Pathobiology of the serpinopathies

We have previously described a new class of disease that we have called the serpinopathies. These occur as a result of mutations in members of a family of proteins called the serine protease inhibitors or serpins. Mutations in these proteins cause them to change size and shape with either aberrant tissue deposition or loss of function. The serpinopathies encompass a wide spectrum of disease that is as diverse as cirrhosis, thrombosis, angioedema, emphysema and more recently dementia. We now propose to define the mechanisms by which mutations in members of the serpin superfamily cause the serpinopathies. In particular, we will use protein, cell and fly models to define how the abnormal proteins form, how they are handled by cells and how they cause cell death. In addition we will develop antibodies to neuroserpin so that we can detect the abnormal protein in animal and human tissues. Finally, we will define how the body clears these abnormal conformations of protein from the circulation and how they can excite white cells to cause inflammation and further tissue damage. Taken together, this programme of work will provide new insights into many different conditions. It is the long-term aim of our laboratory to develop strategies to treat the wide range of diseases that comprise the serpinopathies.

We have used biochemistry, biophysical analysis, crystallographic studies, cell biology, monoclonal antibodies, fly and mouse models to show that naturally occurring mutations in members of the serine proteinase inhibitor (serpin) superfamily result in abberant conformational transitions to cause disease. The most common of these is the sequential linkage between the reactive centre loop of one molecule and beta-sheet A of another. This process of loop-sheet polymerisation results in the retention of ordered serpin polymers within the cell of synthesis. Polymerisation of mutants of antitrypsin, antithrombin, C1 inhibitor and antichymotrypsin cause cirrhosis, thrombosis, angioedema and emphysema respectively. More recently we have described the same process in a neurone specific serpin, neuroserpin, to cause a novel dementia that we have called Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB). We have now described 4 mutants of neuroserpin that cause FENIB and have demonstrated a genotype-phenotype correlation that can be explained by the rate of intracellular polymerisation. In view of their common mechanism we have grouped these diseases of the serpins together as the serpinopathies and have used them as a paradigm for a broader class of disorders that we have called the conformational diseases. The serpinopathies provide a structurally defined model of protein aggregation that causes disease. We propose to use biochemistry, cell biology and fly models to address the following questions in this programme of work: a) What are the pathways that underlie conformational transitions of neuroserpin and can we develop strategies to block polymerisation in vitro and in vivo? b) How are polymers handled by neurones? c) How do polymers cause cell death in a Drosophila model of a serpinopathy? d) Can we develop monoclonal antibodies to detect polymeric neuroserpin in vitro and in vivo? and e) How are polymers cleared from the circulation and how do they mediate their pro-inflammatory effects within the lung? These studies, although focused on neuroserpin and a1-antitrypsin, are applicable to many of the mutations in serpins that underlie the serpinopathies. The long-term aim of our work is to understand mechanisms of disease caused by the serpinopathies (from pathological conformational transitions to pathways of cell toxicity) so that we can develop novel therapeutic strategies to treat the associated clinical syndromes.