Satellite cells reside in defined niches and are activated upon skeletal muscle injury to facilitate regeneration. Mechanistic studies of skeletal muscle regeneration are hampered by the inability to faithfully simulate satellite cell biology in vitro. We sought to overcome this limitation by developing tissue engineered skeletal muscle (ESM) with (1) satellite cell niches and (2) the capacity to regenerate after injury. ESMs contained quiescent Pax7‐positive satellite cells in morphologically defined niches. Satellite cells could be activated to repair (i) cardiotoxin and (ii) mechanical crush injuries. Activation of the Wnt‐pathway was essential for muscle regeneration. Finally, muscle progenitors from the engineered niche developed de novo ESM in vitro and regenerated skeletal muscle after cardiotoxin‐induced injury in vivo. We conclude that ESM with functional progenitor niches reminiscent of the in vivo satellite cell niches can be engineered in vitro. ESM may ultimately be exploited in disease modeling, drug screening, or muscle regeneration.

IR leads to a major arrest in the G(1)/S phase and to a lesser extent in the G(2)/M transition of the cell cycle, resulting in reduced regenerative response following PH. The persistent block of at least four weeks may promote preferential proliferation of transplanted hepatocytes in this milieu.

Hepatocyte transplantation is regarded as a promising option to correct hereditary metabolic liver disease. This study describes a novel method involving regional transient portal ischemia (RTPI) in combination with hepatic irradiation (IR) as a preparative regimen for hepatocyte transplantation. The right lobules of rat livers (45% of liver mass) were subjected to RTPI of 30-120 min. Liver specimens and serum samples were analyzed for transaminase levels, DNA damage, apoptosis, and proliferation. Repopulation experiments involved livers of dipeptidylpeptidase IV (DPPIV)-deficient rats preconditioned with RTPI (60-90 min) either with or without prior partial hepatic IR (25 Gy). After reperfusion intervals of 1 and 24 h, 12 million wild-type (DPPIV positive) hepatocytes were transplanted into recipient livers via the spleen. RTPI of 60-90 min caused limited hepatic injury through necrosis and induced a distinct regenerative response in the host liver. Twelve weeks following transplantation, small clusters of donor hepatocytes were detected within the portal areas. Quantitative analysis revealed limited engraftment of 0.79% to 2.95%, whereas control animals (sham OP) exhibited 4.16% (determined as relative activity of DPPIV when compared to wild-type liver). Repopulation was significantly enhanced (21.43%) when IR was performed prior to RTPI, optimum preconditioning settings being 90 min of ischemia and 1 h of reperfusion before transplantation. We demonstrate that RTPI alone is disadvantageous to donor cell engraftment, whereas the combination of IR with RTPI comprises an effective preparative regimen for liver repopulation. The method described clearly has potential for clinical application.

Near infrared fluorescence (NIRF) optical imaging is a technique particularly powerful when studying in vivo processes at the molecular level in preclinical animal models. We recently demonstrated liver irradiation under the additional stimulus of partial hepatectomy as being an effective primer in the rat liver repopulation model based on hepatocyte transplantation. The purpose of this study was to assess optical imaging and the feasibility of donor cell expansion tracking in vivo using a fluorescent probe. Livers of dipeptidylpeptidase IV (DPPIV)-deficient rats were preconditioned with irradiation. Four days later, a partial hepatectomy was performed and wild-type (DPPIV + ) hepatocytes were transplanted into recipient livers via the spleen. Repopulation by transplanted DPPIV + hepatocytes was detected in vivo with Cy5.5-conjugated DPPIV antibody using the eXplore Optix TM System (GE HealthCare). Results were compared with nontransplanted control animals and transplanted animals receiving nonspecific antibody. Optical imaging detected Cy5.5-specific fluorescence in the liver region of the transplanted animals, increasing in intensity with time, representing extensive host liver repopulation within 16 weeks following transplantation. A general pattern of donor cell multiplication emerged, with an initially accelerating growth curve and later plateau phase. In contrast, no specific fluorescence was detected in the control groups. Comparison with ex vivo immunofluorescence staining of liver sections confirmed the optical imaging results. Optical imaging constitutes a potent method of assessing the longitudinal kinetics of liver repopulation in the rat transplantation model. Our results provide a basis for the future development of clinical protocols for suitable fluorescent dyes and imaging technologies.

Hypofractionated radiotherapy is the mainstay of the current treatment for glioblastoma. However, the efficacy of radiotherapy is hindered by the high degree of radioresistance associated with glioma stem cells comprising a heterogeneous compartment of cell lineages differing in their phenotypic characteristics, molecular signatures, and biological responses to external signals. Reconstruction of radiation responses in glioma stem cells is necessary for understanding the biological and molecular determinants of glioblastoma radioresistance. To date, there is a paucity of information on the longitudinal outcomes of hypofractionated radiation in glioma stem cells. This study addresses long-term outcomes of hypofractionated radiation in human glioma stem cells by using a combinatorial approach integrating parallel assessments of the tumor-propagating capacity, stemness-associated properties, and array-based profiling of gene expression. The study reveals a broad spectrum of changes in the tumor-propagating capacity of glioma stem cells after radiation and finds association with proliferative changes at the onset of differentiation. Evidence is provided that parallel transcriptomic patterns and a cumulative impact of pathways involved in the regulation of apoptosis, neural differentiation, and cell proliferation underly similarities in tumorigenicity changes after radiation.

Background: As the majority of prostate cancers (PC) express estrogen receptors, we evaluated the combination of radiation and estrogenic stimulation (estrogen and genistein) on the radiosensitivity of PC cells in vitro.

The chorioallantoic membrane of fertilized chicken eggs in an early phase of breeding presents an approved test situation for the growth and treatment of human cancer cells.These models work due to the inoculation of cells into the membrane that stays within the egg shell during the time of investigation. In this study a modification of this model is presented. Samples of native tumors, rather than cell lines, are transplanted into the membrane and the body of the egg is taken out of the shell and placed in a plastic bowl. These modifications lead to an enhanced accessibility to the chorioallantoic membrane and the surrounding vessels thus facilitating intra venous access and application of pharmaceuticals and a focused radiotherapy. With the current modifications the embryo was kept alive and additionally, the vascularized tumor environment was preserved.

Background: Activation of Wnt/β-catenin signaling plays a central role in the development and progression of colorectal cancer (CRC). Previously, we demonstrated that the Wnt transcription factor TCF7L2 was overexpressed in primary rectal cancers that were resistant to chemoradiotherapy (CRT), and that TCF7L2 functionally mediates resistance of CRC to clinically relevant doses of CRT. However, it remained unclear whether the resistance was mediated by a TCF7L2 inherent mechanism or Wnt/β-catenin signaling in general. Methods: We silenced another key-component of canonical Wnt-signaling, CTNNB1 (β-catenin) in rectal cancer cell lines LS1034, SW480, and SW837 by RNAi. Afterwards cells were exposed to varying doses of irradiation (+/- 5 FU) to assess the influence of β-catenin on radiation response. Activation of Wnt-signaling in “normal” epithelial cells (retina pigment epithelial cells RPE) was achieved either by stimulation with Wnt-3A, or stable overexpression of non-degradable β-catenin (S33Y-mutated) and confirmed by a dual luciferase reporter assay. Changes in radio-(chemo-) sensitivity were analyzed again by a colony formation assay. SW1463 were repeatedly irradiated (68Gy) to establish an isogenic radio-resistant cell line. Gene-expression profiles, without or 6h after a single dose of 4Gy, of RPE cells expressing a control vector or overexpressing β-catenin and radioresistant or wildtype SW1463 cells were established using micro Arrays. Results: Silencing of CTNNB1 resulted in (chemo-) radiation-sensitization of all three CRC-cell lines. To further investigate the potential role of Wnt/β-catenin signaling in controlling therapeutic responsiveness, non-tumorigenic RPE cells were stimulated with Wnt-3A, which significantly increased resistance to CRT. This effect could be recapitulated by overexpression of β-catenin (S33Y-mut.), resulting in a significantly increased resistance to CRT. The effect could be rescued by siRNA mediated knockdown of β-catenin. Consistent with these findings, we observed higher expression levels of active (unphosphorylated) β-catenin as well as increased TCF reporter activity in SW1463 cells that were rendered radiation-resistant due to repeated IR treatment. Gene expression profiling of radioresistant and wildtype SW1463 as well as RPE cells overexpressing β-catenin or a control vector revealed significant transcriptomal changes. Most interestingly the resistant cells (radioresistant SW1463 and RPE overexpressing β-catenin) reacted with differential activation of metabolic, inflammatory, cell survival and cell cycle pathways to irradiation. Conclusion: Together, these findings strongly support the interpretation that Wnt/β-catenin signaling plays a central role in mediating resistance of CRC cells to CRT by deregulating essential pathways. Hence, pathway inhibition may represent a promising strategy to increase therapeutic responsiveness to CRT. Citation Format: Georg Emons, Melanie Spitzner, Sebastian Reineke, Noam Auslander, Frank Kramer, Margret Rave-Fraenk, Jochen Gaedcke, Michael Ghadimi, Thomas Ried, Marian Grade. Wnt/β-catenin signaling mediates resistance of colorectal cancer cell lines to chemoradiotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4760. doi:10.1158/1538-7445.AM2017-4760