Biomedical
A Quantitative Perspective of Alpha-Synuclein Dynamics – Why Numbers Matter
Abstract
The function of synapses depends on spatially and temporally controlled molecular interactions between synaptic components that can be described in terms of copy numbers, binding affinities, and diffusion properties. To understand the functional role of a given synaptic protein, it is therefore crucial to quantitatively characterise its biophysical behaviour in its native cellular environment. Single molecule localisation microscopy (SMLM) is ideally suited to obtain quantitative information about synaptic proteins on the nanometre scale. Molecule counting of recombinant proteins tagged with genetically encoded fluorophores offers a means to determine their absolute copy numbers at synapses due to the known stoichiometry of the labelling. As a consequence of its high spatial precision, SMLM also yields accurate quantitative measurements of molecule concentrations. In addition, live imaging of fluorescently tagged proteins at synapses can reveal diffusion dynamics and local binding properties of behaving proteins under normal conditions or during pathological processes. In this perspective, it is argued that the detailed structural information provided by super-resolution imaging can be harnessed to gain new quantitative information about the organisation and dynamics of synaptic components in cellula. To illustrate this point, I discuss the concentration-dependent aggregation of α-synuclein in the axon and the concomitant changes in the dynamic equilibrium of α-synuclein at synapses in quantitative terms.
Why is quantitative analysis important for studying synaptic proteins like α-synuclein?
Quantitative analysis is crucial because:- Many biological phenomena are concentration-dependent
- Changes in protein distribution are best evaluated on a linear scale
- Quantitative data can be directly compared between different laboratories and experimental approaches
- Biophysical models rely on quantitative parameters to describe biological phenomena mathematically
What advantages does single molecule localization microscopy (SMLM) offer for quantitative analysis?
SMLM provides several advantages:- Achieves localization precision of 10-20 nm
- Provides exact quantitative readout in the form of single molecule detections
- Allows for absolute quantification, converting detections into actual molecule numbers and packing densities
- Has theoretically unlimited dynamic range from true zero up to closely packed fluorophores
- Offers single-molecule sensitivity
How does α-synuclein contribute to Parkinson's disease pathology?
α-synuclein contributes to Parkinson's disease through:- Formation of β-sheeted fibrils that aggregate in neurons
- Accumulation in Lewy bodies, the hallmark of Parkinson's disease
- Gene mutations that increase its propensity to aggregate
- Gene duplications or triplications leading to overexpression and increased aggregation
