Phosphatase and tensin homolog deleted on chromosome ten (PTEN) as a molecular target in lung epithelial wound repair and protection

The long-term goal of this study is to identify a potential innovative therapeutic target to prevent or treat Acute Respiratory Distress Syndrome (ARDS), a condition associated with systemic inflammation and characterized by extensive lung epithelial damage leading to protein enriched fluid influx into the lung alveolar space and compromised ventilation [1, 2]. The rapid progression of acute lung injury at the onset of ARDS is one of the reasons responsible for the high mortality of ARDS [3]. A variety of strategies to treat and manage ARDS has been extensively investigated. However, patient survival has not been improved. Based on the previous work of our laboratory and numerous studies that identify the cell survival phosphatidylinositol 3'-kinase (PI3K)/Akt pathway as a vital survival axis in the lung epithelium, we focused on this pathway as a molecular target to prevent lung epithelium dysfunction [4-6]. Phosphatase and Tensin homolog deleted on chromosome Ten (PTEN) is a phosphase that is known to be a negative regulator of the PI3K/Akt survival pathway by dephosphorylation of PI(3,4,5)P3 at the 3 position in the inositol ring thereby inactivating this second messenger [7, 8]. We have observed that PTEN is enriched in the lung epithelium and previously reported that activation of the PI3K/Akt pathway promotes lung epithelial cell survival during inflammatory stress [4]. Based on this, we hypothesized that inhibition of PTEN by specific PTEN inhibitors would be a rational therapeutic strategy to maintain normal lung epithelial cell function under stress conditions or promote repair after damage has occurred. Synthesis of a relatively new and specific PTEN inhibitor, bisperoxovanadium, was first reported in 2004 utilizing cell culture models [9]. Based on the relative precision of bisperoxovadadium and a related analog to inhibit PTEN in vitro, we chose to test these compounds in our initial studies. The data presented in this dissertation support that bisperoxovanadium compounds are relatively specific PTEN inhibitors in human lung epithelia. Further, we have provided evidence to support that PTEN is a valid molecular target to facilitate epithelial wound closure in lung epithelia using both a human lung epithelium cell line and primary human lung cell cultures. We consistently observed utilizing different models that PTEN inhibition in the lung parenchyma leads to activation of the Akt and MAPK pathways. In contract, to date we have not observed supporting evidence that the focal adhesion kinase pathwayis involved both in vitro and in vivo. Importantly, these 3 pathways have previously been identified as the major pathways affected distal to PTEN. We further contend that cell migration following PTEN inhibition accounts for the majority of wound closure enhancement whereas changes in cell proliferation do not appear to be as significant. Using an alternative in vivo model we also observed that pretreatment with the PTEN inhibitor, bpV(phen), protected the lung from oleic acid (OA) induced acute injury in mice and maintained physiological function in addition to reducing mortality. In comparison to our previous in vitro studies, this part of investigation suggests that PTEN has an important role in determining lung parenchymal susceptibility to injury. Based on these observations, we contend that bisperoxovanadium compounds could be considered as potential therapeutic agents to prevent or facilitate epithelial wound repair. Further, PTEN appears to play a central role in the lung parenchyma in response to injury. As a result, we also contend that PTEN should be further examined as an important molecular target in the context of pulmonary pathophysiology.