Blastocyst injection of embryonic stem cells: a simple approach to unveil mechanisms of corrections in mouse models of human disease

Muscle and cardiac therapeutic strategies for Duchenne muscular dystrophy: past, present, and future

BACKGROUND

Duchenne muscular dystrophy (DMD) is a severe X-linked neuromuscular childhood disorder that causes progressive muscle weakness and degeneration and results in functional decline, loss of ambulation and early death of young men due to cardiac or respiratory failure. Although the major cause of the disease has been known for many years-namely mutation in the DMD gene encoding dystrophin, one of the largest human genes-DMD is still incurable, and its treatment is challenging.

METHODS

A comprehensive and systematic review of literature on the gene, cell, and pharmacological experimental therapies aimed at restoring functional dystrophin or to counteract the associated processes contributing to disease progression like inflammation, fibrosis, calcium signaling or angiogenesis was carried out.

RESULTS

Although some therapies lead to satisfying effects in skeletal muscle, they are highly ineffective in the heart; therefore, targeting defective cardiac and respiratory systems is vital in DMD patients. Unfortunately, most of the pharmacological compounds treat only the symptoms of the disease. Some drugs addressing the underlying cause, like eteplirsen, golodirsen, and ataluren, have recently been conditionally approved; however, they can correct only specific mutations in the DMD gene and are therefore suitable for small sub-populations of affected individuals.

CONCLUSION

In this review, we summarize the possible therapeutic options and describe the current status of various, still imperfect, strategies used for attenuating the disease progression.

Comprehensive models of human primary and metastatic colorectal tumors in immunodeficient and immunocompetent mice by chemokine targeting

Current orthotopic xenograft models of human colorectal cancer (CRC) require surgery and do not robustly form metastases in the liver, the most common site clinically. CCR9 traffics lymphocytes to intestine and colorectum. We engineered use of the chemokine receptor CCR9 in CRC cell lines and patient-derived cells to create primary gastrointestinal (GI) tumors in immunodeficient mice by tail-vein injection rather than surgery. The tumors metastasize inducibly and robustly to the liver. Metastases have higher DKK4 and NOTCH signaling levels and are more chemoresistant than paired subcutaneous xenografts. Using this approach, we generated 17 chemokine-targeted mouse models (CTMMs) that recapitulate the majority of common human somatic CRC mutations. We also show that primary tumors can be modeled in immunocompetent mice by microinjecting CCR9-expressing cancer cell lines into early-stage mouse blastocysts, which induces central immune tolerance. We expect that CTMMs will facilitate investigation of the biology of CRC metastasis and drug screening.

Injection of wild type embryonic stem cells into Mst1 transgenic blastocysts prevents adult-onset cardiomyopathy

Embryonic stem cells have the capacity to differentiate into a wide range of cell types. We previously described that blastocyst injection of wild type (WT) embryonic stem cells (ESCs) into various knockout (KO) mouse models of human disease prevents disease from occurring. In this study we ask if the blastocyst approach can also correct defects in a mouse model of transgenic (Tg) overexpression of a pro-apoptotic factor. We injected ROSA26 (LacZ-marked) WT ESCs into human mammalian sterile 20 like-kinase 1 (Mst1) Tg blastocysts. Mst1 Tg mice overexpress Mst1, a pro-apoptotic factor, in a cardiac-specific manner. As a result, Mst1 Tg mice develop adult dilated cardiomyopathy driven by apoptosis, reduction in cell density and no hypertrophic compensation. Incorporation of WT ESCs generated WT/Mst1 chimeric mice with normal hearts at histological and functional levels. Accordingly, apoptosis and cell density parameters were normalized. The experiments suggest that an adult-onset cardiac myopathy induced by overexpression of the pro-apoptotic Mst1 can be reversed by developmental incorporation of WT ESCs. The findings also suggest that since forced expression of the Mst1 transgene is not abolished in the rescued chimeras, the WT ES-derived cells normalize pathways that lie downstream of Mst1. The results expand the therapeutic capability of the ESCs to mouse models that overproduce detrimental proteins.

Developmental ablation of Id1 and Id3 genes in the vasculature leads to postnatal cardiac phenotypes

The Id1 and Id3 genes play major roles during cardiac development, despite their expression being confined to non-myocardial layers (endocardium-endothelium-epicardium). We previously described that Id1Id3 double knockout (dKO) mouse embryos die at mid-gestation from multiple cardiac defects, but early lethality precluded the studies of the roles of Id in the postnatal heart. To elucidate postnatal roles of Id genes, we ablated the Id3 gene and conditionally ablated the Id1 gene in the endothelium to generate conditional KO (cKO) embryos. We observed cardiac phenotypes at birth and at 6 months of age. Half of the Id cKO mice died at birth. Postnatal demise was associated with cardiac enlargement and defects in the ventricular septum, trabeculation and vasculature. Surviving Id cKO mice exhibited fibrotic vasculature, cardiac enlargement and decreased cardiac function. An abnormal vascular response was also observed in the healing of excisional skin wounds of Id cKO mice. Expression patterns of vascular, fibrotic and hypertrophic markers were altered in the Id cKO hearts, but addition of Insulin-Like Growth Factor binding protein-3 (IGFbp3) reversed gene expression profiles of vascular and fibrotic, but not hypertrophic markers. Thus, ablation of Id genes in the vasculature leads to distinct postnatal cardiac phenotypes. These findings provide important insights into the role/s of the endocardial network of the endothelial lineage in the development of cardiac disease, and highlight IGFbp3 as a potential link between Id and its vascular effectors.