Emilio Hirsch

Blockade of PI3Kgamma suppresses joint inflammation and damage in mouse models of rheumatoid arthritis

Phosphoinositide 3-kinases (PI3K) have long been considered promising drug targets for the treatment of inflammatory and autoimmune disorders as well as cancer and cardiovascular diseases. But the lack of specificity, isoform selectivity and poor biopharmaceutical profile of PI3K inhibitors have so far hampered rigorous disease-relevant target validation. Here we describe the identification and development of specific, selective and orally active small-molecule inhibitors of PI3Kγ (encoded by Pik3cg). We show that Pik3cg−/− mice are largely protected in mouse models of rheumatoid arthritis; this protection correlates with defective neutrophil migration, further validating PI3Kγ as a therapeutic target. We also describe that oral treatment with a PI3Kγ inhibitor suppresses the progression of joint inflammation and damage in two distinct mouse models of rheumatoid arthritis, reproducing the protective effects shown by Pik3cg−/− mice. Our results identify selective PI3Kγ inhibitors as potential therapeutic molecules for the treatment of chronic inflammatory disorders such as rheumatoid arthritis.

Non-redundant role of the long pentraxin PTX3 in anti-fungal innate immune response

Pentraxins are a superfamily of conserved proteins that are characterized by a cyclic multimeric structure. The classical short pentraxins, C-reactive protein (CRP) and serum amyloid P component (SAP), are acute-phase proteins produced in the liver in response to inflammatory mediators. Short pentraxins regulate innate resistance to microbes and the scavenging of cellular debris and extracellular matrix components. In contrast, long pentraxins have an unrelated, long amino-terminal domain coupled to the carboxy-terminal pentraxin domain, and differ, with respect to short pentraxins, in their gene organization, chromosomal localization, cellular source, and in their stimuli-inducing and ligand-recognition ability. To investigate the in vivo function of the long pentraxin PTX3, we generated mice deficient in Ptx3 by homologous recombination. Ptx3-null mice were susceptible to invasive pulmonary aspergillosis. Ptx3 binds selected microbial agents, including conidia of Aspergillus fumigatus, and we found that susceptibility of Ptx3-null mice was associated with defective recognition of conidia by alveolar macrophages and dendritic cells, as well as inappropriate induction of an adaptive type 2 response. Thus, the long pentraxin Ptx3 is a secreted pattern-recognition receptor that has a non-redundant role in resistance to selected microbial agents, in particular to the opportunistic fungal pathogen Aspergillus fumigatus.

Regulation of Myocardial Contractility and Cell Size by Distinct PI3K-PTEN Signaling Pathways

The PTEN/PI3K signaling pathway regulates a vast array of fundamental cellular responses. We show that cardiomyocyte-specific inactivation of tumor suppressor PTEN results in hypertrophy, and unexpectedly, a dramatic decrease in cardiac contractility. Analysis of double-mutant mice revealed that the cardiac hypertrophy and the contractility defects could be genetically uncoupled. PI3Kalpha mediates the alteration in cell size while PI3Kgamma acts as a negative regulator of cardiac contractility. Mechanistically, PI3Kgamma inhibits cAMP production and hypercontractility can be reverted by blocking cAMP function. These data show that PTEN has an important in vivo role in cardiomyocyte hypertrophy and GPCR signaling and identify a function for the PTEN-PI3Kgamma pathway in the modulation of heart muscle contractility.

PI3Kγ Modulates the Cardiac Response to Chronic Pressure Overload by Distinct Kinase-Dependent and -Independent Effects

The G protein-coupled, receptor-activated phosphoinositide 3-kinase gamma (PI3Kgamma) mediates inflammatory responses and negatively controls cardiac contractility by reducing cAMP concentration. Here, we report that mice carrying a targeted mutation in the PI3Kgamma gene causing loss of kinase activity (PI3KgammaKD/KD) display reduced inflammatory reactions but no alterations in cardiac contractility. We show that, in PI3KgammaKD/KD hearts, cAMP levels are normal and that PI3Kgamma-deficient mice but not PI3KgammaKD/KD mice develop dramatic myocardial damage after chronic pressure overload induced by transverse aortic constriction (TAC). Finally, our data indicate that PI3Kgamma is an essential component of a complex controlling PDE3B phosphodiesterase-mediated cAMP destruction. Thus, cardiac PI3Kgamma participates in two distinct signaling pathways: a kinase-dependent activity that controls PKB/Akt as well as MAPK phosphorylation and contributes to TAC-induced cardiac remodeling, and a kinase-independent activity that relies on protein interactions to regulate PDE3B activity and negatively modulates cardiac contractility.

PTX3 plays a key role in the organization of the cumulus oophorus extracellular matrix and in in vivo fertilization

PTX3 is a prototypic long pentraxin that plays a non-redundant role in innate immunity against selected pathogens and in female fertility. Here, we report that the infertility of Ptx3–/– mice is associated with severe abnormalities of the cumulus oophorus and failure of in vivo, but not in vitro, oocyte fertilization. PTX3 is produced by mouse cumulus cells during cumulus expansion and localizes in the matrix. PTX3 is expressed in the human cumulus oophorus as well. Cumuli from Ptx3–/– mice synthesize normal amounts of hyaluronan (HA), but are unable to organize it in a stable matrix. Exogenous PTX3 restores a normal cumulus phenotype. Incorporation in the matrix of inter-α-trypsin inhibitor is normal in Ptx3–/– cumuli. PTX3 does not interact directly with HA, but it binds the cumulus matrix hyaladherin tumor necrosis factor α-induced protein 6 (TNFAIP6, also known as TSG6) and thereby may form multimolecular complexes that can cross-link HA chains. Thus, PTX3 is a structural constituent of the cumulus oophorus extracellular matrix essential for female fertility.

Phosphoinositide 3-Kinase γ Is an Essential Amplifier of Mast Cell Function

Abstract Mast cells are key regulators in allergy and inflammation, and release histamine upon clustering of their IgE receptors. Here we demonstrate that murine mast cell responses are exacerbated in vitro and in vivo by autocrine signals through G protein-coupled receptors (GPCRs) and require functional phosphoinositide 3-kinase γ (PI3Kγ). Adenosine, acting through the A 3 adenosine receptor (A 3 AR) as well as other agonists of G αi -coupled GPCRs, transiently increased PtdIns(3,4,5) P 3 exclusively via PI3Kγ. PI3Kγ-derived PtdIns(3,4,5) P 3 was instrumental for initiating a sustained influx of external Ca 2+ and degranulation. Mice lacking PI3Kγ did not form edema after intradermal injection of adenosine and when challenged by passive systemic anaphylaxis. PI3Kγ thus relays inflammatory signals through various G i -coupled receptors and is central to mast cell function.

Melusin, a muscle-specific integrin β1-interacting protein, is required to prevent cardiac failure in response to chronic pressure overload

Cardiac hypertrophy is an adaptive response to a variety of mechanical and hormonal stimuli, and represents an early event in the clinical course leading to heart failure. By gene inactivation, we demonstrate here a crucial role of melusin, a muscle-specific protein that interacts with the integrin β1 cytoplasmic domain, in the hypertrophic response to mechanical overload. Melusin-null mice showed normal cardiac structure and function in physiological conditions, but when subjected to pressure overload—a condition that induces a hypertrophic response in wild-type controls—they developed an abnormal cardiac remodeling that evolved into dilated cardiomyopathy and contractile dysfunction. In contrast, the hypertrophic response was identical in wild-type and melusin-null mice after chronic administration of angiotensin II or phenylephrine at doses that do not increase blood pressure—that is, in the absence of cardiac biomechanical stress. Analysis of intracellular signaling events induced by pressure overload indicated that phosphorylation of glycogen synthase kinase-3β (GSK-3β) was specifically blunted in melusin-null hearts. Thus, melusin prevents cardiac dilation during chronic pressure overload by specifically sensing mechanical stress.

Cardiovascular side effects of cancer therapies: a position statement from the Heart Failure Association of the European Society of Cardiology

The reductions in mortality and morbidity being achieved among cancer patients with current therapies represent a major achievement. However, given their mechanisms of action, many anti‐cancer agents may have significant potential for cardiovascular side effects, including the induction of heart failure. The magnitude of this problem remains unclear and is not readily apparent from current clinical trials of emerging targeted agents, which generally under‐represent older patients and those with significant co‐morbidities. The risk of adverse events may also increase when novel agents, which frequently modulate survival pathways, are used in combination with each other or with other conventional cytotoxic chemotherapeutics. The extent to which survival and growth pathways in the tumour cell (which we seek to inhibit) coincide with those in cardiovascular cells (which we seek to preserve) is an open question but one that will become ever more important with the development of new cancer therapies that target intracellular signalling pathways. It remains unclear whether potential cardiovascular problems can be predicted from analyses of such basic signalling mechanisms and what pre‐clinical evaluation should be undertaken. The screening of patients, optimization of therapeutic schemes, monitoring of cardiovascular function during treatment, and the management of cardiovascular side effects are likely to become increasingly important in cancer patients. This paper summarizes the deliberations of a cross‐disciplinary workshop organized by the Heart Failure Association of the European Society of Cardiology (held in Brussels in May 2009), which brought together clinicians working in cardiology and oncology and those involved in basic, translational, and pharmaceutical science.

Inflammation as a therapeutic target in heart failure? A scientific statement from the Translational Research Committee of the Heart Failure Association of the European Society of Cardiology

The increasing prevalence of heart failure poses enormous challenges for health care systems worldwide. Despite effective medical interventions that target neurohumoral activation, mortality and morbidity remain substantial. Evidence for inflammatory activation as an important pathway in disease progression in chronic heart failure has emerged in the last two decades. However, clinical trials of ‘anti‐inflammatory’ therapies (such as anti‐tumor necrosis factor‐α approaches) have to date failed to show benefit in heart failure patients. The Heart Failure Association of the European Society of Cardiology recently organized an expert workshop to address the issue of inflammation in heart failure from a basic science, translational and clinical perspective, and to assess whether specific inflammatory pathways may yet serve as novel therapeutic targets for this condition. This consensus document represents the outcome of the workshop and defines key research questions that still need to be addressed as well as considering the requirements for future clinical trials in this area.

Phosphoinositide 3-kinase p110beta activity : key role in metabolism and mammary gland cancer but not development

The phosphoinositide 3-kinase p110β subunit has noncatalytic functions; its catalytic activity is pertinent to both diabetes and cancer. Unveiling p110β Phosphatidylinositide 3-kinase (PI3K) signaling has been implicated in the response to insulin and various growth factors. However, the specific role of the β isoform of the PI3K catalytic subunit (p110β) has been unclear. Analysis of mouse mutants carrying a catalytically inactive form of p110β reveals that it possesses noncatalytic as well as catalytic functions. Moreover, its catalytic activity is involved in sustaining the response to insulin signaling and in mediating forms of breast cancer associated with oncogenic epidermal growth factor signaling. The phosphoinositide 3-kinase (PI3K) pathway crucially controls metabolism and cell growth. Although different PI3K catalytic subunits are known to play distinct roles, the specific in vivo function of p110β (the product of the PIK3CB gene) is not clear. Here, we show that mouse mutants expressing a catalytically inactive PIK3CBK805R mutant survived to adulthood but showed growth retardation and developed mild insulin resistance with age. Pharmacological and genetic analyses of p110β function revealed that p110β catalytic activity is required for PI3K signaling downstream of heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors as well as to sustain long-term insulin signaling. In addition, PIK3CBK805R mice were protected in a model of ERBB2-driven tumor development. These findings indicate an unexpected role for p110β catalytic activity in diabetes and cancer, opening potential avenues for therapeutic intervention.