PKA phosphorylation in HF Flashcards
The role of PKA hyperphosphorylation in HF was first brought to the attention by who?
Marks et al 2001
Marks et al 2001
Using a planar bilipid system, they studied the effects of PKA addition to the RyR channel. They described that this increased the open probability of the channel at the S2808 position.
They then examined failing hearts from canine and rat models, and they found that the PKA phosphorylationin the failing hearts was about 4x more than non-failing hearts at this S2808.
The increase in open probability, by adding a serine, to the S2808 to decrease its ability to be phosphorylated caused a reduction of the RyR open probability.
Using co-sedimentation and co-immunoprecipitation they then identified a complex of RyR2, MAKAP activating protein, Calstabin, PKA and phosphatases. They then noticed that the hyperphosphorylation was due to a reduction in phosphatases on the RyR. They also identified, that when this occurs, it leads to a dissociation of the calstabin binding unit. They postulated that this lead to the increased calcium leak during diastole which would lead to reduction in contractility in HF.
What was the complex found by Marks et al 2001
Using co-sedimentation and co-immunoprecipitation they then identified a complex of RyR2, MAKAP activating protein, Calstabin, PKA and phosphatases
Using co-sedimentation and co-immunoprecipitation they then identified a complex of RyR2, MAKAP activating protein, Calstabin, PKA and phosphatases. They then noticed that the hyperphosphorylation was due to a reduction in phosphatases on the RyR. They also identified, that when this occurs, it leads to a dissociation of the calstabin binding unit. They postulated that this lead to the increased calcium leak during diastole which would lead to reduction in contractility in HF.
Marks et 2001
Stange et al 2001
Although the findings from Marks et al study were promising, they did not find the increase in open probability of the RyR
Morimoto et al 2009
Isolated papillary muscles and trabeculae from mice with LV hypertrophy and pretreated them with isoprotenerol (b agonist) and then sapin permeabilised them.
Using caffeine to induce SR leak, what their study showed was that there was increased SR leak when PKA was hyperphosphorylated as measured with Fluo-3. This increased leak was blocked with a PKA blocker, H89.
Wehrens et al 2006
They generated S2808A mice and compared the findings with WT mice. They induced MI directly by the ligation of the LAD. They then looked at the echocardiogram 28 days later and demonstrated that in the S2808A mouse, there was increase in contractility and PEF, and they were protected from the negative remodelling associated with the MI compared to WT
Controversy
The house of Valdiva 2007 and 2017
Valdiva et 2017
Generated S2808A mice, and induced aortic banding to induce a pressure-overloaded HF. They they identidfied that unlike Wehrens et al’s mice, there was equal hypertrophy and systolic dysfunction in both the WT mice and the S2808A mice. This suggested that the PKA was not protective, from the MI as they suggested
Valdiva et al 2017
As the mice used in Wehrens study had different genetic background, different from the mice used by Valdiva et al in 2007 involving a mixed background, which could account for the difference in results, they then used the same strain of mice. Once again, their group was unable to find any protective measure conferred to the mice by S2808A
Reasons for the difference
This is an ongoing and controversial topic in the scientific world, with various studies having different results. Now we will discuss some of the reasons for this.
- Different models - Aortic banding vs LAD by Wehrens
- Diurnal variation - Gamble et al 2009 suggest that diurnal variation via the circadian rhythm, in the expression of genes can regulate the pathological phenotype of RYR
- Reagents and interpretation of results used could also be different
- The oxidation states of the RyR channel is an established one, and this could lead to the variation in findings
- Developmental issues. In 2011 Shan et al developed S2808D mice and they found that although RyR was hyperactive, in the neonates, the calstabin binding was still present, but in the adult mice > 6 months and older, the calstabin was absent.
Gamble et al 2009 suggest
Diurnal variation - Gamble et al 2009 suggest that diurnal variation via the circadian rhythm, in the expression of genes can regulate the pathological phenotype of RYR
Shan et al 2011
S2808D mice and they found that although RyR was hyperactive, in the neonates, the calstabin binding was still present, but in the adult mice > 6 months and older, the calstabin was absent.
Bers et al 2012
Maybe PKA hyperphosphorylation might not be the only contributor to the mechanism of HF, they suggest that CAMKII activity might in fact also play a role in RyR hyperphosphorylation, and Wehrens et al 2004 identify that these two have separate binding sites on the RyR with no competition.
