Research Projects

Gene Editing and Gene Replacement for Muscular Dystrophy

Over 400 different genes have been shown to be causal for different neuromuscular disorders, and the majority of these diseases will benefit from gene replacement and/or gene editing approaches. A main issue faced by the field is the ability to deliver these platforms to the proper site and with sufficient efficiency. The Spencer lab is developing AAV based gene replacement approaches for limb girdle muscular dystrophy as well as gene editing platforms for Duchenne. To deliver these therapies we are using AAV capsid engineering approaches to optimize the delivery to muscle stem cells.

Restoration of dystrophin protein in humanized mdx mice. Green shows dystrophin at the membrane of dystrophic muscles.
A table comparing dystrophin protein levels in treated and untreated humanized mdx mice. The top half shows dystrophin levels in the heart, and the bottom half shows dystrophin levels in the diaphragm. Dystrophin at the membrane of dystrophic muscles is indicated by fluorescent green. There is noticeably more fluorescent green in the heart and diaphragm of treated mice, suggesting restoration of dystrophin in these muscles after treatment.

Immune response to AAV vectors

AAV-based therapies induce an immune response against the viral vector and thus are limited to single dosing. We have initiated a program to study these immune responses and are using both mouse models and human samples from our Muscular Dystrophy clinic. By understanding how the immune system interfaces with AAV, we can develop strategies to overcome immune reactions and possibly re-dose. The immune response is also responsible for unwanted serious adverse events in patients dosed with high levels of AAV, so our laboratory is actively assessing ways to reduce these unwanted side effects.

Single cell sequencing UMAP plot of peripheral blood mononuclear cells isolated from Duchenne muscular dystrophy subjects prior to (pre) and after (post) administration of an AAV-based gene therapy
A single-cell sequencing Uniform Manifold Approximation and Projection (UMAP) plot comparing peripheral blood mononuclear cells in Duchenne patients before and after dosing with AAV-minidystrophin. Each dot represents a single cell and is colored according to cell type. Interestingly, the plot does not show a perceptible difference pre- and post-treatment.

Pathogenesis and Therapies for Duchenne and limb girdle muscular dystrophy

The Spencer has been interested in understanding the pathogenesis of and developing therapies for limb girdle muscular dystrophies (LGMD), particularly for LGMDR1/2A. LGMDR1/2A is the most prevalent form of the LGMDs but is one of the most complicated to understand. We showed that muscles with mutations in CAPN3 do not respond to loading cues to activate calcium calmodulin kinase, which is necessary to turn on genes involved in muscle remodeling and induction of the slow oxidative program of gene expression. We identified the first therapeutic compound to treat LGMDR1/2A, that is now being optimized through medicinal chemistry efforts

The Spencer lab identified a small molecule called AMBMP that enhances the slow oxidative program in skeletal muscle. In collaboration with the Varghese lab in Neurology, the investigators are optimizing this compound to be used in patients with muscular dystrophy.
The Spencer lab has identified a small molecule called AMBMP that enhances the slow oxidative program in skeletal muscle and is working with the Varghese lab to optimize its use in treating patients with muscular dystrophy. This three-column table compares the slow oxidative program in muscles of healthy wild-type mice, Calpain-3 knock-out mice, and Calpain-3 knock-out mice treated with AMBMP. The left column shows that, in healthy wild-type mice, exercise induces calcium calmodulin kinase activation and expression of slow oxidative genes. The middle column shows that, in Calpain-3 knock-out mice, this signaling is blunted, leading to minimal induction of slow oxidative genes. Finally, the right column shows that AMBMP can mimic the effect of exercise, inducing calcium calmodulin kinase activation and expression of slow oxidative genes in Calpain-3 knock-out mice.