Paradoxical Role of AT-rich Interactive Domain 1A in Restraining Pancreatic Carcinogenesis

Background & Aims: ARID1A is postulated to be a tumor suppressor gene owing to loss-of-function mutations in human pancreatic ductal adenocarcinomas (PDAC). However, its role in pancreatic pathogenesis is not clear despite recent studies using genetically engineered mouse (GEM) models. We aimed at further understanding of its direct functional role in PDAC, using a combination of GEM model and PDAC cell lines. Methods: Pancreas-specific mutant Arid1a-driven GEM model (Ptf1a-Cre; KrasG12D; Arid1af/f or “KAC”) was generated by crossing Ptf1a-Cre; KrasG12D (“KC”) mice with Arid1af/f mice and characterized histologically with timed necropsies. Arid1a was also deleted using CRISPR-Cas9 system in established human and murine PDAC cell lines to study the immediate effects of Arid1a loss in isogenic models. Cell lines with or without Arid1a expression were developed from respective autochthonous PDAC GEM models, compared functionally using various culture assays, and subjected to RNA-sequencing for comparative gene expression analysis. DNA damage repair was analyzed in cultured cells using immunofluorescence and COMET assay. Results: Retention of Arid1a is critical for early progression of mutant Kras-driven pre-malignant lesions into PDAC, as evident by lower Ki-67 and higher apoptosis staining in “KAC” as compared to “KC” mice. Enforced deletion of Arid1a in established PDAC cell lines caused suppression of cellular growth and migration, accompanied by compromised DNA damage repair. Despite early development of relatively indolent cystic precursor lesions called intraductal papillary mucinous neoplasms (IPMNs), a subset of “KAC” mice developed aggressive PDAC in later ages. PDAC cells obtained from older autochthonous “KAC” mice revealed various compensatory (“escaper”) mechanisms to overcome the growth suppressive effects of Arid1a loss. Conclusions: Arid1a is an essential survival gene whose loss impairs cellular growth, and thus, its expression is critical during early stages of pancreatic tumorigenesis in mouse models. In tumors that arise in the setting of ARID1A loss, a multitude of “escaper” mechanisms drive progression

Measurements and Modeling of Reynolds Stress and Turbulence Production in a Swirl-Supported, Direct-Injection Diesel Engine

Measured and numerically predicted components of the mean rate-of-strain tensor _Sij_ and the Reynolds stress _u_ru___ are examined and compared to elucidate the source and scrutinize the modeling of late-cycle turbulence production in swirl-supported, direct-injection diesel engines. The experiments are performed with combustion in the engine inhibited, to eliminate the complicating influence of heat release on turbulence generation and to reduce the problem to one more closely approximating constant-density turbulence. Both the measurements and the calculations indicate that the primary influence of the mean flow swirl on turbulence production is confined to two separate periods: (1) shortly after the end of injection and (2) in the late-cycle period, when large positive levels of _u_r,u___ are observed. Formation of the positive Reynolds stress coincides with the development of a negative radial gradient in mean angular momentum, indicating an unstable mean flow field. At this time, the measured velocity fluctuations show a large increase, approximately doubling in magnitude compared to fluctuations measured without fuel injection. Predicted velocity fluctuations, obtained via k-_ turbulence modeling, show a similar late-cycle increase, although the magnitude of the increase is not quantitatively captured. To evaluate its applicability during the period in which the unstable, negative radial gradient in angular momentum is present, the isotropic eddy viscosity hypothesis is examined. The Reynolds stress estimated from the measured _Sr__ using the eddy viscosity hypothesis is found to mimic the measured stress with reasonable accuracy, and the measured and calculated r-_ plane turbulence production terms are shown to have excellent qualitative and quantitative agreement. The quantitative agreement, however, appears largely providential, as the measured and predicted values of _Sr__ differ by a factor of 2. This discrepancy is compensated for by the underpredicted turbulent kinetic energy and seemingly high values of the dissipation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86744/1/Sick29.pd