Shaw G, Madorsky I, Li Y, Wang Y, Jorgensen M, Rana S, Fuller DD. Uman-type neurofilament light antibodies are effective reagents for the imaging of neurodegeneration. Brain Commun. 2023;5(2):fcad067. Epub 2023 Mar 16 PubMed.
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University of Florida
I think this is an interesting paper, but I am biased being one of the authors. The neurofilament light polypeptide (NF-L) is an abundant neuron-specific protein heavily expressed in axons. Axons are very sensitive to mechanical and metabolic compromise, and axonal loss is a problem following stroke, traumatic CNS injury, and in disease states such as Alzheimer’s, ALS, multiple sclerosis, and others. It is obvious that axonal injury will result in release of NF-L from damaged axons, and the levels detected in CSF or blood are possibly useful surrogate markers of ongoing axonal loss. Several assays using two key monoclonal antibodies utilized in the Uman NF-Light™ ELISA, including the Quanterix NF-L Simoa™ assay, have been used to trace ongoing axonal loss by measuring NfL not only CSF but also blood samples, including human patient blood. Some sense of the exponential explosion of interest in this biomarker can be seen by searching PubMed for “(NF-L or nfl or NEFL or ‘neurofilament light’) and biomarker.” As of 22 May 2023, this search finds almost 2,500 papers, most produced in the last two to three years. However, exactly what part of the NF-L molecule these two key reagents were detecting was not known.
In this paper we show that the antibodies recognize closely spaced epitopes in the center of the second α-helical region of the NF-L molecule, which should be useful information for the hundreds of labs using these assays. We also found that, surprisingly, both antibodies failed to stain axons, dendrites, or neurons in CNS tissue sections from uninjured animals. Rather, both antibodies selectively bound a small subset of objects that had the appearance of degenerating or degenerated material. This suggested that the epitopes for both antibodies were hidden in normal tissues but exposed upon neurodegeneration, so that the few objects we saw in healthy tissues were likely the result of spontaneous degeneration. In line with this, rats given spinal cord injuries revealed numerous swollen, beaded, sinusoidal and clearly degenerating axons that were strongly stained with both NF-L antibodies. We provided evidence that the epitopes for both antibodies are revealed during degeneration by proteolysis. We also made a novel panel of antibodies to the region containing the Uman epitopes, which all revealed the same interesting degeneration-specific staining pattern.
Since this paper was submitted, we have found that antibodies to multiple sites flanking the Uman epitopes are also hidden in sections from healthy animals but revealed in degenerating material. We propose that the α-helical region containing these hidden epitopes is part of a binding site important for the assembly of neurofilament multimers into mature 10 nm diameter neurofilaments.
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