Ricerc@Sapienza

We study a group of protein conformational diseases caused by polymerisation of mutant serpins (serin proteinase inhibitors), specifically the neuronal protein neuroserpin and the hepatic serpin alpha-1 antitrypsin. The mechanism of inhibition of serpins requires a high molecular flexibility that renders them very sensitive to destabilising mutations. The mutant variants undergo polymerisation within the endoplasmic reticulum of the cell of synthesis, which prevents their normal trafficking and secretion. This leads to disease with both gain- and lack-of-function phenotypes, due to intracellular polymer accumulation and lack of active serpin in the place of action, respectively.

In the case of neuroserpin, polymerisation causes a very rare neurodegenerative condition called familial encephalopathy with neuroserpin inclusion bodies (FENIB), with an onset of disease that correlates to polymerisation propensity of each variant. We have developed a cell culture model consisting in mouse neural progenitor stem cells overexpressing wild type or polymerogenic neuroserpin, which can be differentiated to neurons in vitro. Using this system, we have shown that neuroserpin polymers cause oxidative stress and mitochondrial alterations, consisting in perinuclear clustering and decrease of the inner membrane potential. Mitochondrial mislocalisation is enhanced by prooxidant molecules and rescued by antioxidants. These results highlight the role of oxidative stress and mitochondrial damage in FENIB.

In alpha-1 antitrypsin deficiency, polymerisation of the mutant protein leads to the lack of active alpha-1 antitrypsin in the lungs, causing emphysema, while polymer retention within hepatocytes causes liver disease. We have developed a set of conformation-specific and functional monoclonal antibodies against alpha-1 antitrypsin that we have used in collaboration to study polymer formation and structure, and the role of these polymers in disease.