells carrying a partially silenced MECP2 gene. The data suggest that neural cell fate and neuronal maintenance might be perturbed by senescence triggered by impaired MECP2 protein activity either before or after neural differentiation.

MECP2 protein binds preferentially to methylated CpGs and regulates gene expression by causing changes in chromatin structure. The mechanism by which impaired MECP2 activity can induce pathological abnormalities in the nervous system of patients with Rett syndrome (RTT) is not clearly understood. To gain further insight into the role of MECP2 in human neurogenesis, we compared the neural differentiation process in mesenchymal stem cells (MSCs) obtained from a RTT patient and from healthy donors. We further analyzed neural differentiation in a human neuroblastoma cell line carrying a partially silenced MECP2 gene. Senescence and reduced expression of neural markers were observed in proliferating and differentiating MSCs from the RTT patient, which suggests that impaired activity of MECP2 protein may impair neural differentiation, as observed in RTT patients. Next, we used an inducible expression system to silence MECP2 in neuroblastoma cells before and after the induction of neural differentiation via retinoic acid treatment. This approach was used to test whether MECP2 inactivation affected the cell fate of neural progenitors and/or neuronal differentiation and maintenance. Overall, our data suggest that neural cell fate and neuronal maintenance may be perturbed by senescence triggered by impaired MECP2 activity either before or after neural differentiation.

F2-dihomo-isoprostanes as potential early biomarkers of lipid oxidative damage in Rett syndrome

Oxidative damage has been reported in Rett syndrome (RTT), a pervasive developmental disorder caused in up to 95% of cases by mutations in the X-linked methyl-CpG binding protein 2 gene. Herein, we have synthesized F(2)-dihomo-isoprostanes (F(2)-dihomo-IsoPs), peroxidation products from adrenic acid (22:4 n-6), a known component of myelin, and tested the potential value of F(2)-dihomo-IsoPs as a novel disease marker and its relationship with clinical presentation and disease progression. F(2)-dihomo-IsoPs were determined by gas chromatography/negative-ion chemical ionization tandem mass spectrometry. Newly synthesized F(2)-dihomo-IsoP isomers [ent-7(RS)-F(2t)-dihomo-IsoP and 17-F(2t)-dihomo-IsoP] were used as reference standards. The measured ions were the product ions at m/z 327 derived from the [M-181](-) precursor ions (m/z 597) produced from both the derivatized ent-7(RS)-F(2t)-dihomo-IsoP and 17-F(2t)-dihomo-IsoP. Average plasma F(2)-dihomo-IsoP levels in RTT were about one order of magnitude higher than those in healthy controls, being higher in typical RTT as compared with RTT variants, with a remarkable increase of about two orders of magnitude in patients at the earliest stage of the disease followed by a steady decrease during the natural clinical progression. hese data indicate for the first time that quantification of F(2)-dihomo-IsoPs in plasma represents an early marker of the disease and may provide a better understanding of the pathogenic mechanisms behind the neurological regression in patients with RTT.

A comprehensive characterization study of human bone marrow mscs with an emphasis on molecular and ultrastructural properties

Human bone marrow-derived mesenchymal stem cells (hBM-MSCs) continue to draw attention of researchers in the fields of basic science and medicine due to their indispensible regenerative, reparative, angiogenic, anti-apoptotic, and immunosuppressive properties, all of which collectively point out their enormous therapeutic potential. There is still, however, a need for further investigation of their characteristics to broaden their field of use and learn much more about how to control their fate and improve their therapeutic effectiveness. hBM-MSCs were extensively characterized in terms of their growth characteristics, genetic stability, and differentiation capability to the mesodermal and ectodermal cell lineages; a special emphasis was given to their phenotypic and ultrastructural properties. Expression of embryonic stem cell markers Oct4, Rex-1, FoxD-3, Sox2, and Nanog was shown with real-time PCR. Transmission electron microscopy revealed the ultrastructural characteristics of hBM-MSCs; they had pale, irregularly shaped and large euchromatic nuclei, and two distinct areas in their cytoplasm: an intensely stained inner zone rich in mitochondria and rough endoplasmic reticulum (rER) with dilated cisternae and a relatively peripheral zone poor in organelles. hBM-MSCs expressed adipogenic (adipophilin and PPARγ), myogenic (desmin, myogenin, α-SMA), neurogenic (γ-enolase, MAP2a,b, c-fos, nestin, NF-H, NF-L, GFAP, β3-tubulin), osteogenic (osteonectin, osteocalcin, osteopontin, Runx-2, type I collagen), and chondrogenic (type II collagen, SOX9) markers either at RNA or protein level even under basal conditions, without any stimulation towards differentiation. The differentiation potential of hBM-MSCs to adipogenic, osteogenic, and neurogenic lineages was shown by using the relevant differentiation factors.

Intra-brain microinjection of human mesenchymal stem cells decreases allodynia in neuropathic mice

Neuropathic pain is a very complex disease, involving several molecular pathways. Current available drugs are usually not acting on the several mechanisms underlying the generation and propagation of pain. We used spared nerve injury model of neuropathic pain to assess the possible use of human mesenchymal stem cells (hMSCs) as anti-neuropathic tool. Human MSCs were transplanted in the mouse lateral cerebral ventricle. Stem cells injection was performed 4 days after sciatic nerve surgery. Neuropathic mice were monitored 7, 10, 14, 17, and 21 days after surgery. hMSCs were able to reduce pain-like behaviors, such as mechanical allodynia and thermal hyperalgesia, once transplanted in cerebral ventricle. Anti-nociceptive effect was detectable from day 10 after surgery (6 days post cell injection). Human MSCs reduced the mRNA levels of the pro-inflammatory interleukin IL-1beta mouse gene, as well as the neural beta-galactosidase over-activation in prefrontal cortex of SNI mice. Transplanted hMSCs were able to reduce astrocytic and microglial cell activation.

In vitro senescence of rat mesenchymal stem cells is accompanied by downregulation of stemness-related and DNA damage repair genes

Mesenchymal stem cells (MSCs) are of particular interest because they are being tested using cell and gene therapies for a number of human diseases. MSCs represent a rare population in tissues. Therefore, it is essential to grow MSCs in vitro before putting them into therapeutic use. This is compromised by senescence, limiting the proliferative capacity of MSCs. We analyzed the in vitro senescence of rat MSCs, because this animal is a widespread model for preclinical cell therapy studies. After initial expansion, MSCs showed an increased growth doubling time, lost telomerase activity, and expressed senescence-associated beta-galactosidase. Senescence was accompanied by downregulation of several genes involved in stem cell self-renewal. Of interest, several genes involved in DNA repair also showed a significant downregulation. Entry into senescence occurred with characteristic changes in Retinoblastoma (RB) expression patterns. Rb1 and p107 genes expression decreased during in vitro cultivation. In contrast, pRb2/p130 became the prominent RB protein. This suggests that RB2/P130 could be a marker of senescence or that it even plays a role in triggering the process in MSCs.

Characterization of Gaucher disease bone marrow mesenchymal stromal cells reveals an altered inflammatory secretome

Gaucher disease causes pathologic skeletal changes that are not fully explained. Considering the important role of mesenchymal stromal cells (MSCs) in bone structural development and maintenance, we analyzed the cellular biochemistry of MSCs from an adult patient with Gaucher disease type 1 (N370S/L444P mutations). Gaucher MSCs possessed a low glucocerebrosidase activity and consequently had a 3-fold increase in cellular glucosylceramide. Gaucher MSCs have a typical MSC marker phenotype, normal osteocytic and adipocytic differentiation, growth, exogenous lactosylceramide trafficking, cholesterol content, lysosomal morphology, and total lysosomal content, and a marked increase in COX-2, prostaglandin E2, interleukin-8, and CCL2 production compared with normal controls. Transcriptome analysis on normal MSCs treated with the glucocerebrosidase inhibitor conduritol B epoxide showed an up-regulation of an array of inflammatory mediators, including CCL2, and other differentially regulated pathways. These cells also showed a decrease in sphingosine-1-phosphate. In conclusion, Gaucher disease MSCs display an altered secretome that could contribute to skeletal disease and immune disease manifestations in a manner distinct and additive to Gaucher macrophages themselves.

Controversial issue: is it safe to employ mesenchymal stem cells in cell-based therapies?

The prospective clinical use of multipotent mesenchymal stromal stem cells (MSC) holds enormous promise for the treatment of a large number of degenerative and age-related diseases. However, the challenges and risks for cell-based therapies are multifaceted. The risks for patients receiving stem cells, which have been expanded in vitro in the presence of xenogenic compounds, can hardly be anticipated and methods for the culture and manipulation of "safe" MSC ex vivo are being investigated. During in vitro expansion, stem cells experience a long replicative history and are thus subject to damage from intracellular and extracellular influences. While murine MSC are prone to cellular transformation in culture, human MSC do not transform. One reason for this striking difference is that during long-term culture, human MSC finally become replicatively senescent. In consequence, this greatly restricts their proliferation and differentiation efficiency. It however also limits the yield of sufficient numbers of cells needed for therapy. Another issue is to eliminate contamination of expanding cells with serum-bound pathogenic agents in order to reduce the risks for infection. A recent technical advancement, which applies human serum platelet lysates as an alternative source for growth factors and essential supplements, allows the unimpaired proliferation of MSC in the absence of animal sera. Here, we present an update regarding cellular senescence of MSC and recent insights concerning potential risks associated with their clinical use.