Background: Myocardial infarction is one of the leading causes of morbidity and mortality worldwide, triggering irreversible myocardial cell damage and heart failure. The role of low-density lipoprotein receptor-related proteins 5 and 6 (LRP5/6) as coreceptors of the Wnt/β-catenin pathway in the adult heart remain unknown. Insulin-like growth factor binding protein 4 and dickkopf-related protein 1 (Dkk1) are 2 secreted LRP5/6 binding proteins that play a crucial role in heart development through preventing Wnt/β-catenin pathway activation. However, their roles in the adult heart remain unexplored. Methods: To understand the role of LRP5/6 and β-catenin in the adult heart, we constructed conditional cardiomyocyte-specific LRP5/6 and β-catenin knockout mice and induced surgical myocardial infarction. We also directly injected recombinant proteins of insulin-like growth factor binding protein 4 and Dkk1 into the heart immediately following myocardial infarction to further examine the mechanisms through which these proteins regulate LRP5/6 and β-catenin. Results: Deletion of LRP5/6 promoted cardiac ischemic insults. Conversely, deficiency of β-catenin, a downstream target of LRP5/6, was beneficial in ischemic injury. It is interesting to note that although both insulin-like growth factor binding protein 4 and Dkk1 are secreted Wnt/β-catenin pathway inhibitors, insulin-like growth factor binding protein 4 protected the ischemic heart by inhibiting β-catenin, whereas Dkk1 enhanced the injury response mainly through inducing LRP5/6 endocytosis and degradation. Conclusions: Our findings reveal previously unidentified dual roles of LRP5/6 involved in the cardiomyocyte response to ischemic injury. These findings suggest new therapeutic strategies in ischemic heart disease by fine-tuning LRP5/6 and β-catenin signaling within the Wnt/β-catenin pathway.

How Wnt signalling including canonical and non-canonical pathways are initiated at the cell surface is not completely understood. Here we report that Wnt receptor Frizzled (Frz) and theco-receptors LRP5 and LRP6 (LRP5/6) directly interact with each other and this interaction is regulated by the LRP6 ectodomain. Importantly, through direct binding to Frz, LRP5/6 are able to prevent Frz-regulated non-canonical pathway activation and further non-canonical pathway-mediated tumour metastasis. Knockdown of endogenous LRP5/6 promotes otherwise-nonaggressive tumour cells to migrate in vitro, whereas a soluble recombinant protein of LRP6 ectodomain suppresses migration and metastasis of otherwise-aggressive tumour cells in vitro and in vivo. Furthermore, the expression level of membrane LRP5/6 correlates inversely with metastasis in mouse and human breast cancer. Our study suggests a previously unrecognized mode of receptor interaction, revealing the mechanism of LRP5/6 in inhibition of non-canonical pathway, and a possible clinical use of the LRP6 ectodomain to impede metastasis.

Pathological cardiac hypertrophy is a hallmark of various cardiovascular diseases (CVD) including chronic heart failure (HF) and an important target for the treatment of these diseases. Aberrant activation of Angiotensin II (Ang II)/AT1R signaling pathway is one of the main triggers of cardiac hypertrophy, which further gives rise to excessive inflammation that is mediated by the key transcription factor NF-κB. Resveratrol (REV) is a natural polyphenol with multiple anti-inflammatory and anti-oxidative effects, however the ability of REV in preventing Ang II-induced cardiac hypertrophy in combination with NF-κB signaling activation remains unclear. Murine models of cardiac hypertrophy was conducted via implantation of Ang II osmotic pumps. Primary neonatal rat cardiomyocyte and heart tissues were examined to determine the effect and underlying mechanism of REV in preventing Ang II-induced cardiac hypertrophy. Administrations of REV significantly prevented Ang II-induced cardiac hypertrophy, as well as robustly attenuated Ang II-induced cardiac fibrosis, and cardiac dysfunction. Furthermore, REV not only directly prevented Ang II/AT1R signal transductions, but also prevented Ang II-induced expressions of pro-inflammatory cytokines and activation of NF-κB signaling pathway. Our study provides important new mechanistic insight into the cardioprotective effects of REV in preventing Ang II-induced cardiac hypertrophy via inhibiting adverse NF-κB signaling activation. Our findings further suggest the therapeutic potential of REV as a promising drug for the treatment of cardiac hypertrophy and heart failure.

Purpose: Lung metastasis is an important cause of breast cancer-related deaths, in which SDF-1/CXCR4 signaling pathway plays a critical role. Single transmembrane protein LRP6 is viewed as an oncogene via activating Wnt/β-catenin signaling pathway. Our work aims to investigate the relationship between SDF-1/CXCR4 and LRP6 in breast cancer lung metastasis. Experimental Design: We examined the expressions and functions of SDF-1/CXCR4 and LRP6 as well as their relationship in breast cancer in vitro and in vivo. Results: LRP6 ectodomain (LRP6N) directly bound to CXCR4 and competitively prevented SDF-1 binding to CXCR4. LRP6N prevented SDF-1/CXCR4-induced metastasis to lung and prolonged survival in mice bearing breast tumors, whereas LRP6 knockdown activated SDF-1/CXCR4 signal transduction and promoted lung metastasis and tumor death. Furthermore, breast cancer patients with high CXCR4 expression had poor prognosis, which was exacerbated by low LRP6 expression but improved by high LRP6 expression. Interestingly, a secreted LRP6N was found in the serum of mice and humans, which was downregulated by the onset of cancer metastasis in both mice bearing breast cancer, as well as in breast cancer patients. Conclusions: LRP6N might be a promising diagnostic marker for the early detection of breast cancer metastasis, as well as an inhibitor of SDF-1/CXCR4-induced breast cancer metastasis. LRP6N also provides an interesting link between Wnt signaling and SDF-1/CXCR4 signaling, the two key pathways involved in cancer development.

Background: LRP5/6 are co-receptors in Wnt/β-catenin pathway. Recently, we discovered multiple β-catenin independent functions of LRP5/6 in tumor cells and in the diseased heart. Nucleoporin 37 (NUP37) is an important component of the nuclear pore complex (NPC), whose elevated expression is associated with worsened prognosis in liver cancer. Previous studies have shown that NUP37 interacted with YAP and activated YAP/TEAD signaling in liver cancer. Our preliminary findings showed a nuclear location of LRP5. We thus tested the hypothesis that LRP5 may act as a genuine regulator of YAP/TEAD signaling via modulating NUP37 in a β-catenin-independent way. Methods: We performed siRNA knockdown of LRP5, LRP6, or β-catenin in liver cancer HepG2 cells to determine the effect on tumor cell proliferation. Protein expressions and interaction between LRP5 and NUP37 were determined using immunoprecipitation and western blot analyses. Results: HepG2 cell proliferation was markedly inhibited by knockdown of LRP5 but not LRP6 or β-catenin, suggesting that LRP5 has a specific, β-catenin-independent role in inhibiting HepG2 cell proliferation. Knockdown of NUP37 by siRNA inhibited the proliferation of HepG2 cells, whereas overexpression of NUP37 reversed the decrease in cell proliferation induced by LRP5 knockdown. Immunoprecipitation assays confirmed that LRP5 bound to NUP37. Furthermore, LRP5 overexpression restored NUP37 knockdown-induced downregulation of YAP/TEAD pathway. Conclusions: LRP5 deletion attenuates cell proliferation via destabilization of NUP37, in a β-catenin-independent manner. LRP5 therefore acts as a genuine regulator of YAP/TEAD signaling via maintaining the integrity of the NPC, and implicates a therapeutic strategy in targeting LRP5 for inhibiting liver cancer cell proliferation.