DY PATIL BIOTECHNOLOGY AND BIOINFORMATICS INSTITUTE, PUNE
Parkinson’s disease is a progressive disorder of the nervous system which impairs movement. The obvious external symptoms of the disease are well known today – characteristic tremor, stiffness, slowness and/or walking, balance, and coordination problems. However, what people fail to see are the more subtle, less apparent symptoms, such as depression, anxiety, and apathy. The disease itself is so common that it affects around 7 to 10 million people over the world. The age groups of the people who are affected are around 60 to 80 (41 cases per 1,00,000 observed) to more than at least 1900 cases per 1,00,000 observed in the age group above 80. Generally, with an increase in age, the chances of incidence of the disease increase considerably. So, no matter what the age group, a life of hardships, both on mental and physical levels, awaits these people, with no means of curing it after its diagnosis.
Why is Parkinson’s incurable?
Parkinson’s is characterized by the loss of dopaminergic neurons in the Substantia nigra (a basal ganglionic structure present in the midbrain which plays a pivotal role in movement) and thus a severe decrease of dopamine in the striatum. Alpha-synuclein protein clumps and tangles up inside the cranial neurons, forming “Lewy Bodies”. Thus, Lewy Bodies are primarily the products of the phenomenon of protein misfolding. All of this slows down neuronal conductions and ultimately causes neuronal death. This is what we identify as Parkinson’s disease (and Parkinson’s related dementia). Delivery of any corrective gene or chemical to the patient’s nervous system in such conditions proves to be very difficult due to the presence of obstacles created by the blood-brain barrier and several other immunological responses, and thus, as of now, no direct cure has been discovered for the neurodegenerative disorder.
HSPs in Viral Vectors – To the Rescue!
The ubiquitination and degradation of several proteins are facilitated by HSPs (heat shock proteins). Various types of HSPs and HSCs (heat shock cognates) and other co-chaperones (differing on the genus, family, or even species level) ensure that the misfolded proteins are maintained in a degradation-competent state and optimize their direction to degradation machinery. In Parkinson’s disease, decreased proteasome activity is ensured by HSP’s, by virtue of them acting as protein folding chaperones.
Hence, AAVs (Adeno Associated Viruses) could be used as viral vectors to deliver, organically induce, and overexpress molecular chaperone proteins such as heat shock cognates (HSCs) or short HSP (heat shock proteins) genes in cell lines and ultimately into organisms. They can be used to selectively protect dopaminergic neurons from degradation, and thus successfully curtail the formation and spread of Lewy Bodies in the Substantia nigra. (Inspired by the studies conducted by Shinichi Muramatsu, K. Ozawa, et al)
Reason for Choice of Associated Adenoviral vectors
AAVs belong to the genus Dependoparvovirus, and the family Parvoviridiae. AAV is not known to cause disease. The virus causes a very mild immune response, and exhibits a proven and tested lack of pathogenicity, thus managing to create a bio ethically sound approach. Recently, clinical trials for retinal ganglionic cells using AAVs, in human models as well as in Mus musculus (mouse) and Rattus rattus (rat) models have thus shown great promise for its successful, non-immunogenic integration into the host. As a result, AAVs have been chosen as the standard viral vectors in human trials in retina-based research as well!
Experiments conducted by Lowery et al illustrate the methods which can be used to accomplish this task. These are intravitreal injections of the above-mentioned genes, intracranial injection of AAV vector (using stereotaxic coordinates, a micropipette and for precise delivery of AAV to the desired area, an automated pump may be used to ensure minimal damage to the surrounding tissue). For individual experiments, the injection parameters can be tailored accordingly, in the sense that we can review the subject age at the time of injection, mode of injection, location of injection, its volume, and the rate at specific and variable times, ensuring optimization of the AAV serotype and the strength of promoters thus involved to enhance gene expression.
Potential Cure for Parkinson’s
While achieving successful overexpression of HSPs into cell lines, (and further into organisms), through the chosen AAV vector, of course, one of the imperatives is avoiding genetic damage to the host genome through the viral vector in all generations of cell lines (and in chosen organisms subsequently).
This project will have significance in curing Parkinson’s disease, by not only curtailing the spread of Lewy Bodies but also permanently reducing the expression and slowing down the effect of neurodegeneration. The impacts this area of research could have are potentially endless! Its significance would be inducing of HSCs or even other HSP-60, HSP-70 genes and then ensuring their integration into a cell line, and their successful integration into the metabolic pathways of model organisms, and ultimately into humans.