Conference notes on the first day of the The New Cardiobiology 2024 organized in Heidelberg 19-22.2. Despite being the first edition of the meeting was super organized and packed with good talks.

Keynote 1: Christine Mummery

The efficiency of current pharmacological treatments is not very high. In fact, for 10 top selling drugs in US, for one patient which benefited from the treatment there are 3 to 24 patients who do not improve.

Therefore we need to do more research on as mature cardiomyocytes as possible, the current differentiation methods get you to a week 16 of gestation. One of the challenges is the cost of the differentiation. Their protocol enables differentiation of all three cell types found in the heart from ipscs (Campostrini et al. 2021, Nat. Protoc.)

Maturation requires different cell types

T-tubule structure is one of the hallmarks of maturation and is absent in hIPSC-CMs. In similar vein the action potential of mature cardiomyocyte has the notch after the first rise. This is also missing in hiPSCs derived cardiomyocytes.Better maturation can be achieved by co-culture with cardiac fibroblasts, where the connections of fibroblasts with cardiomyocytes mediated by Cx43 are essential. It is not fibroblasts only though, the NO produced by endothelial cells is essential to regulate both cardiomyocytes and fibroblasts.

Coculutures of different genetic backgrounds

Coculture of cardiomyocytes, fibroblasts, and endothelial cells with a different genetic mutations and backgrounds looks like an increasingly popular approach in the community enabled by the microtissues approach. In her presentation the effects of SCN5A mutant variants through MBLN1 were presented.

Microtissues for the pharma

Microtissues are the way to go for pharma testing. The main reasons are better fit of cardimyocytes response to the known drugs when compared with 2D and lower cost then otherwise used rabbit cardiomyocytes. Fun fact: datapoint cost of pharma per datapoint is $0,25, and microtissues are cheaper;).

3D required for modelling of vascular disease

Example of a HHT syndrome of profound nose bleeding, which could be investigated only in 3d using the vascular chip from AIM, available commerically.

Q/A

  • the fibroblasts in microtissues do not overgrow cardiomyocytes in 3-4 weeks
  • The electrophysiological measurments of microtissue embedded cardiomyocytes are done on resuspended cardiomyocytes.
  • they do the interaction with macrophages in tissue constructs already, requires some technical trick for them not to migrate out.

Papers

Alessandro Bertero

New system to screen shRNA in iPSC-CMs iPS2-seq

Alessandro has a history in making promoters which do not get silenced in iPSCs and CMs, they published it in Development (Bertero..Valler, 2016) and Curr. Prot. Stem. Cells (Bertero, 2018).

Now they moved it up a notch to enable higher throughput screening of shRNAs by emplyoing doouble barcoding system (one for the shRNA, one for the clone of ips which was transfected).

Applications1 - Single ventricle disease

To show how this works they selected a nicely defined model of left ventricle hypoplasia. The only alternative is a surgery or implantation of new cardiomyocytes to regrow the wall (Li..Murry, Nat. Biotech, 2018).

However the regrowth brings challenge in the integration and final maturation of those new cardiomyocytes. Therefore they used shRNA to supress expression of HCN4, NCX1, Cav1.2, and OE of KCNJ2 to get a mature phenotype. Therapy with these cells called “MEDUSA” results in success (Marchiano,2023, Cell Stem Cell).

Applications2 - Mass production

Propagation and differentiation of stem cells into sufficient amount of cells is very costly. This is a problem not only of regenerative medicine, but also lab-grown meat which will be a part of agriculture in future. He suggests that methods which use stem cell reprogramming will be used in both and will democratize therapy in the future.

Papers

Catherine Wilson

Myc is the king but needs some helpers

Myc regulates one third of all human genes and is essential for proliferation. However overexpressing myc in cardiomyocytes does not lead into proliferating cardiomyocytes. The limiting factor is a complex of CDK9 and CycT1. And in cardiomyocytes the limiting factor is CycT1 and she shows that using tamoxifen inducible CycT1 proliferation of cardiomyocytes can be restarted.

Too much myc will kill you

HOwever the pan-heart induction of CycT1 kills the mice, so it needs to be targeted by(by injection) into the scar region and there it works. The further refinement of the method is using modRNAs which can be used therapeutically.

Papers

Juan Antonio Guadix - sacrifical mold for mini heart creation

Interesting model, where by sacrificil molding whole “heart” can be layer by layer assembled.
The unique thing is it is very nicely defined by shape and has a one hole which can be used for pressurizing the construct.
Have collaboration with university in sunny Malaga:).

Gergana Dobrava - Genetic and epigenetic regulation of cardiovascular development and disease

Gregana looks into developmental disease, Tetralogy of fallot, whose patients have very low oxygen saturation (<88%).
SHe found that in her cohort the RNF20 is the culprit. Doing work in mouse she observes that RNF20-/- animals have more mature cardiomyocytes, but less endothelial cells.\

This together with defects in the structures originating from second heart fiels (SHF) results in smaller ventricles and thin myocardium. When looking into a molecular mechanism, she can see that RNF20 deficiency leads to upregulation of TGF-beta signalling, ECM production and decrease in contractility. To verify the mechanism she knocked-out TGF-beta and collagen, which rescues the phenotype.

Some more information about RNF20:

  • it is downregulated in cancer
  • exposure to arsenic (tobacco smoke) inhibits RNF20
  • RNF20 is also a mechanosensor

Papers

Tzahor&Dimmeter, 2022: review not sure whether useful.

Omar Mourad

ENthusiastic and thoughtful PhD student from Vasconcelos lab was showing a nice alternative to the engineered heart tissue.

Different setup for EHT

In his setup, the thin pillars are layed horizontally above a recentagle well milled in plastic. Measures deflection of the pillars when contracted, also passive tension, and can also do some calcium imaging.