Familial amyloidosis of the Finnish type (FAF) is an autosomal dominant hereditary amyloid disease. In human

patients, amyloid deposits arc found in the skin, cornea, vascular walls, peritoneum and facial nerves. Clinical

features include peri feral neuropathies affecting the cranial nerves, corneal dystrophy, Clllis /cua, kidney and hean

failure. There is a minor CNS involvement (slight impairment of memory, impairment of visuospatial and

constructional abilities). Amyloid fibrils originate from the secreted actin associated protein ge/solin. FAF is caused

by a single point mutation (Asp 187 to Tyr or Asn). This causes loss of calcium binding by gc1solin domain 2. As a

result, furin (a Ca2+ -dependent serine endoprotease) proteolytically removes an N-terminal segment of gelsolin

during its transpon in the Irans Goigi network, leaving a 68 kDa C-tenninal fragment (C68) (Figure IA). Upon

secretion of C68, the matri!, metalloprotcasc MTI-MMP catalyzes the second proteolytic cleavage of gclsolin

resulting in formation of 8 and 5 k Da gclsolin peptides that associate spontaneously into amyloid fibrils, responsible

for disease onset and progression. A mouse model recapitulating the disease was published by the group of Dr.

Kelly (Scripps Researeh Institute, USA).

A classical approach for treating this type of disease would be to usc inhibitors of furin or MTI-MMP. However,

given the chronic nature (of many amyloid diseases) this would very likely cause undesirable side effects. We plan

to usc a different strategy which can also be extended to other amyloid diseases, i.e. by employing nanobodies. We

raised different sels ofnanobodies against gc1solin with the aim of protecting FAF mutant gelsolin against furin or

MTI-MMP cleavage. Nanobodies arc the smallest intact antigen-binding fragments from heavy chain antibodies

present in serum ofCamelidae (Figure I B). They can be easily cloned, expressed and purified. Our work has shown

that selected gelsolin nanobodies can protect gelsolin cleavage in vitro and in vivo. We engineered the first

nanobody transgenic mouse that purportedly will protect gelsolin against rurin attack. Because of their unique

biophysical and pharmacological propenies, nanobodies represent a promising tool for research, and arc ideally

suitcd to devclOP into a new class of thcrapcuties. Our aims im:ludc: I) to investigate nanobody thcrapeutic clTecls

in transgcnic animals, 2) to usc nanobodics for in vivo imaging of amyloid deposits, 3) to develop a nanobody

endowed a with a double protective activity and 4) to pinpoint the exact binding site in gelsolin ofa nanobody that

protccts against MTI-MMP activity.

Hence, targeting the amyloidogenic substrates with nanobodies may develop into an approach useful in other

amyloid diseases.