Systemic, postsymptomatic antisense oligonucleotide rescues motor unit maturation delay in a new mouse model for type II/III spinal muscular atrophy.

Clinical presentation of spinal muscular atrophy (SMA) ranges from a neonatal-onset, very severe disease to an adult-onset, milder form. SMA is caused by the mutation of the Survival Motor Neuron 1 (SMN1) gene, and prognosis inversely correlates with the number of copies of the SMN2 gene, a human-specific homolog of SMN1. Despite progress in identifying potential therapies for the treatment of SMA, many questions remain including how late after onset treatments can still be effective and what the target tissues should be. These questions can be addressed in part with preclinical animal models; however, modeling the array of SMA severities in the mouse, which lacks SMN2, has proven challenging. We created a new mouse model for the intermediate forms of SMA presenting with a delay in neuromuscular junction maturation and a decrease in the number of functional motor units, all relevant to the clinical presentation of the disease. Using this new model, in combination with clinical electrophysiology methods, we found that administering systemically SMN-restoring antisense oligonucleotides (ASOs) at the age of onset can extend survival and rescue the neurological phenotypes. Furthermore, these effects were also achieved by administration of the ASOs late after onset, independent of the restoration of SMN in the spinal cord. Thus, by adding to the limited repertoire of existing mouse models for type II/III SMA, we demonstrate that ASO therapy can be effective even when administered after onset of the neurological symptoms, in young adult mice, and without being delivered into the central nervous system.

Survival motor neuron protein in motor neurons determines synaptic integrity in spinal muscular atrophy.

The inherited motor neuron disease spinal muscular atrophy (SMA) is caused by deficient expression of survival motor neuron (SMN) protein and results in severe muscle weakness. In SMA mice, synaptic dysfunction of both neuromuscular junctions (NMJs) and central sensorimotor synapses precedes motor neuron cell death. To address whether this synaptic dysfunction is due to SMN deficiency in motor neurons, muscle, or both, we generated three lines of conditional SMA mice with tissue-specific increases in SMN expression. All three lines of mice showed increased survival, weights, and improved motor behavior. While increased SMN expression in motor neurons prevented synaptic dysfunction at the NMJ and restored motor neuron somal synapses, increased SMN expression in muscle did not affect synaptic function although it did improve myofiber size. Together these data indicate that both peripheral and central synaptic integrity are dependent on motor neurons in SMA, but SMN may have variable roles in the maintenance of these different synapses. At the NMJ, it functions at the presynaptic terminal in a cell-autonomous fashion, but may be necessary for retrograde trophic signaling to presynaptic inputs onto motor neurons. Importantly, SMN also appears to function in muscle growth and/or maintenance independent of motor neurons. Our data suggest that SMN plays distinct roles in muscle, NMJs, and motor neuron somal synapses and that restored function of SMN at all three sites will be necessary for full recovery of muscle power.

Cellular expression requirements for inhibition of type 1 diabetes by a dominantly protective major histocompatibility complex haplotype.

The H2(g7) (K(d), A(g7), E(null), and D(b)) major histocompatibility complex (MHC) is the primary genetic contributor to type 1 diabetes in NOD mice. NOD stocks congenically expressing other MHC haplotypes such as H2(nb1) (K(b), A(nb1), E(k), and D(b)) in a heterozygous state are type 1 diabetes resistant. Hematopoietically derived antigen-presenting cells (APCs) expressing H2(nb1) MHC molecules delete or inactivate autoreactive diabetogenic T-cells. Thus, provided a relatively benign preconditioning protocol is ultimately developed, hematopoietic chimerization by APCs expressing dominantly protective MHC molecules could conceivably provide a means for type 1 diabetes prevention in humans. Before hematopoietic chimerization can be considered for type 1 diabetes prevention, it must be determined what subtype(s) of APCs (B-cells, macrophages, and/or dendritic cells) expressing protective MHC molecules most efficiently inhibit disease, as well as the engraftment level they must achieve to accomplish this. These issues were addressed through analyses of NOD background bone marrow chimeras in which H2(nb1) molecules were selectively expressed on variable proportions of different APC subtypes. While a modest B-cell effect was observed, the strongest type 1 diabetes protection resulted from at least 50% of dendritic cells and macrophages expressing H2(nb1) molecules. At this engraftment level, H2(nb1)-expressing dendritic cells and macrophages mediated virtually complete deletion of a highly pathogenic CD8 T-cell population.

Optimizing mouse models of neurodegenerative disorders: are therapeutics in sight?

The genomic and biologic conservation between mice and humans, along with our increasing ability to manipulate the mouse genome, places the mouse as a premier model for deciphering disease mechanisms and testing potential new therapies. Despite these advantages, mouse models of neurodegenerative disease are sometimes difficult to generate and can present challenges that must be carefully addressed when used for preclinical studies. For those models that do exist, the standardization and optimization of the models is a critical step in ensuring success in both basic research and preclinical use. This review looks back on the history of model development for neurodegenerative diseases and highlights the key strategies that have been learned in order to improve the design, development and use of mouse models in the study of neurodegenerative disease.

Postsymptomatic restoration of SMN rescues the disease phenotype in a mouse model of severe spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a common neuromuscular disorder in humans. In fact, it is the most frequently inherited cause of infant mortality, being the result of mutations in the survival of motor neuron 1 (SMN1) gene that reduce levels of SMN protein. Restoring levels of SMN protein in individuals with SMA is perceived to be a viable therapeutic option, but the efficacy of such a strategy once symptoms are apparent has not been determined. We have generated mice harboring an inducible Smn rescue allele and used them in a model of SMA to investigate the effects of turning on SMN expression at different time points during the course of the disease. Restoring SMN protein even after disease onset was sufficient to reverse neuromuscular pathology and effect robust rescue of the SMA phenotype. Importantly, our findings also indicated that there was a therapeutic window of opportunity from P4 through P8 defined by the extent of neuromuscular synapse pathology and the ability of motor neurons to respond to SMN induction, following which restoration of the protein to the organism failed to produce therapeutic benefit. Nevertheless, our results suggest that even in severe SMA, timely reinstatement of the SMN protein may halt the progression of the disease and serve as an effective postsymptomatic treatment.

Idd9/11 genetic locus regulates diabetogenic activity of CD4 T-cells in nonobese diabetic (NOD) mice.

OBJECTIVE: Although the H2(g7) major histocompatibility complex (MHC) provides the primary pathogenic component, the development of T-cell-mediated autoimmune type 1 diabetes in NOD mice also requires contributions from other susceptibility (Idd) genes. Despite sharing the H2(g7) MHC, the closely NOD-related NOR strain remains type 1 diabetes resistant because of contributions of protective Idd5.2, Idd9/11, and Idd13 region alleles. To aid their eventual identification, we evaluated cell types in which non-MHC Idd resistance genes in NOR mice exert disease-protective effects. RESEARCH DESIGN AND METHODS: Adoptive transfer and bone marrow chimerism approaches tested the diabetogenic activity of CD4 and CD8 T-cells from NOR mice and NOD stocks congenic for NOR-derived Idd resistance loci. Tetramer staining and mimotope stimulation tested the frequency and proliferative capacity of CD4 BDC2.5-like cells. Regulatory T-cells (Tregs) were identified by Foxp3 staining and functionally assessed by in vitro suppression assays. RESULTS: NOR CD4 T-cells were less diabetogenic than those from NOD mice. The failure of NOR CD4 T-cells to induce type 1 diabetes was not due to decreased proliferative capacity of BDC2.5 clonotypic-like cells. The frequency and function of Tregs in NOD and NOR mice were also equivalent. However, bone marrow chimerism experiments demonstrated that intrinsic factors inhibited the pathogenic activity of NOR CD4 T-cells. The NOR Idd9/11 resistance region on chromosome 4 was found to diminish the diabetogenic activity of CD4 but not CD8 T-cells. CONCLUSIONS: In conclusion, we demonstrated that a gene(s) within the Idd9/11 region regulates the diabetogenic activity of CD4 T-cells.

Through regulation of TCR expression levels, an Idd7 region gene(s) interactively contributes to the impaired thymic deletion of autoreactive diabetogenic CD8+ T cells in nonobese diabetic mice.

When expressed in NOD, but not C57BL/6 (B6) genetic background mice, the common class I variants encoded by the H2g7 MHC haplotype aberrantly lose the ability to mediate the thymic deletion of autoreactive CD8+ T cells contributing to type 1 diabetes (T1D). This indicated some subset of the T1D susceptibility (Idd) genes located outside the MHC of NOD mice interactively impair the negative selection of diabetogenic CD8+ T cells. In this study, using both linkage and congenic strain analyses, we demonstrate contributions from a polymorphic gene(s) in the previously described Idd7 locus on the proximal portion of Chromosome 7 predominantly, but not exclusively, determines the extent to which H2g7 class I molecules can mediate the thymic deletion of diabetogenic CD8+ T cells as illustrated using the AI4 TCR transgenic system. The polymorphic Idd7 region gene(s) appears to control events that respectively result in high vs low expression of the AI4 clonotypic TCR alpha-chain on developing thymocytes in B6.H2g7 and NOD background mice. This expression difference likely lowers levels of the clonotypic AI4 TCR in NOD, but not B6.H2g7 thymocytes, below the threshold presumably necessary to induce a signaling response sufficient to trigger negative selection upon Ag engagement. These findings provide further insight to how susceptibility genes, both within and outside the MHC, may interact to elicit autoreactive T cell responses mediating T1D development in both NOD mice and human patients.

Partial versus full allogeneic hemopoietic chimerization is a preferential means to inhibit type 1 diabetes as the latter induces generalized immunosuppression.

In both humans and NOD mice, particular combinations of MHC genes provide the primary risk factor for development of the autoreactive T cell responses causing type 1 diabetes (T1D). Conversely, other MHC variants can confer dominant T1D resistance, and previous studies in NOD mice have shown their expression on hemopoietically derived APC is sufficient to induce disease protection. Although allogeneic hemopoietic chimerization can clearly provide a means for blocking T1D development, its clinical use for this purpose has been obviated by a requirement to precondition the host with what would be a lethal irradiation dose if bone marrow engraftment is not successful. There have been reports in which T1D-protective allogeneic hemopoietic chimerization was established in NOD mice that were preconditioned by protocols not including a lethal dose of irradiation. In most of these studies, virtually all the hemopoietic cells in the NOD recipients eventually converted to donor type. We now report that a concern about such full allogeneic chimeras is that they are severely immunocompromised potentially because their T cells are positively selected in the thymus by MHC molecules differing from those expressed by the APC available in the periphery to activate T cell effector functions. However, this undesirable side effect of generalized immunosuppression is obviated by a new protocol that establishes without a lethal preconditioning component, a stable state of mixed allogeneic hemopoietic chimerism sufficient to inhibit T1D development and also induce donor-specific tolerance in NOD recipients.

CD38 is required for the peripheral survival of immunotolerogenic CD4+ invariant NK T cells in nonobese diabetic mice.

T cell-mediated autoimmune type-1 diabetes (T1D) in NOD mice partly results from this strain's numerical and functional defects in invariant NK T (iNKT) cells. T1D is inhibited in NOD mice treated with the iNKT cell superagonist alpha-galactosylceramide through a process involving enhanced accumulation of immunotolerogenic dendritic cells in pancreatic lymph nodes. Conversely, T1D is accelerated in NOD mice lacking CD38 molecules that play a role in dendritic cell migration to inflamed tissues. Unlike in standard NOD mice, alpha-galactosylceramide pretreatment did not protect the CD38-deficient stock from T1D induced by an adoptively transferred pancreatic beta cell-autoreactive CD8 T cell clone (AI4). We found that in the absence of CD38, ADP-ribosyltransferase 2 preferentially activates apoptotic deletion of peripheral iNKT cells, especially the CD4+ subset. Therefore, this study documents a previously unrecognized role for CD38 in maintaining survival of an iNKT cell subset that preferentially contributes to the maintenance of immunological tolerance.