Pathobiology of alpha-1-antitrypsin deficency and the serpinopathies

The serine proteinase inhibitors or serpins are a family of proteins that play an important role in controlling enzymes within the human body. Naturally occurring mutations cause the protein to change shape and accumulate as chains of polymers within the cell of synthesis. This causes cell death and hence either cirrhosis (if the protein accumulates within the liver) or dementia (if it accumulates within the brain). We propose to assess the mechanism by which polymers form and their effect on the cells in which they are synthesised. We also propose to determine the mechanism of action of small molecules that we have identified that can block polymer formation in the test tube and reduce the accumulation of mutant protein in a cell model of disease. We have shown that mutations that favour the formation of polymers also favour the formation of an inactive latent conformation. We propose to develop new monoclonal antibodies to the latent conformation of the serpins alpha-1-antitrypsin and neuroserpin so that we can identify them in biological tissues and so evaluate their role in disease. Polymers of alpha-1-antitrypsin form spontaneously within the lungs of individuals with alpha-1-antitrypsin deficiency where they inactivate alpha-1-antitrypsin as a proteinase inhibitor as well as acting as a chemoattractant to recruit inflammatory cells to the lung. We will use our antibody to polymers of alpha-1-antitrypsin to develop a new assay to image pathological polymers within the lung. This will provide useful information on the clearance of polymers from the lung and perhaps the progression of lung disease in individuals with alpha-1-antitrypsin deficiency.

We have used a wide range of techniques 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. Perhaps most striking is our description of 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). A central feature of these conditions is 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 in association with disease. We propose to use the small molecules, crystal structures, cell lines, monoclonal antibodies, fly models and the genetic screen that were generated in the last programme grant to address the following specific questions: (i) what are the conformational transitions underlying the serpinopathies? (ii) what is the effect of small molecules that block the polymerisation of alpha-1-antitrypsin? (iii) what is the cellular response to the retention of ordered serpin polymers within the endoplasmic reticulum? (iv) can we prepare monoclonal antibodies to latent alpha-1-antitrypsin and neuroserpin in order to define their role in disease? (v) what is the role of polymers in lung disease in alpha-1-antitrypsin deficiency? These studies, although focused on alpha-1-antitrypsin and neuroserpin, 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.