Óscar Lorenzo

Inflammation and angiotensin II

Angiotensin II (AngII), the major effector peptide of renin-angiotensin system (RAS), is now recognized as a growth factor that regulates cell growth and fibrosis, besides being a physiological mediator restoring circulatory integrity. In the last few years, a large number of experimental studies has further demonstrated that AngII is involved in key events of the inflammatory process. Here, we summarize the wide variety of AngII functions and discuss them in relation with the inflammatory cascade. AngII increases vascular permeability (via the release of prostaglandins and vascular endothelial cell growth factor or rearrangement of cytoskeletal proteins) that initiates the inflammatory process. AngII could contribute to the recruitment of inflammatory cells into the tissue through the regulation of adhesion molecules and chemokines by resident cells. Moreover, AngII could directly activate infiltrating immunocompetent cells, including chemotaxis, differentiation and proliferation. Recent data also suggest that RAS activation could play a certain role even in immunologically-induced inflammation. Transcriptional regulation, predominantly via nuclear factor-kappaB (NF-kappaB) and AP-1 activation, and second mediator systems, such as endothelin-1, the small G protein (Rho) and redox-pathways are shown to be involved in the molecular mechanism by which AngII exerts those functions. Finally, AngII participates in tissue repair and remodeling, through the regulation of cell growth and matrix synthesis. In summary, recent data support the hypothesis that RAS is key mediator of inflammation. Further understanding of the role of the RAS in this process may provide important opportunities for clinical research and treatment of inflammatory diseases.

Proinflammatory actions of angiotensins

Many experimental data have suggested that the renin-angiotensin system participates in immune and inflammatory responses. Angiotensin II is involved in several steps of the inflammatory process: mononuclear cells respond to angiotensin II stimulation (cell proliferation and chemotaxis); angiotensin II regulates the recruitment of proinflammatory cells into the site of injury (mediated by the expression of vascular permeability factors, adhesion molecules and chemokines by resident cells); inflammatory cells can produce angiotensin II, and might therefore contribute to the perpetuation of tissue damage. In this review, we summarize the proinflammatory properties of angiotensin II, to demonstrate the novel role of this vasoactive peptide as a true cytokine. We will show the information obtained as a result of the pharmacological blockade of the renin angiotensin system, which has demonstrated that this system is involved in immune and inflammatory diseases. In this aspect, we discuss the molecular mechanism of angiotensin II-induced tissue damage, as well as its contribution to the pathogenesis of several diseases, including atherosclerosis, hypertension and renal damage, showing that angiotensin II plays an active role in the inflammatory response of these diseases.

Connective Tissue Growth Factor Is a Mediator of Angiotensin II–Induced Fibrosis

Background—Angiotensin II (Ang II) participates in the development of fibrosis during vascular damage. Connective tissue growth factor (CTGF) is a novel fibrotic mediator. However, the potential link between CTGF and Ang II has not been investigated. Methods and Results—In vivo Ang II effects were studied by systemic infusion into normal rats to evaluate CTGF and extracellular matrix protein (ECM) expression by immunohistochemistry. In aorta of Ang II–infused rats, CTGF staining was markedly increased and ECM overexpression was observed. An AT1 antagonist diminished CTGF and ECM. In growth-arrested vascular smooth muscle cells, Ang II induced CTGF mRNA expression after 1 hour, remained elevated up to 24 hours, and increased CTGF protein production, which was increased up to 72 hours. The AT1 antagonist blocked Ang II–induced CTGF gene and protein expression. Early CTGF upregulation is independent of new protein synthesis. Several intracellular signals elicited by Ang II are involved in CTGF synthesis, including protein kinase C activation, reactive oxygen species, and transforming growth factor-&bgr; endogenous production. Incubation with a CTGF antisense oligonucleotide decreased CTGF and fibronectin upregulation caused by Ang II. Conclusions—Our results show that Ang II, via AT1, increases CTGF in vascular cells both in vivo and in vitro. This novel finding suggests that CTGF may be a mediator of the profibrogenic effects of Ang II in vascular diseases.

Angiotensin II, via AT1 and AT2 Receptors and NF-κB Pathway, Regulates the Inflammatory Response in Unilateral Ureteral Obstruction

Inflammatory cell infiltration plays a key role in the onset and progression of renal injury. The NF-kappaB participates in the inflammatory response, regulating many proinflammatory genes. Angiotensin II (Ang II), via AT(1) and AT(2) receptors, activates NF-kappaB. Although the contribution of Ang II to kidney damage progression is already established, the receptor subtype involved in the inflammatory cell recruitment is not clear. For investigating this issue, the unilateral ureteral obstruction (UUO) model was used in mice, blocking Ang II production/receptors and NF-kappaB pathway. Two days after UUO, obstructed kidneys of wild-type mice presented a marked interstitial inflammatory cell infiltration and increased NF-kappaB activity. Treatment with AT(1) or AT(2) antagonists partially decreased NF-kappaB activation, whereas only the AT(2) blockade diminished monocyte infiltration. Obstructed kidneys of AT(1)-knockout mice showed interstitial monocyte infiltration and NF-kappaB activation; both processes were abolished by an AT(2) antagonist, suggesting AT(2)/NF-kappaB involvement in monocyte recruitment. In wild-type mice, only angiotensin-converting enzyme inhibition or combined therapy with AT(1) plus AT(2) antagonists blocked monocyte infiltration, NF-kappaB activation, and upregulation of NF-kappaB-related proinflammatory genes. Therefore, AT(1) and AT(2) blockade is necessary to arrest completely the inflammatory process. Treatment with two different NF-kappaB inhibitors, pirrolidin-dithiocarbamate and parthenolide, diminished monocyte infiltration and gene overexpression. These data show that Ang II, via AT(1) and AT(2) receptors and NF-kappaB pathway, participates in the regulation of renal monocyte recruitment and may provide a rationale to investigate further the role of AT(2) in human kidney diseases.

Systemic Infusion of Angiotensin II into Normal Rats Activates Nuclear Factor-κB and AP-1 in the Kidney : Role of AT1 and AT2 Receptors

Recent studies have pointed out the implication of angiotensin II (Ang II) in various pathological settings. However, the molecular mechanisms and the AngII receptor (AT) subtypes involved are not fully identified. We investigated whether AngII elicited the in vivo activation of nuclear transcription factors that play important roles in the pathogenesis of renal and vascular injury. Systemic infusion of Ang II into normal rats increased renal nuclear factor (NF)-kappaB and AP-1 binding activity that was associated with inflammatory cell infiltration and tubular damage. Interestingly, infiltrating cells presented activated NF-kappaB complexes, suggesting the involvement of AngII in inflammatory cell activation. When rats were treated with AT(1) or AT(2) receptor antagonists different responses were observed. The AT(1) antagonist diminished NF-kappaB activity in glomerular and tubular cells and abolished AP-1 in renal cells, improved tubular damage and normalized the arterial blood pressure. The AT(2) antagonist diminished mononuclear cell infiltration and NF-kappaB activity in glomerular and inflammatory cells, without any effect on AP-1 and blood pressure. These data suggest that AT(1) mainly mediates tubular injury via AP-1/NF-kappaB, whereas AT(2) receptor participates in the inflammatory cell infiltration in the kidney by NF-kappaB. Our results provide novel information on AngII receptor signaling and support the recent view of Ang II as a proinflammatory modulator.

Activation of the Endosome-Associated Ubiquitin Isopeptidase AMSH by STAM, a Component of the Multivesicular Body-Sorting Machinery

AMSH is an endosomal ubiquitin isopeptidase that can limit EGF receptor downregulation . It directly binds to the SH3 domain of STAM, which is constitutively associated with Hrs, a component of clathrin-coated structures on endosomes. This clathrin coat has been implicated in the recruitment of ubiquitinated growth factor receptors prior to their incorporation into internal vesicles of the multivesicular body (MVB) , through the concerted action of ESCRT complexes I, II, and III . We now show that AMSH is embedded within a network of interactions with components of the MVB-sorting machinery. AMSH and STAM, like Hrs , both bind directly to clathrin. AMSH also interacts with mVps24/CHMP3, a component of ESCRT III complex, and this interaction is reinforced through simultaneous STAM binding. We have explored the effect of interacting components on the in vitro enzymatic activity of AMSH. The enzyme shows specificity for K63- over K48-linked polyubiquitin chains in vitro and is markedly stimulated by coincubation with STAM, indicating that activation of AMSH is coupled to its association with the MVB-sorting machinery. Other interacting factors do not directly stimulate AMSH but may serve to orient the enzyme with respect to substrates on the endosomal membrane.

Phosphatidylinositol-5-Phosphate Activation and Conserved Substrate Specificity of the Myotubularin Phosphatidylinositol 3-Phosphatases

Phosphoinositides control many different processes required for normal cellular function. Myotubularins are a family of Phosphatidylinositol 3-phosphate (PtdIns3P) phosphatases identified by the positional cloning of the MTM1 gene in patients suffering from X-linked myotubular myopathy and the MTMR2 gene in patients suffering from the demyelinating neuropathy Charcot-Marie-Tooth disease type 4B. MTM1 is a phosphatidylinositol phosphatase with reported specificity toward PtdIns3P, while the related proteins MTMR2 and MTMR3 hydrolyze both PtdIns3P and PtdIns(3,5)P2. We have investigated MTM1 and MTMR6 and find that they use PtdIns(3,5)P2 in addition to PtdIns3P as a substrate in vitro. The product of PtdIns(3,5)P2 hydrolysis, PtdIns5P, causes MTM1 to form a heptameric ring that is 12.5 nm in diameter, and it is a specific allosteric activator of MTM1, MTMR3, and MTMR6. A disease-causing mutation at arginine 69 of MTM1 falling within a putative pleckstrin homology domain reduces the ability of the enzyme to respond to PtdIns5P. We propose that the myotubularin family of enzymes utilize both PtdIns3P and PtdIns(3,5)P2 as substrates, and that PtdIns5P functions in a positive feedback loop controlling their activity. These findings highlight the importance of regulated phosphatase activity for the control of phosphoinositide metabolism.

Angiotensin II Increases Connective Tissue Growth Factor in the Kidney

Connective tissue growth factor (CTGF) has been described as a novel fibrotic mediator. CTGF is overexpressed in several kidney diseases and is induced by different factors involved in renal injury. Angiotensin II (AngII) participates in the pathogenesis of kidney damage, contributing to fibrosis; however, whether AngII regulates CTGF in the kidney has not been explored. Systemic infusion of AngII into normal rats for 3 days increased renal CTGF mRNA and protein levels. At day 7, AngII-infused rats presented overexpression of CTGF in glomeruli, tubuli, and renal arteries, as well as tubular injury and elevated fibronectin deposition. Only treatment with an AT(1) receptor antagonist, but not an AT(2), diminished CTGF and fibronectin overexpression and ameliorated tubular damage. In rats with immune complex nephritis, renal overexpression of CTGF was diminished by the ACE inhibitor quinapril, correlated with a diminution in fibrosis. In cultured renal cells (mesangial and tubular epithelial cells) AngII, via AT(1), increased CTGF mRNA and protein production, and a CTGF antisense oligonucleotide decreased AngII-induced fibronectin synthesis. Our data show that AngII regulates CTGF in the kidney and cultured in mesangial and tubular cells. This novel finding suggests that CTGF could be a mediator of the profibrogenic effects of AngII in the kidney.

Angiotensin IV Activates the Nuclear Transcription Factor-κB and Related Proinflammatory Genes in Vascular Smooth Muscle Cells

Inflammation is a key event in the development of atherosclerosis. Nuclear factor-&kgr;B (NF-&kgr;B) is important in the inflammatory response regulation. The effector peptide of the renin angiotensin system Angiotensin II (Ang II) activates NF-&kgr;B and upregulates some related proinflammatory genes. Our aim was to investigate whether other angiotensin-related peptides, as the N-terminal degradation peptide Ang IV, could regulate proinflammatory factors (activation of NF-&kgr;B and related genes) in cultured vascular smooth muscle cells (VSMCs). In these cells, Ang IV increased NF-&kgr;B DNA binding activity, caused nuclear translocation of p50/p65 subunits, cytosolic I&kgr;B degradation and induced NF-&kgr;B–dependent gene transcription. Ang II activates NF-&kgr;B via AT1 and AT2 receptors, but AT1 or AT2 antagonists did not inhibit NF-&kgr;B activation caused by Ang IV. In VSMC from AT1a receptor knockout mice, Ang IV also activated NF-&kgr;B pathway. In those cells, the AT4 antagonist divalinal diminished dose-dependently Ang IV–induced NF-&kgr;B activation and prevented I&kgr;B degradation, but had no effect on the Ang II response, indicating that Ang IV activates the NF-&kgr;B pathway via AT4 receptors. Ang IV also increased the expression of proinflammatory factors under NF-&kgr;B control, such as MCP-1, IL-6, TNF-&agr;, ICAM-1, and PAI-1, which were blocked by the AT4 antagonist. Our results reveal that Ang IV, via AT4 receptors, activates NF-&kgr;B pathway and increases proinflammatory genes. These data indicate that Ang IV possesses proinflammatory properties, suggesting that this Ang degradation peptide could participate in the pathogenesis of cardiovascular diseases.

The Myotubularin Family of Lipid Phosphatases

The myotubularins (MTMs) constitute a large family of phosphoinositide lipid 3‐phosphatases with specificity for PtdIns3P and PtdIns (3,5)P2. Mutations in MTM proteins are associated with inherited conditions such as myotubular myopathy and Charcot–Marie–Tooth syndrome. The substrate lipids are known to be regulators of the endosomal pathway through recruitment of specific effector proteins. Hydrolysis of PtdIns (3,5)P2 provides a biosynthetic pathway to the production of PtdIns5P, which itself can allosterically activate MTMs. We review the properties of this intriguing family of proteins and discuss potential physiological functions that include regulation of the endocytic pathway.