RESUMEN

Pulmonary fibrosis is a common and dose-limiting side-effect of ionizing radiation used to treat cancers of the thoracic region. Few effective therapies are available for this disease. Pulmonary fibrosis is characterized by an accumulation of myofibroblasts and excess deposition of extracellular matrix proteins. Although prior studies have reported that ionizing radiation induces fibroblast to myofibroblast differentiation and collagen production, the mechanism remains unclear. Transforming growth factor-ß (TGF-ß) is a key profibrotic cytokine that drives myofibroblast differentiation and extracellular matrix production. However, its activation and precise role in radiation-induced fibrosis are poorly understood. Recently, we reported that lactate activates latent TGF-ß through a pH-dependent mechanism. Here, we wanted to test the hypothesis that ionizing radiation leads to excessive lactate production via expression of the enzyme lactate dehydrogenase-A (LDHA) to promote myofibroblast differentiation. We found that LDHA expression is increased in human and animal lung tissue exposed to ionizing radiation. We demonstrate that ionizing radiation induces LDHA, lactate production, and extracellular acidification in primary human lung fibroblasts in a dose-dependent manner. We also demonstrate that genetic and pharmacologic inhibition of LDHA protects against radiation-induced myofibroblast differentiation. Furthermore, LDHA inhibition protects from radiation-induced activation of TGF-ß. We propose a profibrotic feed forward loop, in which radiation induces LDHA expression and lactate production, which can lead to further activation of TGF-ß to drive the fibrotic process. These studies support the concept of LDHA as an important therapeutic target in radiation-induced pulmonary fibrosis.

Asunto(s)

L-Lactato Deshidrogenasa/metabolismo , Miofibroblastos/efectos de la radiación , Animales , Diferenciación Celular/efectos de la radiación , Células Cultivadas , Inhibidores Enzimáticos/farmacología , Gosipol/farmacología , Humanos , Isoenzimas/antagonistas & inhibidores , Isoenzimas/metabolismo , L-Lactato Deshidrogenasa/antagonistas & inhibidores , Lactato Deshidrogenasa 5 , Ácido Láctico/biosíntesis , Pulmón/enzimología , Pulmón/efectos de la radiación , Ratones , Ratones Endogámicos C57BL , Modelos Biológicos , Miofibroblastos/citología , Miofibroblastos/enzimología , Fibrosis Pulmonar/enzimología , Fibrosis Pulmonar/etiología , Traumatismos por Radiación/enzimología , Traumatismos por Radiación/etiología , Factor de Crecimiento Transformador beta/metabolismo

RESUMEN

A critical component of corneal scarring is the TGFß-induced differentiation of corneal keratocytes into myofibroblasts. Inhibitors of this differentiation are potentially therapeutic for corneal scarring. In this study, we tested the relative effectiveness and mechanisms of action of two electrophilic peroxisome proliferator-activated receptor gamma (PPARγ) ligands: cyano-3,12-dioxolean-1,9-dien-28-oic acid-methyl ester (CDDO-Me) and 15-deoxy-Δ(-12,14)-prostaglandin J(2) (15d-PGJ(2)) for inhibiting TGFß-induced myofibroblast differentiation in vitro. TGFß was used to induce myofibroblast differentiation in cultured, primary human corneal fibroblasts. CDDO-Me and 15d-PGJ(2) were added to cultures to test their ability to inhibit this process. Myofibroblast differentiation was assessed by measuring the expression of myofibroblast-specific proteins (αSMA, collagen I, and fibronectin) and mRNA (αSMA and collagen III). The role of PPARγ in the inhibition of myofibroblast differentiation by these agents was tested in genetically and pharmacologically manipulated cells. Finally, we assayed the importance of electrophilicity in the actions of these agents on TGFß-induced αSMA expression via Western blotting and immunofluorescence. Both electrophilic PPARγ ligands (CDDO-Me and 15d-PGJ(2)) potently inhibited TGFß-induced myofibroblast differentiation, but PPARγ was only partially required for inhibition of myofibroblast differentiation by either agent. Electrophilic PPARγ ligands were able to inhibit myofibroblast differentiation more potently than non-electrophilic PPARγ ligands, suggesting an important role of electrophilicity in this process. CDDO-Me and 15d-PGJ(2) are strong inhibitors of TGFß-induced corneal fibroblast to myofibroblast differentiation in vitro, suggesting this class of agents as potential novel therapies for corneal scarring warranting further study in pre-clinical animal models.

Asunto(s)

Transdiferenciación Celular/efectos de los fármacos , Córnea/citología , Fibroblastos/citología , Miofibroblastos/citología , Ácido Oleanólico/análogos & derivados , PPAR gamma/metabolismo , Prostaglandina D2/análogos & derivados , Actinas/genética , Actinas/metabolismo , Biomarcadores/metabolismo , Western Blotting , Células Cultivadas , Colágeno Tipo I/genética , Colágeno Tipo I/metabolismo , Córnea/metabolismo , Fibroblastos/metabolismo , Fibronectinas/genética , Fibronectinas/metabolismo , Citometría de Flujo , Técnica del Anticuerpo Fluorescente Indirecta , Humanos , Ligandos , Miofibroblastos/metabolismo , Ácido Oleanólico/farmacología , Prostaglandina D2/farmacología , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Factor de Crecimiento Transformador beta/farmacología

RESUMEN

The use of targeted cancer therapies in combination with conventional chemotherapeutic agents and/or radiation treatment has increased overall survival of cancer patients. However, longer survival is accompanied by increased incidence of comorbidities due, in part, to drug side effects and toxicities. It is well accepted that inflammation and tumorigenesis are linked. Because peroxisome proliferator-activated receptor (PPAR)-gamma agonists are potent mediators of anti-inflammatory responses, it was a logical extension to examine the role of PPARgamma agonists in the treatment and prevention of cancer. This paper has two objectives: first to highlight the potential uses for PPARgamma agonists in anticancer therapy with special emphasis on their role when used as adjuvant or combined therapy in the treatment of hematological malignancies found in the vasculature, marrow, and eyes, and second, to review the potential role PPARgamma and/or its ligands may have in modulating cancer-associated angiogenesis and tumor-stromal microenvironment crosstalk in bone marrow.