Healthy & Diseased Tissue Compared
A recently published academic work, yet one with commercial implications, used Protein Tomography to elucidate the role of nephrin protein in in vivo plasma filtration in the kidney (Journal of Clinical Investigation, 2004, 114, 1475-1483). Nephrin is the key functional component of the slit diaphragm that acts as a filter in renal glomerular capillaries. Healthy and diseased (nephrin-deficient proteinuric patients with congenital nephrotic syndrome of the Finnish type [NPHS1]) tissue from humans was compared at the molecular level. Tissue from rats and mice was also examined.
Tomograms revealed a clear difference in the filter structure between healthy individuals and NPHS1 patients (Figure 2). The healthy slit (A) was wide (approximately 35 nm) and contained the slit diaphragm structure with small pores. Strands were found corresponding to the extracellular part of nephrin (approximately 34 nm long). The slit in NPHS1 patients was collapsed and lacked the nephrin-type strands (width approximately 15 nm), this contributed to a much more disorganized structure, presumably allowing the leakage of plasma proteins.
As Protein Tomography data can be used for comparison between different types of tissue and proteins in solution, further studies were initiated, namely visualizing the structure of full-length nephrin in transfected cells and individual recombinant nephrin molecules in solution.
These tomograms showed that the recombinant nephrin molecules have a 35-nm elongated form. The structural similarity of nephrin in cells and in solution was clear. Similar length strands were found in healthy slit diaphragms, strongly suggesting that they to a large extent consist of extracellular portions of nephrin molecules.
In addition, Protein Tomography data revealed a similar slit diaphragm structure in mouse and rat kidney, showing that kidney filter morphology is conserved in different species. This finding suggests that animal models most probably are relevant systems for further studies of the human biology of the kidney filtration barrier.
By taking 3-D pictures of proteins, Protein Tomography allows researchers to see biomolecules in their cellular context. Tomograms provide insights into the conformation and flexibility of functional targets and their environment.
Protein Tomography data helps elucidate underlying disease mechanisms and can thus help make stop/go decisions earlier in the drug discovery process. It also has the potential to explain the differences between nonresponders and responders at a molecular level. Protein Tomography also supports the development of biologically relevant assays and model systems reducing the risk of failure in drug discovery projects.