angiopoietin In addition clinical data indicate a connection

In addition, clinical data indicate a connection between tp53 and mitochondrial function. Our data are in agreement with a prior cohort study of patients with Li Fraumeni syndrome (LFS), which is caused by the germline transmission of TP53 mutation (Wang et al., 2013). In this study, both lymphocytes and myoblasts from patients with LFS demonstrated significantly higher rates of baseline mitochondrial OCR, suggesting that TP53 played a significant role in global mitochondrial function. Finally, there is also clinical evidence linking tp53 mutation to dyserythropoeisis in myelodysplastic syndrome (MDS). Kulasekararaj et al. (2013) analyzed the TP53 mutation status in over 300 patients with MDS. Within the patient characteristics analysis, they found that MDS patients with mutated TP53 were almost 15 times more apt to be transfusion dependent versus those without TP53 mutations. It is not known whether this was due to haploinsufficiency of TP53 leading to reduced cell production or an increase in erythroid cell death, but it does provide evidence for a link between TP53 mutation and aberrant erythropoiesis (Kulasekararaj et al., 2013). Furthermore, it is known that MDS patients with TP53 mutations have a higher mortality rate and poorer response to treatment than MDS patients without TP53 mutations (Jadersten et al., 2011). In conclusion, we utilized the zebrafish as a model to demonstrate the contribution of Gata1+ erythroid angiopoietin to the oxidative stress response. We found that TP53 plays a key role in erythroid cells management of a Gata1+ pro-oxidant challenge. Mutation in tp53 allowed for basal mitochondrial respiration to occur at a significantly elevated rate, a contributing factor to the enhanced ROS and cell death we observed in tp53-mutant animals. This model allows us to observe the physiological responses to oxidative stress at the whole-organism level. Future work will focus on determining the specific mechanisms by which Tp53 can regulate mitochondrial function and how mutated tp53 dysregulates mitochondrial respiration, as well as the oxidative stress response.
Experimental Procedures
Author Contributions
Acknowledgments We gratefully thank the laboratory of Dr. Zon for sharing the vlad tepes zebrafish. Research reported in this publication was supported by the National Heart, Lung, and Blood Institute of the NIH under award number K08HL108998 (T.C.L.), ASH Junior Faculty Scholar Award (T.C.L.), the University of Minnesota Academic Health Center Seed Grant (T.C.L.), The Children\'s Cancer Research Fund (T.C.L.), and The Viking\'s Research Fund (T.C.L.).
Introduction Human bone marrow stromal cells (hBMSCs) are non-hematopoietic multipotent cells capable of differentiation into mesodermal cell types such as osteoblasts (OBs) and adipocytes (ADs) (Abdallah and Kassem, 2008). It is increasingly recognized that secreted factors have an important role in mediating hBMSC function to actively maintain homeostasis of skeletal tissue. In addition, secreted proteins mediate the observed therapeutic effects of hBMSCs on enhancing regeneration of skeletal (Hernigou et al., 2005), cardiac (Hare et al., 2009), dermal (Bey et al., 2010), and neural (Yamout et al., 2010) tissues. Characterizing the functions of proteins secreted by hBMSCs is a pre-requisite for understanding the mechanisms of their therapeutic effects and their role in tissue homeostasis in normal and disease states. We recently reported a profile of hBMSC-secreted factors at different stages of ex vivo OB differentiation using a quantitative proteomic analysis based on stable isotope labeling by amino acids in cell culture (Kristensen et al., 2012). Among the differentially regulated proteins during OB differentiation, we identified legumain as a secreted protein that has not been previously implicated in hBMSC biology. Legumain (also known as asparaginyl endopeptidase, AEP), encoded by the LGMN gene, is a broadly expressed lysosomal cysteine protease that is secreted as inactive prolegumain (56 kDa) and processed into enzymatically active 46 and 36 kDa forms, as well as a 17 kDa enzymatically inactive C-terminal fragment. Legumain directly regulates diverse physiological and pathological processes by remodeling tissue-specific targets (e.g., extracellular matrix [ECM] components, enzymes, receptors) (Chen et al., 2001; Clerin et al., 2008; Deryugina and Quigley, 2006; Ewald et al., 2008, 2011; Liu et al., 2003; Manoury et al., 1998; Mattock et al., 2010; Miller et al., 2011; Morita et al., 2007; Papaspyridonos et al., 2006; Sepulveda et al., 2009; Solberg et al., 2015). In addition, legumain indirectly contributes to atherosclerotic plaque instability through activation of cathepsin L in the arterial ECM (Clerin et al., 2008; Kitamoto et al., 2007; Mattock et al., 2010; Papaspyridonos et al., 2006). Surprisingly, the non-enzymatic 17 kDa C-terminal fragment is also biologically active and inhibits osteoclast differentiation through binding to an uncharacterized receptor (Choi et al., 1999, 2001).