CNS Disorders is a broad term which includes several neurodegenerative and neurological disorders such as Alzheimer’s disease (AD), Cerebral Palsy, Parkinson’s (PD), Batten’s disease, Huntington’s (HD), ALS and so on. As we move forward with stem cells research in therapy for such neurological disorders, it’s observed that the treatment shows promise. The stem cells migrate to the damaged areas and assume the function of the neurons 1.
PD causes degeneration of dopaminergic nigrostriatal pathway and also a loss in motor control, but it also causes several non-motor problems to arise. HD is autosomal dominant disease which can cause cellular dysfunction with loss of numerous central nervous system sites. ALS causes dysfunction and degeneration of motor neurons in spinal cord, cerebral cortex and brainstem, causing muscle weakness and death within weeks. Cerebral Palsy on the other hand is caused during birth which causes several complications such as seizures, blindness, and so on. Lastly; AD, is a complex and fatal disorder which progressively destroys the brain cells controlling memory, thought and language 2.
As the aging population is increasing, the probability of acquiring a neurological or neurodegenerative disorder is also increasing 3. CNS disorders are said to affect at least 1.5 million people worldwide and are results of 1% deaths. One of the major reasons a drug or therapy has not worked on such disorders is due to the presence of Blood-Brain Barrier (BBB) along with a Blood-Cerebrospinal Fluid Barrier (BCFB) 4.
The increase in research on therapies for such diseases is due to the fact that it’s difficult to cross the blood-brain barrier. Conventional therapies, although effective are not the optimum therapies. The therapies which are still under development are nanotechnology and stem cell therapy, both of which have shown some promising results 5.
Neurodegenerative disorders though found commonly, a cause for such is not yet found. It has been seen though, that a person with a family history of one can later be diagnosed with it. Such disorders can affect an infant at an early stage so as to reduce the complete damage. If not diagnosed accurately, these can affect their lifestyle throughout their life 6.
Another problem is due to the fact that the components of CNS; i.e., the brain, the spinal cord, and the retina have a limited capacity to regenerate. This creates a critical need for therapies which help in regeneration of cells is such disorders. The complexity of the whole CNS network makes it more difficult to find a successful regenerative therapy 7.
Stem cells are the unspecialized cells found throughout the body which can regenerate any damaged area due to their ability to differentiate themselves into specialized cells. Their multipotency and proliferative capacity make them a highly important tool to use as a therapy in neurodegenerative disorders. Although many of the researchers have shown stem cells to be a viable option through numerous animal clinical trials for therapy, they are still controversial to use in humans 8.
The two main types of stem cells are Embryonic Stem Cells & Adult Stem Cells (Fig1.1). Embryonic stem cells are obtained from the inner mass of blastula and are easy to culture in lab but have also shown some safety issues. They need to be therefore investigated more before they can be used in human clinical trials. Among the Adult stem cells; Adult Neural Precursor Cells and Bone Marrow Cells show better promises.
The most extensive work so far from the CNS perspective is done on Embryonic Neural Stem Cells; derived from neuroepithelium of a developing embryo. They do have complications due to being very difficult to harvest and also culturing these cells give a mixed population of progenitor and stem cells 9.
Over the decades now, stem cell therapy has shown some promises; clinical fetal tissue transplants have shown that dopaminergic neurons can survive longer which can be really beneficial to patients with Parkinson’s. Advancements were made so as to culture neurons as well as dopaminergic neurons in large amounts. Despite the promises shown by such examples, further study is required to culture neural cells from other tissues and also to check the functioning of the cultured cells 10.
Recent developments in stem cell therapy have contributed significantly to our understanding of brain development and maintenance. In the last five decades, the overall strategy has been to treat the symptoms whilst offering the patient a drug regime with as few side-effects as possible. The recent technology of creating induced pluripotent stem cells (iPSCs) from patient tissues has allowed the possibility to directly evaluate emerging drugs in cultured human disease-specific cells 11.