Henrique Girão, Group Leader
Many of the degenerative and age-related diseases are associated with endothelial dysfunction and in many cases with abnormal angiogeneis (neovascularization), such as diabetes retinopahty, heart ischemia and cancer. Proliferation of endothelial cells and the formation of new blood vessels are, in part, regulated by the transcription factor Hypoxia Inducible Factor (HIF). One of our major objectives is to understand the molecular mechanisms and signalling events that may interfere with proteasome-dependent degradation of HIF-1α, leading to abnormal retinal vessel proliferation. For example we have provided evidence to shown that inactivation of critical components of the ubiquitin-proteasome pathway in retinal pigmented epithelial cells (RPE) may contribute for cellular and organ alterations associated with AMD, including the neovascular component (wet form of AMD) and the inflammatory component.
It has been suggested that aging affects the cells ability to protect protein integrity, which is essential for cellular homeostasis, maintained by a complex system of refolding or degradation, such as ubiquitin-proteasome pathway (UPP) and lysosome pathway (autophagy). The carboxyl terminus of Hsp70-interacting protein (CHIP) interacts with Hsp70 and Hsp90 via three tandem tetratricopeptide repeat motifs, whereas it’s carboxyl-terminal U-box domain associates with ubiquitin-conjugating enzymes. A major objective in this area is to elucidate the role of CHIP in the protein quality control in a number of diseases such as cataract, using an animal model that overexpresses CHIP in the lens epithelial cells, examine the lens transparency and correlate with changes in lens proteins and degradation markers.
AMD is also characterized by the accumulation of subretinal deposits and drusens. Even though the association between proteasomal disruption and accumulation of drusen-like deposits is not obvious, it was recently suggested that an age-dependent increase in the autophagic flux, as a result of proteasome inhibition, would overload the lysosomal system and subsequently lead to accumulation of subcellular deposits containing unprocessed material in the form of drusens. We are currently using an animal model of AMD, with impaired protein degradation through the proteasome, as a tool to investigate the biological determinants of age-related proteolytic stress and its impact on proteostasis in the retina and presumably in other tissues affected by age-related diseases.
It is now widely accepted that ubiquitin-conjugation not only helps destroy damaged proteins in the proteasome but is also involved in downregulation and lysosomal degradation of membrane proteins. One of the objectives of this proposal is to study the role of ubiquitin in the regulation of internalization and intra- cellular trafficking of membrane proteins. We are particulary interested in elucidating the mechanisms and molecular players involved in the degradation of the gap junction protein (GJ) Cx43. GJ are specialized cell–cell contacts that provide direct intercellular communication (IC) between eukaryotic cells, playing a vital role in regulating cell homeostasis, proliferation and differentiation and maintain homogeneous tissue function. GJIC can be regulated at various levels, including the number of channels localized at the plasma membrane, being ubiquitin-dependent internalization and degradation of GJ one of the mechanisms involved in this regulation. Defects in GJIC are often associated with disease, such as cataract, diabetic retinopathy, neurological disorders, cancer and cardiomyopathies. A major objective of our group is to investigate how Cx43 degradation may contribute to cancer and heart diseases, in particular how ubiquitin signal determines the degradation pathway followed by Cx43, either through the endocytic or the autophagic pathway.
PhD - Investigator
PhD - Investigator
|João Carlos Ribeiro MD - PhD Student||Rui Batista MD - PhD Student|
Sara Ramos MD - PhD Student
Ana Paula Vieira
MSc - Research Fellow
BSc - Research Fellow