H017 Time dependent activation of AKT-GSK3beta and calcineurin signaling pathways during the development of TAC-induced left ventricular hypertrophy in B6D2/F1 mice

Abstract

Left ventricular hypertrophy (LVH) is an adaptive response to chronic biomechanical stress that later progresses to maladaptive hypertrophy and heart failure. To better understand the mechanisms responsible for LVH development, we studied the activation of two major kinases, protein kinase B (Akt/PKB) and glycogen synthase kinase3b (GSK3b) and of a phosphatase, calcineurin (Cn) in an experimental model of thoracic aorta constriction (TAC). 4 week-old B6D2/F1 male, Sham-operated (Sham) and TAC mice were studied 3, 7, 15, 30 and 60 days post-TAC. Gene expression and activation of signalling pathways was studied by PCR and Western Blot. TAC-induced LVH (10 – 51 % at days 3-60, respectively) was associated with: 1) fetal gene reexpression characterised by an increase in mRNA levels of BNP (1.7-3 fold) and a-SK (2-4 fold), an a- to b-MHC switch seen at day 30 only ; 2) a significant increase in SERCA2a (1.7 fold), PLB, and NCX (3.6 fold) protein levels at day 7. 3) a 2 fold increase in P-Akt at day 3 and a decrease at day 15 while Akt was increased at days 7 and 15 ; 4) an increase in P-GSK3b at day 15 (1.5 fold), whereas no change in Akt and GSK3b protein levels were seen at days 30 and 60 ; 5) a significant decrease in CnAb at day 15 (2 fold). LVH develops progressively from day 3 in response to TAC, accompanied by re-expression of the fetal gene program. The alpha to beta-MHC mRNA switch occurs late, associated with the transition to HF, which occurs progressively with time. At days 3 and 15, P-Akt acts as an upstream regulator of GSK3b which may favour the development of LVH. 7 days post-TAC, a SERCA2a and NCX increase might contribute to decrease free cytosolic calcium level. At day 15, a further increase in LVH is associated with an increase in Cn activity and an increase GSK3b, which may counteract the hypertrophic response. Taken together, our data suggest a time-dependent cross-talk between Cn and GSK3b to modulate cardiac hypertrophic response to pressure overload.