Fluorescent Biomarkers in Neurons

Functional imaging has become one of the main ways to study the functions of different neurons, from subcellular studies of dendritic spines dynamics to whole-cell circuit-level imaging, to mesoscale, and chronic whole-brain imaging in small animals. Therefore, multiple tools are needed to study different aspects of neuronal signaling and function. Fluorescent molecular probe is a kind of non-genetically coded biosensor for directly labeling neurotransmitters developed in recent years. In the research of neurodegenerative diseases, fluorescent probe-mediated biomarker visualization technology has attracted more and more attention in the early diagnosis of neurodegenerative diseases.

Fluorescent Protein (FP) Sensor

Fluorescent protein (FP)-based sensors include cyclic permutation FP (cpFPs) scaffolds and fluorescence resonance energy transfer (FRET)-based reporters. These small molecules have reactive functional groups, such as aldehydes or hydroxides, that react with the target analyte or the environment to trigger the fluorescence of the biosensor. Traditionally, fluorescent molecules or proteins have been used as tags for target cells. However, in neuroscience research, fluorescence imaging is also being developed to track dynamic processes such as action potentials, calcium changes, or neurotransmitter release in vivo and in vitro.

Fig.1 Structure of cpFP sensors and mechanism, Structure of FRET sensors and mechanisms. (Zhou, 2020)

Fluorescent Biomarkers in Neurons

• GABAA receptors

Ligand-based probes have also been used to screen potential drugs that may selectively bind to targeted receptors. GABAA receptor (GABA AR) can covalently label the fluorophore near the binding site, without affecting the binding of these compounds to the bimolecular fluorescence quenching and recovery, making the construction of fluorescent GABA AR ligand biosensors on the surface of living cells possible.

• Ionotropic glutamate (iGlu) receptors

The probe used to display ionic glutamate (iGlu) receptors are synthesized based on fluorescent polyamine toxin analogs. The use of the natural product argiotoxin-636 (ArgTX-636) can block iGlu receptor ion channels. This probe is used to observe the natural NMDA receptor neurons in the hippocampus.

• Fluorescent false neurotransmitters (FFNs)

FFNs are optical probes for monoamine neurotransmission, usually composed of small fluorescent compounds and a recognition element, such as the ethylamine moiety. The research of FFNs mainly focuses on the synaptic control of neurotransmitter release: FFNs are loaded into vesicles to observe the presynaptic terminals and the release and uptake of neurotransmitters.

• Quantum dots (QDs)

QDs are light-emitting semiconductor nanoparticles. Modification of QDs with antibodies or small molecule ligands can make them specifically bind to target proteins or cells to emit red light. QDs can be used to visualize dopamine receptors in vivo.

• Curcumin derivatives

Due to the low fluorescence quantum yield of curcumin, the application of bioimaging was limited. Therefore, curcumin derivatives, CRANAD compounds, are prepared by converting the internal body into the corresponding Boron complex and substituting different aromatic groups for the curcumin acrylic group. Fluorescence is enhanced when the CRANAD compound binds to amyloid β (A+) plaques when tested in Alzheimer's disease (AD) samples.

• Fluorescent antibody

Calbindin S100β, excitatory amino acid transporter (EAAT1+2), aldehyde dehydrogenase-1 family (ALDH1L1), sulfophosamine 101 (SR101) selectively stains astrocytes. These fluorescent antibodies selectively stain astrocytes, reactive astrocytes fluoresced in the red area when they are diseased.

Application of Fluorescent Probes in Degenerative Diseases

A+ plaques and neurofibrillary tangles (NFTs) are the two main pathological signs of AD. This prospect outlines the use of small fluorescent molecules to target AD biomarkers for pre-in vivo and in vivo imaging, providing significant advances in AD diagnostic technology.

Fig.2 The chemical structure of the probe used to detect amyloid-β species (Aβs) and the newly designed near-infrared probes. (Jun, 2019)

The neurodegenerative process begins long before clinical symptoms become apparent and has progressed slowly and irreversibly. It is urgent to diagnose and distinguish the common and unique characteristics of different neurodegenerative diseases. Fluorescent marker-mediated probe technology has made a great contribution to the analysis of cognitive dysfunction and provides a deep understanding of the diagnosis of neurological diseases.

Creative Biolabs has a variety of reliable products in the diagnosis of neurodegenerative diseases. Our multiple fluorescein products can help you efficiently label the system and improve research efficiency and progress. Please feel free to contact us if you are interested or have any questions.

References

1. Zhou, J.; et al. Fluorescent diagnostic probes in neurodegenerative diseases. Advanced Materials. 2020, 32(51): 2001945.
2. Jun, Y.W.; et al. Frontiers in probing Alzheimer’s disease biomarkers with fluorescent small molecules. ACS central science. 2019, 5(2): 209-217.