Desmin deficiency affects the microenvironment of the cardiac side population and Sca1+ stem cell population of the adult heart and impairs their cardiomyogenic commitment.

The heart's limited regenerative capacity raises the need for novel stem cell-based therapeutic approaches for cardiac regeneration. However, the use of stem cells is restrictive due to poor determination of their properties and the factors that regulate them. Here, we investigated the role of desmin, the major muscle-specific intermediate filament protein, in the characteristics and differentiation capacity of cardiac side population (CSP) and Sca1+ stem cells of adult mice. We found that desmin deficiency affects the microenvironment of the cells and leads to increased numbers of CSP but not Sca1+ cells; CSP subpopulation composition is altered, the expression of the senescence marker p16INK4a in Sca1+ cells is increased, and early cardiomyogenic commitment is impaired. Specifically, we found that mRNA levels of the cardiac transcription factors Mef2c and Nkx2.5 were significantly reduced in des-/- CSP and Sca1+ cells, while differentiation of CSP and Sca1+ cells demonstrated that in the absence of desmin, the levels of Nkx2.5, Mef2c, Tnnt2, Hey2, and Myh6 mRNA are differentially affected. Thus, desmin deficiency restricts the regenerative potential of CSP and Sca1+ cells, both directly and indirectly through their microenvironment.

Three in a Box: Understanding Cardiomyocyte, Fibroblast, and Innate Immune Cell Interactions to Orchestrate Cardiac Repair Processes.

Following an insult by both intrinsic and extrinsic pathways, complex cellular, and molecular interactions determine a successful recovery or inadequate repair of damaged tissue. The efficiency of this process is particularly important in the heart, an organ characterized by very limited regenerative and repair capacity in higher adult vertebrates. Cardiac insult is characteristically associated with fibrosis and heart failure, as a result of cardiomyocyte death, myocardial degeneration, and adverse remodeling. Recent evidence implies that resident non-cardiomyocytes, fibroblasts but also macrophages -pillars of the innate immunity- form part of the inflammatory response and decisively affect the repair process following a cardiac insult. Multiple studies in model organisms (mouse, zebrafish) of various developmental stages (adult and neonatal) combined with genetically engineered cell plasticity and differentiation intervention protocols -mainly targeting cardiac fibroblasts or progenitor cells-reveal particular roles of resident and recruited innate immune cells and their secretome in the coordination of cardiac repair. The interplay of innate immune cells with cardiac fibroblasts and cardiomyocytes is emerging as a crucial platform to help our understanding and, importantly, to allow the development of effective interventions sufficient to minimize cardiac damage and dysfunction after injury.

Desmin enters the nucleus of cardiac stem cells and modulates Nkx2.5 expression by participating in transcription factor complexes that interact with the nkx2.5 gene.

The transcription factor Nkx2.5 and the intermediate filament protein desmin are simultaneously expressed in cardiac progenitor cells during commitment of primitive mesoderm to the cardiomyogenic lineage. Up-regulation of Nkx2.5 expression by desmin suggests that desmin may contribute to cardiogenic commitment and myocardial differentiation by directly influencing the transcription of the nkx2.5 gene in cardiac progenitor cells. Here, we demonstrate that desmin activates transcription of nkx2.5 reporter genes, rescues nkx2.5 haploinsufficiency in cardiac progenitor cells, and is responsible for the proper expression of Nkx2.5 in adult cardiac side population stem cells. These effects are consistent with the temporary presence of desmin in the nuclei of differentiating cardiac progenitor cells and its physical interaction with transcription factor complexes bound to the enhancer and promoter elements of the nkx2.5 gene. These findings introduce desmin as a newly discovered and unexpected player in the regulatory network guiding cardiomyogenesis in cardiac stem cells.

Strategies to Study Desmin in Cardiac Muscle and Culture Systems.

Intermediate filament (IF) cytoskeleton comprises the fine-tuning cellular machinery regulating critical homeostatic mechanisms. In skeletal and cardiac muscle, deficiency or disturbance of the IF network leads to severe pathology, particularly in the latter. The three-dimensional scaffold of the muscle-specific IF protein desmin interconnects key features of the cardiac muscle cells, including the Z-disks, intercalated disks, plasma membrane, nucleus, mitochondria, lysosomes, and potentially sarcoplasmic reticulum. This is crucial for the highly organized striated muscle, in which effective energy production and transmission as well as mechanochemical signaling are tightly coordinated among the organelles and the contractile apparatus. The role of desmin and desmin-associated proteins in the biogenesis, trafficking, and organelle function, as well as the development, differentiation, and survival of the cardiac muscle begins to be enlightened, but the precise mechanisms remain elusive. We propose a set of experimental tools that can be used, in vivo and in vitro, to unravel crucial new pathways by which the IF cytoskeleton facilitates proper organelle function, homeostasis, and cytoprotection and further understand how its disturbance and deficiency lead to disease.

Polymorphisms of caspase 8 and caspase 9 gene and colorectal cancer susceptibility and prognosis.

PURPOSE: Caspase-8 (CASP8) and caspase-9 (CASP9) play crucial roles in regulating apoptosis, and their functional polymorphisms may alter cancer risk. Our aim was to investigate the association between CASP8 and CASP9 gene polymorphisms and colorectal cancer (CRC) susceptibility. METHODS: A case-control study at 402 CRC patients and 480 healthy controls was undertaken in order to investigate the association between the genotype and allelic frequencies of CASP8 -652 6N ins/del and CASP9 -1263 A>G polymorphisms and the CRC susceptibility. The polymerase chain reaction (PCR) restriction fragment length polymorphism method was used and the incidence of polymorphisms on messenger RNA (mRNA) expression levels was detected by quantitative reverse-transcriptase PCR in CRC tissues. RESULTS: No statistical significant association was observed between CASP8 -652 6N ins/del polymorphism frequencies and CRC susceptibility. CASP9 -1263 G allele was observed to be significant associated with reduced risk of CRC. Homozygotes for the -1263 GG CASP9 genotype, and hetrozygotes for the -1263 AG genotype expressed 6.64- and 3.69-fold higher mRNA levels of Caspase-9, respectively compared to the -1263 AA genotype cases. No significant association was observed between CASP9 -1263 A>G polymorphism and tumor characteristics. The CASP9 -1263 GG genotype was associated with increased overall survival in CRC patients. CONCLUSION: The CASP9 -1263 A>G polymorphism was observed to play a protective role in CRC predisposition, while the CASP9 -1263 GG genotype may confer a better prognosis at CRC patients.