Cell-specific expression of fibronectin and EIIIA and EIIIB splice variants after oxygen injury

Oxidative stress diseases unique to the perinatal period: A window into the developing innate immune response

The innate immune system has evolved to play an integral role in the normally developing lung and brain. However, in response to oxidative stress, innate immunity, mediated by specific cellular and molecular programs and signaling, contributes to pathology in these same organ systems. Despite opposing drivers of oxidative stress, namely hyperoxia in neonatal lung injury and hypoxia/ischemia in neonatal brain injury, similar pathways-including toll-like receptors, NFκB and MAPK cascades-have been implicated in tissue damage. In this review, we consider recent insights into the innate immune response to oxidative stress in both neonatal and adult models to better understand hyperoxic lung injury and hypoxic-ischemic brain injury across development and aging. These insights support the development of targeted immunotherapeutic strategies to address the challenge of harnessing the innate immune system in oxidative stress diseases of the neonate.

Plasma and cellular fibronectin: distinct and independent functions during tissue repair

Fibronectin (FN) is a ubiquitous extracellular matrix (ECM) glycoprotein that plays vital roles during tissue repair. The plasma form of FN circulates in the blood, and upon tissue injury, is incorporated into fibrin clots to exert effects on platelet function and to mediate hemostasis. Cellular FN is then synthesized and assembled by cells as they migrate into the clot to reconstitute damaged tissue. The assembly of FN into a complex three-dimensional matrix during physiological repair plays a key role not only as a structural scaffold, but also as a regulator of cell function during this stage of tissue repair. FN fibrillogenesis is a complex, stepwise process that is strictly regulated by a multitude of factors. During fibrosis, there is excessive deposition of ECM, of which FN is one of the major components. Aberrant FN-matrix assembly is a major contributing factor to the switch from normal tissue repair to misregulated fibrosis. Understanding the mechanisms involved in FN assembly and how these interplay with cellular, fibrotic and immune responses may reveal targets for the future development of therapies to regulate aberrant tissue-repair processes.

Alveolar type II cells from ethanol-fed rats produce a fibronectin-enriched extracellular matrix that promotes monocyte activation

Acute lung injury affects close to 200,000 people in the United States annually and leads to death in 40-50% of the affected patients. Chronic ethanol abuse is thought to contribute to up to 40-50% of subjects who develop acute lung injury. We previously demonstrated in a rat model that chronic ethanol ingestion promoted acute lung injury and associated with chronic oxidant stress, activated matrix metalloproteinases, increased release of transforming growth factor-beta, and increased expression and deposition of fibronectin, a matrix glycoprotein implicated in lung injury and repair. Because fibronectin can activate monocytes to increase pro-inflammatory cytokine expression, we hypothesized that generation of fibronectin-enriched matrices during chronic ethanol ingestion might contribute to the development of acute lung injury by stimulating unopposed inflammation. To test this hypothesis, we harvested alveolar type II cells from rats fed the Lieber-DeCarli diet (6 weeks; 36% of calories from ethanol). After 96h of culture, the matrices deposited ex vivo by the type II cells derived from ethanol-fed rats showed increased amounts of fibronectin protein as demonstrated by ELISA. When monocytic U937 cells were plated atop these matrices, there was increased expression of interleukin-1beta (IL-1beta). This stimulation was inhibited by antibodies against alpha5beta1, a receptor that mediates many of the biological effects of fibronectin. We then tested whether antioxidants ameliorated these effects. Dietary supplements of the antioxidants N-acetylcysteine and procysteine normalized matrix production by type II cells. Furthermore, the newly derived matrices did not stimulate IL-1beta expression over control cells. These studies suggest that chronic ethanol exposure induces oxidant stress and activates lung tissue remodeling characterized by increased expression of fibronectin by alveolar type II cells. The newly deposited fibronectin-enriched matrices may stimulate the expression of pro-inflammatory cytokines in monocytic cells recruited to the lung after injury thereby explaining the priming effects of ethanol.