Cardiomyocytes for myocardial regeneration

The pumping mechanism of the heart is adjusted by the network of coronary arteries and cardiac veins . Myocardial infarction ocurs when the blood supply is disrupted . In the progressive form , this may lead to heart failure .

The repopulation of the scar is achieved through various methods . One of them is to use autologous bone marrow cells . Another strategy is to differentiate the cardiac progenitor cells ( CPC ) . A third direction is to use cardiomyocytes ( CMs ) derived from human embryonic stem cells ( hESC ) , hESCs cardiac progenitor cells ( hESC - CPC ) , human pluripotent stem cells ( hPSCs ) , or human induced pluripotent stem cells ( hiPSCs ) for the transplantation in the myocardium .

The review paper Concise review : reprogramming strategies for cardiovascular regenerative medicine : from induced pluripotent stem cells to direct reprogramming analyses more than a hundred papers . Three reprogramming strategies for the myocardial regeneration are brought in discussion ( figure 1 ) : the iPSCs technology , the partially reprogramming method and the direct set of approaches .

Figure 1 . The CMs derived from the iPSC ( top ) , the partial reprogramming ( middle ) , and the direct reprogramming technology ( below ) .

The hESCs represent the first reliable source for cardiomyocytes in vitro . The immune rejection , and the patient – or disease – specific hESCs are two challenges for the clinical allogeneic cell transplantation .

The hESCs and hiPSCs may generate beating cardiomyocytes in an inefficient method . The canonical Wnt pathway uses hiPSCs and small molecules in a more efficient signaling strategy .

Cardiomyocytes are partially reprogrammed from the iPSCs through a technology developed in 2006 . It takes a few months to differentiate the colonies of hiPSCs into the cardiac lineage . The use of partially reprogrammed cells reduces the length of time for the process to 11 – 12 days . There are also challenges for reaching the clinical practice ( figure 2 ) . Some of them are : the phenotypic heterogeneity of the differentiating CMs , the tumorigenic risk , and the poor in – vivo survival .

Figure 2 . The phases and challenges of the partially reprogrammed iPSCs method towards clinical practice .

The process of direct reprogramming of fibroblasts into induced cardiomyocyte cells ( iCMs ) is epigenetically stable . It is achieved through various combinations : by adding the Hand2 to the Gata4 , Mef2c and Tbx5 combination of transcription factors ; by using myocardin , and a combination of the Mef2c and Tbx5 transcription factors ; through a combination of a Janus inhibitor and four microRNAs ; by mixing two microRNAs and four transcription factors . The challenges of the myocardial regeneration are reduced through the deliver of reprogramming factors directly to the cardiac tissue .

Progress in the regeneration therapy is achieved if further studies are performed on early stages of myocardial infarction , if the stem cells delivered in – vivo generate efficiently new myocardium , and if the newly developed myocardium has suitable performance for the patient .

Hybrid bioprosthetic heart valve

The peer - reviewed publication Engineering of a bio – functionalized hybrid off – the – shelf heart valve caught my interest . The growth factor signalling mechanism inside the bioprosthetic heart valve is different from the native valve . The Young ' s modulus quantifies the remodeling behaviour after implantation .

The chosen method to generate the scaffold is the electrospinning of either poly - lactide acid ( PLA ) or equal amounts of it and poly - ethylene glycol dimethacrylate ( PEGdma ) . The performance of the polymeric scaffold is tested under physiological conditions . The blood is assumed to interact with the heart valve leaflet at large amplitude , in a laminar flow , under oscillatory shear stress . The nonlinear flow properties affect the response of the heart valve .

Valvular endothelial and interstitial cells are seeded in the scaffold . The protein configuration is visualised on the cell – seeded polymeric scaffolds using immunofluorescence staining . The cell viability is assessed with 3 - ( 4 , 5 - dimethyl – 2 - thiazolyl ) - 2 , 5 - diphenyl - 2 H - tetrazolium bromide ( MTT assay ) . The cells are compatible with both the PLA and the PEGdma – PLA scaffold . The valvular endothelial cells adhere in a greater amount onto the PEGdma – PLA scaffold than on the one with PLA fibres . The valvular interstitial cells adhere similarly on both polymeric scaffolds . The valvular actin cytoskeleton for both the endothelian and the interstitial cells is more visible in the PEGdma – PLA than in the plain PLA scaffold .

Native porcine aortic valve tissue , unseeded and cell – seeded polymeric scaffolds are analysed using the scanning electron microscopy ( SEM ) . The PLA scaffold has 30 times greater fibre diameter and 1160 times greater pore size than the native leaflet .

The atomic composition of the surfaces is determined using the electron spectroscopy for chemical analysis ( ESCA ) . The comparison of the data is made using literature values for single components . The PLA – PEGdma scaffold has both PLA and PEGdma groups on the analysed surface .

The mechanical properties of both native and polymeric scaffolds are using the atomic force microscopy ( AFM ) . The spongiosa is the softest layer of the native porcine leaflet , with a Young ' s modulus twice as small as the one for the ventricularis and fibrosa layer . The Young ' s modulus of the PLA – PEGdma scaffold is 10 times greater than the ventricularis and fibrosa native layer .

Uniaxial tensile testing provides information regarding the Young ' s modulus , the tensile strength and the elongation values . Both the PLA scaffold and the native leaflet is soft , with similar values for the Young ' s modulus . The computed Young ' s modulus for the PLA – PEGdma scaffold is twice the value for the PLA scaffold . The PLA scaffold is 55 times more expansible than the native leaflet . The tensile strength value is similar for both the PLA and PLA – PEGdma scaffold .

The polarity of the molecules on the surface is detected using the contact angle goniometry technique . The PLA scaffold is highly hydrophobic . The PEGdma scaffold is hydrophilic . The PLA – PEGdma scaffold is highly hydrophilic . The PLA – PEGdma is highly hydrophilic .

The capacity of water - holding of both the native and the polymeric scaffolds is compared . The PLA scaffold has 11 % water intake capacity , the PEGdma scaffold has high value , while the native leaflet has 90 % . The PLA – PEGdma scaffold has 5 times more water intake capacity than the PLA scaffold .

The protein expression patterns are revealed in the early development for the human heart tissue . Collagen type 1 is present in the leaflets , Versican in the atria – ventricular valves and in the outflow tract , in the first trimester of the fetal development . Collagen type 1 is present in the fibrosa layer of the aortic valve , Versican in the leaflet tip and close to the arterial wall , in the second semester of the fetal development . The valvular histoarchitecture in the 19 years old adolescent is similar to the one in the second semester of the fetal development .

The bio – functionalised prosthetic leaflet has PLA – PEGdma scaffold , Collagen type 1 gel layer , and Versican tip , in a proof – of – principle experiment . The polymeric scaffold requires further structural modifications to have a biocompatible material with a set of mechanical properties closer to the one of the human heart valve .

References :

Hinderer S . , Seifert J . , Votteler M . , Shen N . , Rheinlaender J . , Schaffer T . E . , Schenke – Layland K . ( 2014 ) “ Engineering of a bio – functionalized hybrid off – the – shelf heart valve ” , Biomaterials , 35 ( 7 ) , 2130 – 2139 .

Hyun K . , Wilhelm M . , Klein C . O . , Cho K . S . , Nam J . G . , Ahn H. , Lee S . J . , Ewoldt R . H . , McKinley G . H . ( 2011 ) “ Progress in Polymer Science ” , 36 ( 12 ) , 1697 – 1753 .