MyoD-induced reprogramming of human fibroblasts and urinary stem cells in vitro: protocols and their applications

Efficacy of Cystic Fibrosis Transmembrane Regulator Corrector C17 in Beta-Sarcoglycanopathy-Assessment of Patient's Primary Myotubes

Limb-girdle muscular dystrophy type 2E/R4 (LGMD2E/R4) is a rare disease that currently has no cure. It is caused by defects in the SGCB gene, mainly missense mutations, which cause the impairment of the sarcoglycan complex, membrane fragility, and progressive muscle degeneration. Here, we studied the fate of some β-sarcoglycan (β-SG) missense mutants, confirming that, like α-SG missense mutants, they are targeted for degradation through the ubiquitin-proteasome system. These data, collected using HEK-293 cells expressing either the I119F- or Y184C mutants of β-SG, were subsequently confirmed in primary myotubes derived from an LGMD2E/R4 patient carrying a homozygous I92T mutation. The knowledge that β-SG with an amino acid substitution shares a pathway of degradation with α-SG mutants, allowed us to explore the pharmacological approach successfully tested in LGMD2D/R3. Several CFTR correctors, particularly corrector C17, preserved β-SG mutants from degradation and promoted localization at the sarcolemma of the entire SG complex. The presence of the complex, despite containing a mutated subunit, improved sarcolemma integrity, as evidenced by the reduced creatine kinase release from myotubes under hypoosmotic stress. These results suggest that β-SG missense mutants undergo proteasomal degradation as α-SG mutants, and that CFTR correctors, particularly C17, may be used as a potential therapeutic option for recovering and stabilizing the SG complex in patients with sarcoglycanopathies.

Golodirsen restores DMD transcript imbalance in Duchenne Muscular Dystrophy patient muscle cells

BACKGROUND

Antisense oligonucleotides (AON) represent a promising treatment for Duchenne muscular dystrophy (DMD) carrying out-of-frame deletions, but also show limitations. In a completed clinical trial golodirsen, approved by FDA to induce skipping of DMD gene exon 53 in eligible patients, we demonstrated increase in DMD expression and protein production, albeit with inter-patient variability.

METHODS

Here, we investigate further the golodirsen mechanism of action using myotubes derived from MyoD transfected fibroblasts isolated from DMD patients at the baseline of the clinical trial SRP-4053.

RESULTS

We confirm golodirsen's selectivity and efficiency in removing only exon 53. For the first time in human cells, we revealed a significant reduction in the so called DMD "transcript imbalance", in golodirsen-treated DMD muscle cultures. The transcript imbalance is a unique DMD phenomenon characterized by non-homogeneous transcript expression along its entire length and responsible for the reduced stability of the transcript. Our in-vivo study also showed that the efficiency of exon skipping did not always correspond to a proportional restoration of the dystrophin protein. Predominant nuclear localization of the DMD transcript, observed in patients and animal models, persists even after exon skipping.

CONCLUSION

All these findings suggest challenges other than AON delivery for high level of protein restoration in DMD, highlighting the importance of investigating the biological mechanisms upstream of protein production to further enhance the efficiency of any AON treatment in this condition.

Stable and Oscillatory Hypoxia Differentially Regulate Invasibility of Breast Cancer Associated Fibroblasts

As local regions in the tumor outstrip their oxygen supply, hypoxia can develop, affecting not only the cancer cells, but also other cells in the microenvironment, including cancer associated fibroblasts (CAFs). Hypoxia is also not necessarily stable over time, and can fluctuate or oscillate. Hypoxia Inducible Factor-1 is the master regulator of cellular response to hypoxia, and can also exhibit oscillations in its activity. To understand how stable, and fluctuating hypoxia influence breast CAFs, we measured changes in gene expression in CAFs in normoxia, hypoxia, and oscillatory hypoxia, as well as measured change in their capacity to resist, or assist breast cancer invasion. We show that hypoxia has a profound effect on breast CAFs causing activation of key pathways associated with fibroblast activation, but reduce myofibroblast activation and traction force generation. We also found that oscillatory hypoxia, while expectedly resulted in a "sub-hypoxic" response in gene expression, it resulted in specific activation of pathways associated with actin polymerization and actomyosin maturation. Using traction force microscopy, and a nanopatterned stromal invasion assay, we show that oscillatory hypoxia increases contractile force generation vs stable hypoxia, and increases heterogeneity in force generation response, while also additively enhancing invasibility of CAFs to MDA-MB-231 invasion. Our data show that stable and unstable hypoxia can regulate many mechnobiological characteristics of CAFs, and can contribute to transformation of CAFs to assist cancer dissemination and onset of metastasis.