Background— Systemic delivery of bone marrow–derived mesenchymal stem cells (BM-MSCs) is an attractive approach for myocardial repair. We aimed to test this strategy in a rat model after myocardial infarction (MI). Methods and Results— BM-MSCs were obtained from rat bone marrow, expanded in vitro to a purity of >50%, and labeled with ^99m Tc exametazime, fluorescent dye, LacZ marker gene, or bromodeoxyuridine. Rats were subjected to MI by transient coronary artery occlusion or to sham MI. ^99m Tc-labeled cells (4×10 ⁶ ) were transfused into the left ventricular cavity of MI rats either at 2 or 10 to 14 days after MI and were compared with sham-MI rats or MI rats treated with intravenous infusion. Gamma camera imaging and isolated organ counting 4 hours after intravenous infusion revealed uptake of the ^99m Tc-labeled cells mainly in the lungs, with significantly smaller amounts in the liver, heart, and spleen. Delivery by left ventricular cavity infusion resulted in drastically lower lung uptake, better uptake in the heart, and specifically higher uptake in infarcted compared with sham-MI hearts. Histological examination at 1 week after infusion identified labeled cells either in the infarcted or border zone but not in remote viable myocardium or sham-MI hearts. Labeled cells were also identified in the lung, liver, spleen, and bone marrow. Conclusions— Systemic intravenous delivery of BM-MSCs to rats after MI, although feasible, is limited by entrapment of the donor cells in the lungs. Direct left ventricular cavity infusion enhances migration and colonization of the cells preferentially to the ischemic myocardium.

Background—The myocardium is unable to regenerate because cardiomyocytes cannot replicate after injury. The heart is therefore an attractive target for tissue engineering to replace infarcted myocardium and enhance cardiac function. We tested the feasibility of bioengineering cardiac tissue within novel 3-dimensional (3D) scaffolds. Methods and Results—We isolated and grew fetal cardiac cells within 3D porous alginate scaffolds. The cell constructs were cultured for 4 days to evaluate viability and morphology before implantation. Light microscopy revealed that within 2 to 3 days in culture, the dissociated cardiac cells form distinctive, multicellular contracting aggregates within the scaffold pores. Seven days after myocardial infarction, rats were randomized to biograft implantation (n=6) or sham-operation (n=6) into the myocardial scar. Echocardiography study was performed before and 65±5 days after implantation to assess left ventricular (LV) remodeling and function. Hearts were harvested 9 weeks after implantation. Visual examination of the biograft revealed intensive neovascularization from the neighboring coronary network. Histological examination revealed the presence of myofibers embedded in collagen fibers and a large number of blood vessels. The specimens showed almost complete disappearance of the scaffold and good integration into the host. Although control animals developed significant LV dilatation accompanied by progressive deterioration in LV contractility, in the biograft-treated rats, attenuation of LV dilatation and no change in LV contractility were observed. Conclusions—Alginate scaffolds provide a conducive environment to facilitate the 3D culturing of cardiac cells. After implantation into the infarcted myocardium, the biografts stimulated intense neovascularization and attenuated LV dilatation and failure in experimental rats compared with controls. This strategy can be used for regeneration and healing of the infarcted myocardium.

Gene mutations, mostly segregating with a dominant mode of inheritance, are important causes of dilated cardiomyopathy (DCM), a disease characterized by enlarged ventricular dimensions, impaired cardiac function, heart failure and high risk of death. Another myocardial abnormality often linked to gene mutations is left ventricular noncompaction (LVNC) characterized by a typical diffuse spongy appearance of the left ventricle. Here, we describe a large Bedouin family presenting with a severe recessive DCM and LVNC. Homozygosity mapping and exome sequencing identified a single gene variant that segregated as expected and was neither reported in databases nor in Bedouin population controls. The PLEKHM2 cDNA2156_2157delAG variant causes the frameshift p.Lys645AlafsTer12 and/or the skipping of exon 11 that results in deletion of 30 highly conserved amino acids. PLEKHM2 is known to interact with several Rabs and with kinesin-1, affecting endosomal trafficking. Accordingly, patients' primary fibroblasts exhibited abnormal subcellular distribution of endosomes marked by Rab5, Rab7 and Rab9, as well as the Golgi apparatus. In addition, lysosomes appeared to be concentrated in the perinuclear region, and autophagy flux was impaired. Transfection of wild-type PLEKHM2 cDNA into patient's fibroblasts corrected the subcellular distribution of the lysosomes, supporting the causal effect of PLEKHM2 mutation. PLEKHM2 joins LAMP-2 and BAG3 as a disease gene altering autophagy resulting in an isolated cardiac phenotype. The association of PLEKHM2 mutation with DCM and LVNC supports the importance of autophagy for normal cardiac function.