Applications of Laser Capture Microdissection in the Study of Neurodegenerative Disease

Abstract

Laser capture microdissection (LCM) is a new technology that is becoming increasingly important for studies of neurodegenerative disorders. A characteristic feature of all neurodegenerative diseases is “selective vulnerability.” In each of the disorders, there is selective degeneration of particular types of neurons, with relative preservation of much of the rest of the brain. Familiar examples are the selective degeneration of dopaminergic neurons in Parkinson disease, the striking depletion of basal forebrain cholinergic neurons in Alzheimer disease, the selective atrophy of the caudate nucleus in Huntington disease, and the loss of spinal motor neurons in amyotrophic lateral sclerosis. Closer examination reveals an even more finegrained pattern of neuronal injury. For example, in Parkinson disease there is striking depletion of dopaminergic neurons in the ventral tier of the substantia nigra pars compacta, with very little injurytodopaminergicneuronslocatedonlyafewmillimetersawayinthedorsaltierofthenucleus. In Huntington disease, there is an exquisite degree of selectivity among the different types of neurons found within the caudate and putamen, with striking depletion of the medium spiny projection neurons, especially those projecting to the globus pallidus, in contrast to preservation of the intermingled interneurons. These characteristic patterns of injury are evident even in genetically determined forms of neurodegenerative disease where the fundamental defect can be shown to be present in all neurons. Understanding the basis for these patterns of neuronal loss may provide important insight into the mechanisms of neurodegeneration. Selectivevulnerabilitycreatesdifficulttechnicalchallengesforinvestigatorsattempting to apply modern molecular methods to the study of disease. Many of the currentmethodsforanalyzingDNA,messengerRNA(mRNA)andproteinsrelyonhomogenization and extraction of the chemical elements of interest. Until recently,moststudiesofthisnaturehaverelied on studies of anatomical regions at least several millimeters in size, and often much larger. These areas are large enough that they unavoidably encompass both affected and unaffected neuronal populations. They also include a large component of glial structures, which may have their own distinct role in and responsetoneurodegeneration.Thedataobtained by homogenization of such heterogeneous samples are often difficult to reconcile with alterations in the biology ofspecificpopulationsofcomponentcells. Researchers can use LCM as an accessible method for separating the different cell types present in a brain region, and are able to study the biology of homogeneous cell populations with specific characteristics.