Gene therapy of renal diseases and molecular therapies based on the N-terminal acetylation of proteins

Protein N-Terminal Acetylation

Proteins first two amino acids undergo a series of co- and post-translational modifications (acetylation, myristoylation, ubiquitination, methylation, arginilation, peptidases, ...) that define some substantial protein properties (stability, interaction, localization ...). Deregulation of these protein modifications is associated with the development of various pathologies.

More than 85% of eukaryotic proteins are found acetylated on the alpha-amino terminal residue, having begun to be deciphered their particular biological relevance in recent years. We have verified that N-terminal acetyltransferase NatB acetylates the initial methionine whenever it is followed by any of these four amino acids: Glu, Asp, Asn, Gln (Fig 1). We have shown that this enzyme is essential for the organization and proper function of actin cytoskeleton such that inhibition of the enzyme blocks cell motility, thereby affecting the structure and function of one of its substrates: tropomyosin. Our main objective is to identify and characterize the biological functions and pathologies regulated by NatB in order to be able to develop new therapeutic treatments based on the regulation of the activity of this enzyme or the interaction with any of its substrates.

We have recently observed that tropomyosin amino-terminal acetylation is necessary to maintain the hepatic metabolic zonation and murine hepatocytes proper polarity and ploidy. In addition, the catalytic subunit of the NatB enzyme, Naa20, is overexpressed in both human and murine hepatocellular carcinoma. Therefore, we have identified small molecules that are able to inhibit the NatB enzyme to optimize them and use them as a basis for a new anti-tumor and anti-metastatic therapy.

In addition, we want to identify NatB substrates whose biological activity is associated with its amino-terminal acetylation. In collaboration with Dr. Manuela Côrte-Real (Department of Biology Center for Molecular and Environmental Biology, Universidade do Minho Braga Portugal) we have determined the need for NatB mediated BAX amino-terminal acetylation for its subcellular location regulation (Fig 2). At this time, we are evaluating the apoptotic processes regulated by the enzyme NatB.

Together with Dr. Montserrat Arrasate, from CIMA Neuroscience Program, we are determining the relevance of α-synuclein amino-terminal acetylation, modification catalyzed by NatB, in the pathologies associated with this protein (Parkinson's disease and other neurodegenerative diseases). In particular, we are studying how this modification affects the aggregation and stability of the protein and the toxicity-pathogenicity of the most deleterious forms of α-synuclein. The objective is to identify new therapeutic strategies aimed at reducing the pathological aggregation of this protein.

Renal Gene Therapy

10% of the European population suffers from chronic kidney disease. Nearly 70 million Europeans have lost some of their kidney functions and are at great risk of becoming dependent on renal replacement therapies: dialysis and kidney transplantation. Currently available treatments are based on addressing the causes that cause kidney failure, but there are very few options to act on the injuried kidney.

One of the procedures that can help to correct this type of diseases is renal gene therapy. Initially the best type of diseases to be treated by gene therapy are monogenic genetic diseases. A large number of kidney diseases have their origin in deficiencies or mutations in a single gene, counting for a large number of them with a genetic diagnosis that clearly allows the identification of the causal agent of the disease in each patient.

One of the main limitations to make renal gene therapy a reality is the observed limited capacity to transport the genetic material to the different cells of the kidney, unlike other organs such as the liver, brain and eye. The best transporters we have nowadays are those based on viral vectors that have shown that it is possible to reach the kidney efficiently if the administration routes and the appropriate delivery systems are used.

Our goal is to develop adeno-associated virus (AAV) based gene therapy vectors with renal cell types transduction ability. Given that the AAV capsid can be chemically modified without affecting its infectivity, we are exploring the potential of binding different molecules to AAV capsid proteins in order to modify AAV tropism. The link of these molecules to AAV viral particles will allow us their vehiculization to the kidney (Fig 3). Specifically, we will evaluate the potential of recombinant AAVs decorated or not with different ligands to transduce the different renal cell types. The vectors that present best renal transduction capacity will be used to develop gene therapy treatments against renal monogenic diseases such as PKD and cystinosis.

"We have identified small molecules capable of inhibiting the NatB enzyme that may form the basis of a new antitumor and anti-metastatic therapy", Dr. Rafael Aldabe, Principal Investigator.


Cristina López
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