Elevated SOCS3 and altered IL-6 signaling is associated with age-related human muscle stem cell dysfunction.

Aging is associated with increased circulating interleukin-6 (IL-6) and a reduced myogenic capacity, marked by reduced muscle stem cell [satellite cell (SC)] activity. Although IL-6 is important for normal SC function, it is unclear whether elevated IL-6 associated with aging alters SC function. We hypothesized that mild chronically elevated IL-6 would be associated with a blunted SC response through altered IL-6 signaling and elevated suppressor of cytokine signaling-3 (SOCS3) in the elderly. Nine healthy older adult men (OA; 69.6 ± 3.9 yr) and 9 young male controls (YC; 21. 3 ± 3.1 yr) completed 4 sets of 10 repetitions of unilateral leg press and knee extension (75% of 1-RM). Muscle biopsies and blood were obtained before and 3, 24, and 48 h after exercise. Basal SC number was 33% lower in OA vs. YC, and the response was blunted in OA. IL-6(+)/Pax7(+) cells demonstrated a divergent response in OA, with YC increasing to 69% at 3 h and peaking at 24 h (72%), while IL-6(+)/Pax7(+) cells were not increased until 48 h in OA (61%). Type II fiber-associated phosphorylated signal transducer and activator of transcription (pSTAT3)(+)/Pax7(+) cells demonstrated a similar delay in OA, not increasing until 48 h (vs. 3 h in YC). SOCS3 protein was 86% higher in OA. These data demonstrate an age-related impairment in normal SC function that appears to be influenced by SOCS3 protein and delayed induction of IL-6 and pSTAT3 in the SCs of OA. Collectively, these data suggest dysregulated IL-6 signaling as a consequence of aging contributes to the blunted muscle stem cell response.

Satellite cell number and cell cycle kinetics in response to acute myotrauma in humans: immunohistochemistry versus flow cytometry.

In humans, muscle satellite cell (SC) enumeration is an important measurement used to determine the myogenic response to various stimuli. To date, the standard practice for enumeration is immunohistochemistry (IHC) using antibodies against common SC markers (Pax7, NCAM). Flow cytometry (FC) analysis may provide a more rapid and quantitative determination of changes in the SC pool with potential for additional analysis not easily achievable with standard IHC. In this study, FC analysis revealed that the number of Pax7(+) cells per milligram isolated from 50 mg of fresh tissue increased 36% 24 h after exercise-induced muscle injury (300 unilateral maximal eccentric contractions). IHC analysis of Pax7 and neural cell adhesion molecule (NCAM) appeared to sufficiently and similarly represent the expansion of SCs after injury (28-36% increase). IHC and FC data illustrated that Pax7 was the most widely expressed SC marker in muscle cross-sections and represented the majority of positive cells, while NCAM was expressed to a lesser degree. Moreover, FC and IHC demonstrated a similar percentage change 24 h after injury (36% increase, Pax7; 28% increase, NCAM). FC analysis of isolated SCs revealed that the number of Pax7(+) cells per milligram in G(2)/M phase of the cell cycle increased 202% 24 h after injury. Number of cells per milligram in G(0)/G(1) and cells in S-phase increased 32% and 59% respectively. Here we illustrate the use of FC as a method for enumerating SC number on a per milligram tissue basis, providing a more easily understandable relation to muscle mass (vs. percentage of myonuclei or per myofibre). Although IHC is a powerful tool for SC analysis, FC is a fast, reliable and effective method for SC quantification as well as a more informative method for cell cycle kinetics of the SC population in humans.

CD38-NAD+Axis Regulates Immunotherapeutic Anti-Tumor T Cell Response.

Heightened effector function and prolonged persistence, the key attributes of Th1 and Th17 cells, respectively, are key features of potent anti-tumor T cells. Here, we established ex vivo culture conditions to generate hybrid Th1/17 cells, which persisted long-term in vivo while maintaining their effector function. Using transcriptomics and metabolic profiling approaches, we showed that the enhanced anti-tumor property of Th1/17 cells was dependent on the increased NAD+-dependent activity of the histone deacetylase Sirt1. Pharmacological or genetic inhibition of Sirt1 activity impaired the anti-tumor potential of Th1/17 cells. Importantly, T cells with reduced surface expression of the NADase CD38 exhibited intrinsically higher NAD+, enhanced oxidative phosphorylation, higher glutaminolysis, and altered mitochondrial dynamics that vastly improved tumor control. Lastly, blocking CD38 expression improved tumor control even when using Th0 anti-tumor T cells. Thus, strategies targeting the CD38-NAD+ axis could increase the efficacy of anti-tumor adoptive T cell therapy.

Discovery of Stromal Regulatory Networks that Suppress Ras-Sensitized Epithelial Cell Proliferation.

Mesodermal cells signal to neighboring epithelial cells to modulate their proliferation in both normal and disease states. We adapted a Caenorhabditis elegans organogenesis model to enable a genome-wide mesodermal-specific RNAi screen and discovered 39 factors in mesodermal cells that suppress the proliferation of adjacent Ras pathway-sensitized epithelial cells. These candidates encode components of protein complexes and signaling pathways that converge on the control of chromatin dynamics, cytoplasmic polyadenylation, and translation. Stromal fibroblast-specific deletion of mouse orthologs of several candidates resulted in the hyper-proliferation of mammary gland epithelium. Furthermore, a 33-gene signature of human orthologs was selectively enriched in the tumor stroma of breast cancer patients, and depletion of these factors from normal human breast fibroblasts increased proliferation of co-cultured breast cancer cells. This cross-species approach identified unanticipated regulatory networks in mesodermal cells with growth-suppressive function, exposing the conserved and selective nature of mesodermal-epithelial communication in development and cancer.

Blocking TCR restimulation induced necroptosis in adoptively transferred T cells improves tumor control.

Advancements in adoptive cell transfer therapy (ACT) has led to the use of T cells engineered with tumor specific T cell receptors, which after rapid expansion can be obtained in sufficient numbers for treating patients. However, due to massive proliferation these cells are close to replicative senescence, exhibit exhausted phenotype, and also display increased susceptibility to activation induced cell death. We have previously shown that tumor reactive T cells undergo caspase-independent cell death upon TCR restimulation with cognate antigen, which involves reactive oxygen species and c-jun N-terminal kinase. Herein, we show that a large fraction of the human melanoma epitope tyrosinase reactive TCR transduced T cells that exhibit effector memory (TEM) phenotype and undergo programmed necrosis, or necroptosis, upon TCR restimulation. As compared to the T central memory (TCM) subsets, the TEM subset displayed an increased expression of genes involved in necroptotic cell death, and a necrotic phenotype upon TCR restimulation as confirmed by electron microscopy. Higher expression of receptor-interacting kinases (RIPK) that mediate necroptosis was also observed in the TEM fraction. Further, the TEM cells were rescued from undergoing necroptosis when pretreated with necroptotic inhibitor NecroX2 before TCR restimulation. Importantly, NecroX2 pretreated tumor reactive T cells also exhibited better tumor control and increased in vivo persistence when adoptively-transferred to treat subcutaneously established murine melanoma B16-F10. Thus, it is likely that the outcome of ACT could be vastly improved by interfering with the necroptotic cell death pathway in activated tumor reactive T cells used in immunotherapy.

IL-6 induced STAT3 signalling is associated with the proliferation of human muscle satellite cells following acute muscle damage.

BACKGROUND: Although the satellite cell (SC) is a key regulator of muscle growth during development and muscle adaptation following exercise, the regulation of human muscle SC function remains largely unexplored. STAT3 signalling mediated via interleukin-6 (IL-6) has recently come to the forefront as a potential regulator of SC proliferation. The early response of the SC population in human muscle to muscle-lengthening contractions (MLC) as mediated by STAT3 has not been studied. METHODOLOGY/PRINCIPAL FINDINGS: Twelve male subjects (21±2 y; 83±12 kg) performed 300 maximal MLC of the quadriceps femoris at 180°â€¢s(-1) over a 55° range of motion with muscle samples (vastus lateralis) and blood samples (antecubital vein) taken prior to exercise (PRE), 1 hour (T1), 3 hours (T3) and 24 hours (T24) post-exercise. Cytoplasmic and nuclear fractions of muscle biopsies were purified and analyzed for total and phosphorylated STAT3 (p-STAT3) by western blot. p-STAT3 was detected in cytoplasmic fractions across the time course peaking at T24 (p<0.01 vs. PRE). Nuclear total and p-STAT3 were not detected at appreciable levels. However, immunohistochemical analysis revealed a progressive increase in the proportion of SCs expressing p-STAT3 with ∼60% of all SCs positive for p-STAT3 at T24 (p<0.001 vs. PRE). Additionally, cMyc, a STAT3 downstream gene, was significantly up-regulated in SCs at T24 versus PRE (p<0.05). Whole muscle mRNA analysis revealed induction of the STAT3 target genes IL-6, SOCS3, cMyc (peaking at T3, p<0.05), IL-6Rα and GP130 (peaking at T24, p<0.05). In addition, Myf5 mRNA was up-regulated at T24 (p<0.05) with no appreciable change in MRF4 mRNA. CONCLUSIONS/SIGNIFICANT FINDINGS: We demonstrate that IL-6 induction of STAT3 signaling occurred exclusively in the nuclei of SCs in response to MLC. An increase in the number of cMyc+ SCs indicated that human SCs were induced to proliferate under the control of STAT3 signaling.