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INTRODUCTION: The insulin-regulated aminopeptidase (IRAP) is expressed in several cell types, where it is mainly located in specialized secretory endosomes that are quickly recruited to the cell surface upon cell type-specific activation. Here we describe for the first time the expression and subcellular distribution of IRAP in macrophages. METHODS: IRAP mRNA expression, protein expression and presence at the cell surface was investigated by real-time polymerase chain reaction (PCR), Western blot and [(3)H]IVDE77 binding, respectively. RESULTS: IRAP mRNA expression was increased by interferon-γ (IFN-γ) and lipopolysaccharide (LPS), but not by anti-inflammatory cytokines (interleukin (IL)-4, IL-10, transforming growth factor β (TGF-β)). IFN-γ increased [(3)H]IVDE77 binding steadily over time, while LPS quickly and transiently recruited IRAP to the cell surface. Combined stimulations with IFN-γ and LPS showed the same pattern as LPS alone. Latex particles also induced a transient recruitment of IRAP to the cell surface, but no difference was observed in phagocytic uptake between wild-type and IRAP(-/-) macrophages, suggesting that the enzymatic activity of IRAP is not required for the ingestion of particles. CONCLUSION: IRAP is more highly expressed in pro-inflammatory M1-activated macrophages and its presence at the cell surface is modulated upon exposure to IFN-γ, LPS or exogenous particles.

Since the discovery of a renin-angiotensin system (RAS) in the brain, several studies have linked this central RAS to neurological disorders such as ischaemia, Alzheimer’s disease and depression. In the last decade, evidence has accumulated that the central RAS might also play a role in Parkinson’s disease. Although the exact cause of this progressive neurodegenerative disorder of the basal ganglia remains unidentified, inflammation and oxidative stress have been suggested to be key factors in the pathogenesis and the progression of the disease. Since angiotensin II is a pro-inflammatory compound that can induce the production of reactive oxygen species due to activation of the NADPH-dependent oxidase complex, this peptide might contribute to dopaminergic cell death. In this review, three different strategies to interfere with the pathogenesis or the progression of Parkinson’s disease are discussed. They include inhibition of the angiotensin-converting enzyme, blockade of the angiotensin II type 1 receptor and stimulation of the angiotensin II type 2 receptor.

To explain the insurmountable/long-lasting binding of biphenyltetrazole-containing AT 1-receptor antagonists such as candesartan, to the human angiotensin II type 1-receptor, a model is proposed in which the basic amino acids Lys 199 and Arg 167 of the receptor interact respectively with the carboxylate and the tetrazole group of the antagonists. To validate this model, we have investigated the impact of substitution of Lys 199 by Ala or Gln and of Arg 167 by Ala on the binding properties of [ 3 H]candesartan and on competition binding by candesartan, EXP3174, irbesartan, losartan, angiotensin II (Ang II) and [Sar 1 -Ile 8 ]angiotensin. Our results indicate that both amino acids play an important role in the AT 1-receptor ligand binding. Whereas the negative charge of Lys 199 is involved in an ionic bond with the end-standing carboxylate group of the peptide ligands, its polarity also contributes to the non-peptide antagonist binding. Substitution of Arg 167 by Ala completely abolished [ 3 H]Ang II, as well as [ 3 H] candesartan, binding. Whereas these results are in line with the proposed model, it cannot be excluded that both amino acid residues are important for the structural integrity of the AT 1-receptor with respect to its ligand binding properties.