Gelsolin amyloidosis (AGel) is an autosomal‐dominant inherited disease caused by point mutations in the gelsolin gene. At the protein level, these mutations result in the loss of a Ca2+‐binding site, crucial for the correct folding and function. In the trans‐Golgi network, this mutant plasma gelsolin is cleaved by furin, giving rise to a 68 kDa C-terminal fragment. When secreted in the extracellular matrix, this fragment undergoes proteolysis by MT1‐MMP–like proteases, resulting in the production of 8 and 5 kDa amyloidogenic peptides. Nanobodies, the variable part of the heavy chain of heavy‐chain antibodies, have been used as molecular chaperones for mutant plasma gelsolin and the 68 kDa C‐terminal fragment in an attempt to inhibit their pathogenic proteolysis. Furthermore, these nanobodies have also been tested and applied as a 99mTc‐based imaging agent in the gelsolin amyloidosis mouse model.
Part of the book: Exploring New Findings on Amyloidosis
The discovery of heavy-chain-only antibodies (HCAbs) in camelids and sharks led to the rise of a new research field in which single-domain antibodies are used for various applications. Single-domain antibodies are the antigen-binding fragments derived from HCAbs showing several beneficial properties (e.g., small size, specificity, stability under extreme conditions, cost-effective production, and ease of engineering). Importantly, they are stable in reducing cytoplasmic environment, which allows their use as an intrabody to target a wide range of intracellular targets. In this chapter, we discuss both the therapeutic potential of camelid single-domain antibodies (nanobodies) and their use as a research tool with the main focus on its intracellular employment. Targeting intracellular proteins using nanobodies as a therapeutic per se is, up to now, limited due to its incapacity to traverse the cellular membrane. They can however serve as a stepping stone to small compound development, since they directly target a resident, endogenous protein, similar to how a conventional drug acts. In addition, nanobodies are highly adaptable tools and possess interesting properties for more fundamental research objectives like the elucidation of protein function, the tracking and visualization of endogenous proteins in an in vivo setting, and the assessment of protein-protein interactions.
Part of the book: Antibody Engineering