Mechanical ventilation is a valuable treatment regimen for respiratory failure. However, mechanical ventilation (especially with high tidal volumes) is implicated in the initiation and/or exacerbation of lung injury. Hence, it is important to understand how the cells that line the inner surface of the lung [alveolar epithelial cells (AECs)] sense cyclic stretching. Here, we tested the hypothesis that matrix molecules, via their interaction with surface receptors, transduce mechanical signals in AECs. We first determined that rat AECs secrete an extracellular matrix (ECM) rich in anastamosing fibers composed of the α3 laminin subunit, complexed with β1 and γ1 laminin subunits (i.e. laminin-6), and perlecan by a combination of immunofluorescence microscopy and immunoblotting analyses. The fibrous network exhibits isotropic expansion when exposed to cyclic stretching (30 cycles per minute, 10% strain). Moreover, this same stretching regimen activates mitogen-activated-protein kinase (MAPK) in AECs. Stretch-induced MAPK activation is not inhibited in AECs treated with antagonists to α3 or β1 integrin. However, MAPK activation is significantly reduced in cells treated with function-inhibiting antibodies against the α3 laminin subunit and dystroglycan, and when dystroglycan is knocked down in AECs using short hairpin RNA. In summary, our results support a novel mechanism by which laminin-6, via interaction with dystroglycan, transduces a mechanical signal initiated by stretching that subsequently activates the MAPK pathway in rat AECs. These results are the first to indicate a function for laminin-6. They also provide novel insight into the role of the pericellular environment in dictating the response of epithelial cells to mechanical stimulation and have broad implications for the pathophysiology of lung injury.

Recent discoveries indicate that disorders of protein folding and degradation play a particularly important role in the development of lung diseases and their associated complications. The overarching purpose of the National Heart, Lung, and Blood Institute workshop on "Malformed Protein Structure and Proteostasis in Lung Diseases" was to identify mechanistic and clinical research opportunities indicated by these recent discoveries in proteostasis science that will advance our molecular understanding of lung pathobiology and facilitate the development of new diagnostic and therapeutic strategies for the prevention and treatment of lung disease. The workshop's discussion focused on identifying gaps in scientific knowledge with respect to proteostasis and lung disease, discussing new research advances and opportunities in protein folding science, and highlighting novel technologies with potential therapeutic applications for diagnosis and treatment.

S U M M A R Y Two epithelial cell types cover the alveolar surface of the lung. Type II alveolar epithelial cells produce surfactant and, during development or following wounding, give rise to type I cells that are involved in gas exchange and alveolar fluid homeostasis. In culture, freshly isolated alveolar type II cells assume a more squamous (type I-like) appearance within 4 days after plating. They assemble numerous focal adhesions that associate with the actin cytoskeleton at the cell margins. These alveolar epithelial cells lose expression of type II cell markers including SP-C and after 4 days in culture express the type I cell marker T1a. Those cells that express T1a also deposit fibers of laminin-311 in their matrix. The latter appears to be related to their development of a type I phenotype because freshly isolated, primary type I cells also assemble laminin-311-rich fibers in vitro. A b1 integrin antibody antagonist inhibits the assembly of laminin-311 matrix fibers. Moreover, the formation of laminin fibers is dependent on the activity of the small GTPases and is perturbed by ML-7, a myosin light chain kinase inhibitor. In summary, our data indicate that assembly of laminin-311 fibers by lung epithelial cells is integrin and actin cytoskeleton dependent, and that these fibers are characteristic of type I alveolar cells. (J Histochem Cytochem 54:665 -672, 2006)

A third of lung recipients have pre-existing antibodies against non-human leukocyte self-antigens (nHAbs) present in the lung tissue. These nHAbs also form de novo in about 70% of patients within 3-years following transplantation. Both pre-existing and de novo nHAbs can cause murine lung allograft rejection. However, their role in human transplantation remains unclear. We report hyperacute rejection following right lung transplant in a recipient with pre-existing nHAbs. Recipient of left lung from the same donor had uneventful initial course but developed de novo nHAbs at three weeks leading to acute humoral rejection. Both were successfully treated with antibody-directed therapies.

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