A Perturbed MicroRNA Expression Pattern Characterizes Embryonic Neural Stem Cells Derived from a Severe Mouse Model of Spinal Muscular Atrophy (SMA).

Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder and the leading genetic cause of death in infants. Despite the disease-causing gene, survival motor neuron (SMN1), encodes a ubiquitous protein, SMN1 deficiency preferentially affects spinal motor neurons (MNs), leaving the basis of this selective cell damage still unexplained. As neural stem cells (NSCs) are multipotent self-renewing cells that can differentiate into neurons, they represent an in vitro model for elucidating the pathogenetic mechanism of neurodegenerative diseases such as SMA. Here we characterize for the first time neural stem cells (NSCs) derived from embryonic spinal cords of a severe SMNΔ7 SMA mouse model. SMNΔ7 NSCs behave as their wild type (WT) counterparts, when we consider neurosphere formation ability and the expression levels of specific regional and self-renewal markers. However, they show a perturbed cell cycle phase distribution and an increased proliferation rate compared to wild type cells. Moreover, SMNΔ7 NSCs are characterized by the differential expression of a limited number of miRNAs, among which miR-335-5p and miR-100-5p, reduced in SMNΔ7 NSCs compared to WT cells. We suggest that such miRNAs may be related to the proliferation differences characterizing SMNΔ7 NSCs, and may be potentially involved in the molecular mechanisms of SMA.

IPLEX administration improves motor neuron survival and ameliorates motor functions in a severe mouse model of spinal muscular atrophy.

Spinal muscular atrophy (SMA) is an inherited neurodegenerative disorder and the first genetic cause of death in childhood. SMA is caused by low levels of survival motor neuron (SMN) protein that induce selective loss of α-motor neurons (MNs) in the spinal cord, resulting in progressive muscle atrophy and consequent respiratory failure. To date, no effective treatment is available to counteract the course of the disease. Among the different therapeutic strategies with potential clinical applications, the evaluation of trophic and/or protective agents able to antagonize MNs degeneration represents an attractive opportunity to develop valid therapies. Here we investigated the effects of IPLEX (recombinant human insulinlike growth factor 1 [rhIGF-1] complexed with recombinant human IGF-1 binding protein 3 [rhIGFBP-3]) on a severe mouse model of SMA. Interestingly, molecular and biochemical analyses of IGF-1 carried out in SMA mice before drug administration revealed marked reductions of IGF-1 circulating levels and hepatic mRNA expression. In this study, we found that perinatal administration of IPLEX, even if does not influence survival and body weight of mice, results in reduced degeneration of MNs, increased muscle fiber size and in amelioration of motor functions in SMA mice. Additionally, we show that phenotypic changes observed are not SMN-dependent, since no significant SMN modification was addressed in treated mice. Collectively, our data indicate IPLEX as a good therapeutic candidate to hinder the progression of the neurodegenerative process in SMA.

Small Fragment Homologous Replacement (SFHR): sequence-specific modification of genomic DNA in eukaryotic cells by small DNA fragments.

The sequence-specific correction of a mutated gene (e.g., point mutation) by the Small Fragment Homologous Replacement (SFHR) method is a highly attractive approach for gene therapy. Small DNA fragments (SDFs) were used in SFHR to modify endogenous genomic DNA in both human and murine cells. The advantage of this gene targeting approach is to maintain the physiologic expression pattern of targeted genes without altering the regulatory sequences (e.g., promoter, enhancer), but the application of this technique requires the knowledge of the sequence to be targeted. In our recent study, an optimized SFHR protocol was used to replace the eGFP mutant sequence in SV-40-transformed mouse embryonic fibroblast (MEF-SV40), with the wild-type eGFP sequence. Nevertheless in the past, SFHR has been used to correct several mutant genes, each related to a specific genetic disease (e.g., spinal muscular atrophy, cystic fibrosis, severe combined immune deficiency). Several parameters can be modified to optimize the gene modification efficiency, as described in our recent study. In this chapter we describe the main guidelines that should be followed in SFHR application, in order to increase technique efficiency.

Small fragment homologous replacement: evaluation of factors influencing modification efficiency in an eukaryotic assay system.

Homologous Replacement is used to modify specific gene sequences of chromosomal DNA in a process referred to as "Small Fragment Homologous Replacement", where DNA fragments replace genomic target resulting in specific sequence changes. To optimize the efficiency of this process, we developed a reporter based assay system where the replacement frequency is quantified by cytofluorimetric analysis following restoration of a stably integrated mutated eGFP gene in the genome of SV-40 immortalized mouse embryonic fibroblasts (MEF-SV-40). To obtain the highest correction frequency with this system, several parameters were considered: fragment synthesis and concentration, cell cycle phase and methylation status of both fragment and recipient genome. In addition, different drugs were employed to test their ability to improve technique efficiency. SFHR-mediated genomic modification resulted to be stably transmitted for several cell generations and confirmed at transcript and genomic levels. Modification efficiency was estimated in a range of 0.01-0.5%, further increasing when PARP-1 repair pathway was inhibited. In this study, for the first time SFHR efficiency issue was systematically approached and in part addressed, therefore opening new potential therapeutic ex-vivo applications.

Bone marrow and umbilical cord blood human mesenchymal stem cells: state of the art.

Mesenchymal stem cells (MSCs) are multipotent adult stem cells present in all tissues, as part of the perivascular population. As multipotent cells, MSCs can differentiate into different tissues originating from mesoderm ranging from bone and cartilage, to cardiac muscle. MSCs are an excellent candidate for cell therapy because they are easily accessible, their isolation is straightforward, they can be bio-preserved with minimal loss of potency, and they have shown no adverse reactions to allogeneic versus autologous MSCs transplants. Therefore, MSCs are being explored to regenerate damaged tissue and treat inflammation, resulting from cardiovascular disease and myo-cardial infarction (MI), brain and spinal cord injury, stroke, diabetes, cartilage and bone injury, Crohn's disease and graft versus host disease (GvHD). Most of the application and clinical trials involve MSCs from bone marrow (BMMSCs). Transplantation of MSCs from bone marrow is considered safe and has been widely tested in clinical trials of cardiovascular, neurological, and immunological disease with encouraging results. There are examples of MSCs utilization in the repair of kidney, muscle and lung. The cells were also found to promote angiogenesis, and were used in chronic skin wound treatment. Recent studies involve also mesenchymal stem cell transplant from umbilical cord (UCMSCt). One of these demonstrate that UCMSCt may improve symptoms and biochemical values in patients with severe refractory systemic lupus erythematosus (SLE), and therefore this source of MSCs need deeper studies and require more attention. However, also if there are 79 registered clinical trial sites for evaluating MSC therapy throughout the world, it is still a long way to go before using these cells as a routinely applied therapy in clinics.