GRK-2: A Potential Target for Therapeutic Drugs Treating Heart Failure

Zachary Gallagher

Chembio spotlight #1

Paper: Inhibition of G-protein-coupled Receptor Kinase 2 Prevents the Dysfunctional Cardiac Substrate Metabolism in Fatty Acid Synthase

http://www.jbc.org/content/291/6/2583

GRK-2: A potential target for therapeutic drugs treating Heart Failure

Heart Failure is a disabling syndrome that affects 6-10% of adults over the age of 65. It is caused by decreased performance of the heart in response to low blood pressure, increase in cardiac muscle and expansion of the left and/or right ventricles. Late stage-heart failure is associated with accumulation of fatty acids within the myocardial tissue resulting from  metabolic changes in the heart. This change is the result  of B oxidation decreases and in response the heart begins to rely on glycolysis for metabolic energy. Interestingly there is opposing evidence for the whether this shift is cardioprotective or damaging. The authors began their research by looking at FASN, the gene encoding fatty acid synthase which produces palmitate, a cardiolipotoxin, and is  the possible link to the fatty acid accumulation during heart failure.

The authors use transgenic mice that express human FASN (tg-FASN) to show that the presence of FASN in myocardial tissue contributes to the occurrence of heart failure like symptoms and to a metabolic shift that is similar to human myocardial tissue during late stage-heart failure. As FASN has crucial functions in different types of tissues, it is a poor target for inhibition to potentially reduce its heart failure effects The authors instead target G-protein-coupled receptor Kinase 2 (GRK-2) for inhibition as it is a known cardioprotective and can regulate pparg through enhancement of ERK cascade activity as shown in figure 1. pparg is a transcription factor that positively regulates FASN and other gene targets, such as UCP1,  that contribute to heart-failure-like symptoms. The authors develop an inhibitor for GSK-2 (GRKInh) to develop tg-GRKInh/FASN mice and find that the GRK-2 inhibitor delays the occurrence of heart failure compared to tg-FASN mice and prevents the metabolic shift to glycolysis that occurs in tg-FASN without the GSK-2 inhibitor by increasing the rate of B oxidation given by relative OCR and ECAR. Using and ERK cascade inhibitor (RKIP), the authors confirm that the GSKInh is down-regulating pparg via the ERK cascade which inactivates pparg by phosphorylation at serine-273. The evidence proposed by this study suggest that the metabolic shift that occurs in late-stage heart failure are actually detrimental to myocardial health and that inhibition of FASN can increase B oxidation and subsequently decrease palmitate thereby preventing lipid overload and cardiomyocyte death. The proposed pathway provides great evidence for the potential of a therapeutic drug that targets GRK-2 in myocardial tissue in the treatment of Heart Failure.

Figure 1: Signaling pathway in which GRK-2 inhibition reduces the lipotoxic effects of FASN and PPARG in myocardial tissue

 

References:

Abd Alla, J., Graemer, M., Fu, X. & Quitterer, U. Inhibition of G-protein-coupled Receptor Kinase 2 Prevents the Dysfunctional Cardiac Substrate Metabolism in Fatty Acid Synthase Transgenic Mice. Journal of Biological Chemistry 291, 2583–2600 (2016).

John JV McMurray, Marc A Pfeffer, Heart failure, The Lancet, Volume 365, Issue 9474, 28 May–3 June 2005, Pages 1877-1889, ISSN 0140-6736, http://dx.doi.org/10.1016/S0140-6736(05)66621-4.
(http://www.sciencedirect.com/science/article/pii/S0140673605666214)

10 Replies to “GRK-2: A Potential Target for Therapeutic Drugs Treating Heart Failure”

  1. Great article Zach. It sounds like Pparg positively regulates a bunch of genes associated with heart failure, including Fasn. Is there any way to determine the expression levels of Pparg and Fasn? If so, we could clinically anticipate heart failure in patients with elevated Fasn or Pparg who have multiple risk factors and catch it early.

    1. Thanks and Abd All et al. used real time quantitative RT-PCR with a LightCycler 480 to determine expression levels of Fasn and Pparg, but I agree that development of expression detection for Pparg could be important for determining risk of heart failure.

  2. Great summary of the article. Very informative.

    The authors point out that while the inhibition of GRK2 promotes lessened cardiotoxic phenotypes the inhibition of GRK2 and ERK pathways did not. This is attributed to the ERK inhibition causing an up-regulation in pparg. However, since GRK2 inhibition acts in part to down-regulate ERK how does this produce a differing effect? Could there be a different unexplored pathway linking GRK2, ERK and cardiotoxic factors? How might levels of ADIPOQ, UPC1 and RETN be different when ERK is inhibited, GRK2 is inhibited and both are inhibited?

    1. Thank you
      From my understanding inhibition of GRK2 actually enhances the activity of the ERK cascade which leads to increase in pparg phosphorylation (inactivation). That is why GRK2 inhibition and ERK inhibition by RKIP did not lessen the cardiotoxic phenotype; inhibition of ERK prevented phosphorylation of pparg (remained active) and the tg-FASN mice had the cardiotoxic phenotype. I’m sure there could be an unexplored part of this pathway that likely contributes to ERK regulation (as it ERK cascade has multiple functions in different tissue through the body. levels of Pparg targets, ADIPOQ, UCP1 and RETN, are lower when pparg is inactivated by phosphorylation. GRK2 inhibition increases pparg inactivation by enhancing activity of the ERK cascade. ERK inhibition would increases pparg activation and levels of pparg targets would increase. Inhibition of both ERK and GRK2 would have the same phenotype as ERK inhibition.

  3. Very good summary of the article that gives a lot of information to the reader in a very succinct manner. You mentioned that FASN would not be a target for inhibition because it has critical functions for various other tissues; however Figure 1 shows its inhibition in the signaling pathway. Is this inhibition the result of PPARG inhibition or GRK2 inhibition or both? Additionally, I am curious about any negative side effects that result from GRK2 inhibition in relation to its effect on FASN. Do you know of any other studies that speak to these types of side effects?

    1. Thank you. The inhibition of FASN is the result of GRK2 inhibition which causes an increase in pparg inactivation. So FASN expression is lowered directly by pparg inactivation, but GRK2 is the protein that was initially inhibited and caused the subsequent pparg inactivation. My reply to Elaine discusses this particular pathway in a bit more detail. I am not aware of any side effects of GRK2 in relation to its effect on FASN, this article was posted Feb 5 and is predominantly about establishing that the link between GRK2, FASN, pParg, and lipotoxicity and it was performed in mice so there is not a lot of research that considers the side effects of GRK2 inhibition on FASN.

      Ramos, Joe W. 2008. “The Regulation of Extracellular Signal-Regulated Kinase (ERK) in Mammalian Cells.” The International Journal of Biochemistry & Cell Biology 40 (12): 2707–19. doi:10.1016/j.biocel.2008.04.009.

  4. Great job Zach. Your summary was really helpful to me in understanding this paper. However, there is a point of confusion for me. The authors decide not to target FASN due to its function in tissue types other than myocardial. Instead, they focus on inhibiting GRK-2, but isn’t inhibiting GRK-2 just another indirect way of inhibiting FASN, according to the pathway? How would this affect the other tissues, which FASN acts on, any differently? Also, was there any indication that these results could be duplicated in humans?

    1. Thanks. GRK2 was chosen because there was existing literature indicating the cardioprotective phenotype of GRK2 inhibition and since they chose not to target FASN for its role as an essential enzyme that has indispensable functions in energy homeostasis, membrane biology, and neurogenesis, I would assume inhibition of GRK2 could be isolated in cardiomyocytes or simply GRK2 is not as esstential as FASN. “Although the study was performed with experimental mouse models, the data could also be relevant for the human disease because FASN up-regulation is a characteristic feature of
      patients with heart failure” (Abd Alla 2016)

  5. I really enjoyed this summary of the article as it made the problem, the experiment, and the results really clear without being too long. You stated that GRK2 inhibition delayed the occurrence of heart failure. Does this mean that heart failure will still occur, or is it completely prevented? If it still occurs, is it possibly due to the fact that FASN is being inhibited, even though it’s an indirect inhibition through GRK2?

    1. Thanks, The GRK2 inhibition delayed the onset of heart failure caused by FASN, so onset of heart failure still occurred but later when compared to the tg-FASN mice. Heart failure still occurs because the experiments are performed predominantly with tg-FASN mice which have a heart failure-like phenotype caused by elevated FASN expression. The GRK2 inhibition helps to reduce FASN expression, but it is not lowered enough to prevent heart failure onset.

Comments are closed.