Pediatric Neurogenetic Disorders: Diagnosis, Disease Models and Therapeutic Interventions
Biomedical research often focuses on common disorders that affect a significant portion of our population (e.g., diabetes, cancer, heart disease). This approach prudently allocates our limited research funds toward disorders that have the most widespread impact on our collective medical needs. Unfortunately, this path often neglects rare disorders that affect only a handful of patients.
Rare neurogenetic disorders are often caused by a genetic aberration that prohibits the proper functioning of the central or peripheral nervous system (i.e., the brain, spinal cord, muscle and/or peripheral nerves). Because many of the genes involved in these disorders are crucial to neurological development and normal human functioning, the impact of these disorders is often observed early in life. Consequently, pediatric neurogenetic disorders are a major subset of rare disorders, with many being severely debilitating and/or life-threatening.
Research into rare disorders is important because it has potential to help patients afflicted with these disorders while also providing critical insight into cellular physiology and disease mechanisms. This information can subsequently be applied toward understanding other diseases, both common and rare. For example, Brown and Goldstein's work with familial hypercholesterolemia, an uncommon disorder, provided key insights into cholesterol homeostasis that radically altered the treatment of vascular disease. Similar results have been seen with neurogenetic disorders.
The recent emergence of genomic methods such as high-density SNP arrays along with whole exome and genome sequencing has allowed the scientific community to identify pathogenic mutations in genes that would often not be included in the diagnostic workup. Subsequently, with further research, the association of these genes with their pathogenic mechanisms has provided valuable insight into the molecular and cellular function of the nervous system. Likewise, the development of induced pluripotent stem cells (iPSCs) has provided a platform for us to generate patient-specific stem cells that are capable of generating human disease models for these rare disorders. These investigations of disease mechanisms can subsequently have potential for high-throughput drug screening and the development of personalized therapies.
Figure 1. Schematic overview of the Pierson lab's pediatric neurogenetic disorder research. The Pierson lab works with the Cedars-Sinai Pediatric Neurogenetic and Neuromuscular Clinic. The lab uses modern genomic platforms and induced pluripotent stem cell (iPSC) technologies to achieve genetic diagnoses and create cell culture models of these rare disorders, respectively.
Drug-Inducible Gene and Cell Therapy Systems
Gene and cell therapy (GCT) provides an avenue for introducing or augmenting the expression of therapeutic proteins in tissues affected by disease. For example, individuals with neurogenetic diseases may have a specific gene mutated that results in the absence or dysfunction of an important protein leading to disease. Gene expression systems could allow for introduction of a missing gene product and subsequently ameliorate the disease. Likewise, other pathologies may not be associated with one specific genetic abnormality, but disease manifestations may be reduced by the expression of specific therapeutic proteins in the affected tissues (e.g., glial-derived neurotrophic factor (GDNF), insulin-like growth factor 1 (IGF-1), etc.). To date, the majority of research focused on gene therapy systems have been limited by two factors that make these systems less than optimal for therapeutic use in human nervous systems:
- The use of viral expression vectors for in vivo delivery of the gene-of-interest
- The use of constitutively active promoters for expression of therapeutic proteins.
We are investigating the use of a mifepristone-inducible gene expression system that provides control of the expression of a therapeutic gene-of-interest. This system allows us to generate pathologically relevant and tissue-specific cells types (e.g., neural progenitor cells or glia) that have been transduced with a drug-inducible system that can then be transplanted into affected tissues. The presence of this inducible system within transplanted cells allows for control of the expression of therapeutic proteins via administration or withdrawal of mifepristone.
Currently, we are evaluating the efficiency of this system both in vitro and in vivo in a variety of neurologically relevant cell types. We look forward to translating this work into human stem cell-based cellular therapies to provide therapeutic options and potential clinical trials for our patients. We continue to investigate multiple modalities of our system and aim to elucidate the optimal settings and gene “dosages” to provide physiologically relevant expression that can be adjusted for personalized treatment strategies.
Figure 2. Mifepristone (MFP)-inducible expression of target genes. (a) Fluorescence microscopy and (b and c) western blot analysis of target gene expression (dsRED; eGFP) using cells infected with a mifepristone-inducible expression system. (a) Co-expression of two target genes (dsRED; eGFP) with (+) or without (-) mifepristone treatment. (b) Activation and deactivation of target genes in vitro following mifepristone treatment or withdrawal, respectively. (c) MFP concentration-dependant expression of target genes.