Alzheimer’s disease is the most common cause of dementia. During the progression of the disease, protein plaques and neurofibrilllary tangles develop in the brain.
The senile plaques that form are dense, insoluble deposits of amyloid-β peptide (Aβ) and other materials which accumulate outside and around neurons. Neurofibrillary tangles are the result of protein aggregation within the cell. The neuron cytoskeleton is a supporting structure made up of microtubules which serve to guide molecules between the body of the cell to the end of the axon.
The microtubule-associated Tau protein becomes hyperphosphorylated and then aggregates with other threads producing neurofibrillary tangles and disrupting the neuron’s transport system.
Amyloid Precursor Protein (APP)
Amyloid Precursor Protein (APP) is an integral membrane protein with concentrated expression in neuron synapses. It is the precursor of Aβ which accumulates in the brains of Alzheimer’s sufferers. APP is subject to cleavage by the proteolytic secretase enzymes (α-, β- and γ-secretase).
The predominant processing pathway for APP is proteolysis by α-secretase, which cleaves APP within the fragment that gives rise to Aβ, hence the α-secretase pathway precludes Aβ formation. β–secretase (also known as β-site APP Cleaving Enzyme 1 or BACE1) cleavage results in a membrane bound fragment known as C99. Subsequent cleavage by γ-secretase produces Aβ.
This has led to interest in β-secretase inhibitors which may prevent or slow the build up of Aβ and be of therapeutic use in the management of Alzheimer’s disease.
Amyloid β ELISAs
Aβ peptides can exist in both 40 and 42 amino acid forms. Aβ42 aggregates more readily than Aβ40, early stage, diffuse plaques may be positive for Aβ42 but negative for Aβ40.
Plaques containing Aβ40 may only appear in the more advanced stages of disease. Post-translational modifications of Aβ have been reported, typically affecting the N-terminus, which may influence protein solubility and aggregation.
Wako offers an extensive range of ELISA assay kits for detection of Aβ peptides in various human and rat samples including plasma, cerebrospinal fluid, tissue homogenate or cell culture media. Kit options to measure full peptide and N-terminal variants for both Aβ 42 and Aβ40 are available.
Tau proteins are microtubule-associated proteins that are mainly expressed in neurons within the central nervous system. They serve to regulate microtuble stability but in tauopathologies such as Alzheimer’s disease this process appears to be defective resulting in pathological aggregation of tau protein in neurofibrillary or gliofibrillary tangles.
These tangles are composed of accumulated phosphorylated Tau protein and the degree of neurofibrillary tangles correlates with disease severity.
There are six isoform of Tau, subclassified to reflect the number of microtuble association domains present, so 3R-Tau and 4R-Tau have 3 and 4 binding sites respectively.
Wako offers monoclonal antibodies for detection of human 3R-Tau and 4R-Tau for Western Blot and immunoprecipitation protocols. In addition, antibodies that specifically recognise Tau protein with phosphorylation at Threonine 181 or Serine 199 are also offered for immunohistochemistry applications.