Aberrant Epigenetic Silencing Is Triggered by a Transient Reduction in Gene Expression

Aberrant epigenetic silencing plays a major role in cancer formation by inactivating tumor suppressor genes. While the endpoints of aberrant silencing are known, i.e., promoter region DNA methylation and altered histone modifications, the triggers of silencing are not known. We used the tet-off system to test the hypothesis that a transient reduction in gene expression will sensitize a promoter to undergo epigenetic silencing.The tet responsive promoter (P(TRE)) was used to drive expression of the selectable human HPRT cDNA in independent transfectants of an Hprt deficient mouse cell line. In this system, high basal HPRT expression is greatly reduced when doxycycline (Dox) is added to the culture medium. Exposure of the P(TRE)-HPRT transfectants to Dox induced HPRT deficient clones in a time dependent manner. A molecular analysis demonstrated promoter region DNA methylation, loss of histone modifications associated with expression (i.e., H3 lysine 9 and 14 acetylation and lysine 4 methylation), and acquisition of the repressive histone modification H3 lysine 9 methylation. These changes, which are consistent with aberrant epigenetic silencing, were not present in the Dox-treated cultures, with the exception of reduced H3 lysine 14 acetylation. Silenced alleles readily reactivated spontaneously or after treatment of cells with inhibitors of histone deacetylation and/or DNA methylation, but re-silencing of reactivated alleles did not require a new round of Dox exposure. Inhibition of histone deacetylation inhibited both the induction of silencing and re-silencing, whereas inhibition of DNA methylation had no such effect.This study demonstrates that a transient reduction in gene expression triggers a pathway for aberrant silencing in mammalian cells and identifies histone deacetylation as a critical early step in this process. DNA methylation, in contrast, is a secondary step in the silencing pathway under study. A model to explain these observations is offered

Wykorzystanie powłok TiN jako zmodyfikowanych powierzchni kontaktowych w implantowalnej rotacyjnej komorze wspomagania serca ReligaHeart ROT

Constructions of the mechanical-bearingless centrifugal blood pumps utilize different types of non-contact physical bearings, which allows to balance the forces that have an impact on the pump impeller, stabilizing its position in the pump house without wall contact. The paper presents investigations of the hybrid (passive magnetic bearings and hydrodynamic bearings) suspension system for the centrifugal blood pump. Numerical simulations were used to evaluate the hydrodynamic bearing lifting force and magnetic bearing forces interaction. An important aspect of rotor suspension system design was the nominal gap in hydrodynamic bearing area in order to reduce the blood damage risk in this region. The analyses results confirmed that for a small diameter centrifugal pump, the nominal operating hydrodynamic bearing gap could be established within the range from 0.033 to 0.072 mm.Konstrukcje pomp odśrodkowych pozbawionych łożysk mechanicznych wykorzystują różne rodzaje bezkontaktowych łożysk fizycznych, które pozwalają balansować siły oddziałujące na wirnik pompy, stabilizując jego pozycję w obudowie pompy bez kontaktu ze ścianami. Artykuł przedstawia badania hybrydowego (pasywne łożyska magnetyczne i łożyska hydrodynamiczne) systemu zawieszenia wirnika dla odśrodkowej pompy krwi. Symulacji numerycznych użyto dla zbadania siły unoszącej łożyska hydrodynamicznego oraz reakcji łożysk magnetycznych. Ważnym aspektem konstrukcji systemu zawieszenia wirnika było zwiększenie nominalnego prześwitu w obszarze łożyska hydrodynamicznego, aby zredukować ryzyko uszkadzania krwi w tym rejonie. Wyniki analiz potwierdziły możliwość wyznaczenia nominalnego prześwitu w łożysku hydrodynamicznym, dla pomp odśrodkowych małej średnicy, w przedziale od 0,033 do 0,072 mm

Noninvasive acoustic blood volume measurement system for the POLVAD prosthesis

The following paper presents researches concerning a noninvasive real-time blood volume measurement system applied in POLVAD prosthesis. The system is based on the acoustic Helmholtz resonator principle. The basis of the measurement method, followed by the preliminary tests of the possibility of incorporating the Helmholtz resonance idea into the POLVAD prosthesis is shown. The paper includes the actual measurement system construction and test results, both static and dynamic obtained at the Foundation for Cardiac Surgery Development in Zabrze, Poland. Conclusions and future plans are presented too