Nervous System: Cell Replacement Therapy

Question 1

Cell Replacement Therapy

Answer 1

• Any disorder involving loss of, or injury to, normal cells is a potential candidate for stem cell replacement therapy
• However, cell replacement therapy for the nervous system has generated the most interest due to the debilitating nature and widespread occurrence of neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases
• The most attractive method for restoring brain function in, say, Parkinson’s disease is the replacement of dying neurons with healthy neuronal tissue.
• Pilot studies using embryonic stem cells have been carried out in humans with some success.
• The transplanted cells not only survived but also grew and established connections with adjacent neurons.
• Recent developments with neural crest stem cells from adults have had encouraging results.
• These cells, sourced from adult hair follicles, are similar to embryonic stem cells because they are able to differentiate into many diverse cell types.
• Research into blood disorders has identified multipotent adult progenitor cells (MAPCs).
• These cells, produced from bone marrow, appear to be able to divide endlessly in culture, overcoming a problem that exists with other cells sourced from bone marrow.

Question 2

Alzheimer’s Disease

Answer 2

• The cause of Alzheimer’s disease is poorly understood.
• There are many environmental and genetic risk factors associated with its development.
• The disease process is largely associated with amyloid plaques, neurofibrillary tangles, and loss of neuronal connections in the brain.
• Good nutrition, physical activity and engaging socially are known to be of benefit generally in aging, and these may help in reducing the risk of cognitive decline and Alzheimer’s.
• There are no medications or supplements that have been shown to decrease risk.
• No treatments stop or reverse its progression, though some may temporarily improve symptoms.

Question 3

Parkinson’s Disease

Answer 3

• Parkinson’s is a long-term degenerative disorder of the central nervous system that mainly affects the motor
  system.
• The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms become more common.
• The most obvious early symptoms are:
• tremor
• rigidity
• slowness of movement
• difficulty with walking.
• Cognitive and behavioural problems may also occur with:
• Depression
• Anxiety
• Apathy.
• The motor symptoms of the disease result from the death of cells in the substantia nigra, a region of the midbrain, leading to a dopamine deficit.
• The cause of this cell death is poorly understood but involves the build-up of proteins in the neurons.
• The cause of PD is unknown, with
  both inherited and environmental factors believed to play a role.
• No cure for PD is known; treatment aims to reduce the effects of the symptoms.
• Initial treatment is typically with the medications levodopa or dopamine agonists.
• As the disease progresses, these medications become less effective, while at the same time producing a side effect marked by involuntary muscle movements.

Question 4

Tissue Engineering

Answer 4

• Stem cells are increasingly being used for tissue engineering.
• The primary objective of tissue engineering is to restore healthy tissues or organs for patients and thus eliminate the need for tissue or organ transplants, or artificial implants.
• Tissue engineering requires an abundant supply of disease-free cells of specific types.
• These cells then need to be induced to grow on a scaffold of natural or synthetic material to produce a three-dimensional tissue.
• Tissue engineering scaffolds serve as a template for tissue growth and need to have high pore sizes that enable the cells to grow while at the same time allowing the diffusion of nutrients throughout the whole structure.
• They frequently need to be biodegradable so that they can be absorbed by the surrounding tissues without having to be removed surgically.
• This needs to be carefully established as the rate the scaffold degrades needs to match, as far as possible, the rate of tissue formation.
• Natural materials, such as collagen or fibrin, derived from the filamentous structures surrounding cells have been used to construct scaffolds, as well as synthetic materials such as polylactic acid.
• This substance degrades to form lactic acid, a naturally occurring chemical that is easily removed from the body.
• Once a scaffold has been created, suitable stem cells need to be cultured and then seeded onto the scaffold for further cell growth and proliferation.
• This cell-covered scaffold is then implanted into the patient, at the site where new tissue is required.
• As the new cells continue to grow and divide the material making up the scaffold begins to degrade or, in some cases, to be absorbed.
• Such tissue engineering techniques are being used to develop a wide range of tissues, including bone, skin, cartilage and adipose tissues.