The role of transient receptor potential vanilloid 2 channel in cardiac aging.

BACKGROUND: The aging heart is characterized by cellular and molecular changes leading to a decline in physiologic function and cardiac remodeling, specifically the development of myocyte hypertrophy and fibrosis. Transient receptor potential vanilloid 2 (TRPV2), a stretch-mediated channel and regulator of calcium homeostasis, plays a key role in the function and structure of the heart. TRPV2 also plays an important role in the adaptive and maladaptive compensatory mechanisms of the heart in response to pathologic and exercise-induced stress. Our current study seeks to elucidate the potential role of TRPV2 channels in the regulation of cardiac function in aging. METHODS: Wild-type (WT) and TRPV2 functional knockout (FKO) mice were aged out to various time points, and their cardiac function was measured using advanced echocardiography. Furthermore, we histologically analyzed the heart morphology to determine myocyte hypertrophy, the development of fibrosis and the relative expression of TRPV2. RESULTS: Our results demonstrate that even though TRPV2-FKO mice have impaired function at baseline, their cardiac function as measured via standard and advanced echocardiographic parameters (ejection fraction, cardiac output and circumferential strain) decreased less with aging in comparison with the WT group. Furthermore, there was less fibrosis and hypertrophy in the TRPV2-FKO group with aging in comparison with the WT. The expression of TRPV2 in the WT group did not significantly change with aging. CONCLUSIONS: TRPV2 functional deletion is compatible with aging and associated with a decreased development of myocyte hypertrophy and fibrosis. It may be an important target for prevention of age-induced cardiac remodeling.

Transient receptor potential vanilloid 2 function regulates cardiac hypertrophy via stretch-induced activation.

OBJECTIVE: Hypertension (increased afterload) results in cardiomyocyte hypertrophy leading to left ventricular hypertrophy and subsequently, heart failure with preserved ejection fraction. This study was performed to test the hypothesis that transient receptor potential vanilloid 2 subtype (TRPV2) function regulates hypertrophy under increased afterload conditions. METHODS: We used functional (pore specific) TRPV2 knockout mice to evaluate the effects of increased afterload-induced stretch on cardiac size and function via transverse aortic constriction (TAC) as well as hypertrophic stimuli including adrenergic and angiotensin stimulation via subcutaneous pumps. Wild-type animals served as control for all experiments. Expression and localization of TRPV2 was investigated in wild-type cardiac samples. Changes in cardiac function were measured in vivo via echocardiography and invasive catheterization. Molecular changes, including protein and real-time PCR markers of hypertrophy, were measured in addition to myocyte size. RESULTS: TRPV2 is significantly upregulated in wild-type mice after TAC, though not in response to beta-adrenergic or angiotensin stimulation. TAC-induced stretch stimulus caused an upregulation of TRPV2 in the sarcolemmal membrane. The absence of functional TRPV2 resulted in significantly reduced left ventricular hypertrophy after TAC, though not in response to beta-adrenergic or angiotensin stimulation. The decreased development of hypertrophy was not associated with significant deterioration of cardiac function. CONCLUSION: We conclude that TRPV2 function, as a stretch-activated channel, regulates the development of cardiomyocyte hypertrophy in response to increased afterload.

The transcription factor FOXF1 promotes prostate cancer by stimulating the mitogen-activated protein kinase ERK5.

Forkhead box F1 (FOXF1) is a stromal transcription factor that is not expressed in epithelial cells of normal prostate tissue. The role of FOXF1 in cancer is conflicting; its loss in some cancers suggests a tumor suppressive function, but its abundance in others is associated with protumorigenic and metastatic traits. Extracellular signal-regulated kinase 5 (ERK5) is associated with advanced-stage prostate adenocarcinoma (PCa) in patients. We detected a population of FOXF1-positive tumor cells in aggressive mouse and human PCa. Using two murine orthotopic models of PCa, we found that overexpression of FOXF1 in Myc-CaP and TRAMP prostate tumor cells induced tumor growth in the prostate and progression to peritoneal metastasis. Increased growth of FOXF1-positive prostate tumors was associated with increased phosphorylation of ERK5, a member of the mitogen-activated protein kinase (MAPK) family. FOXF1 transcriptionally induced and directly bound to promoter regions of genes encoding the kinases MAP3K2 and WNK1, which promoted the phosphorylation and activation of ERK5. Knockdown of ERK5 or both MAP3K2 and WNK1 in FOXF1-overexpressing PCa cells reduced cell proliferation in culture and suppressed tumor growth and tumor metastasis when implanted into mice. In human tumors, FOXF1 expression correlated positively with that of MAP3K2 and WNK1 Thus, in contrast to some tumors where FOXF1 may function as a tumor suppressor, FOXF1 promotes prostate tumor growth and progression by activating ERK5 signaling. Our results also indicate that ERK5 may be a new therapeutic target in patients with FOXF1-positive PCa.

Transient Receptor Potential Vanilloid 2 Regulates Myocardial Response to Exercise.

The myocardial response to exercise is an adaptive mechanism that permits the heart to maintain cardiac output via improved cardiac function and development of hypertrophy. There are many overlapping mechanisms via which this occurs with calcium handling being a crucial component of this process. Our laboratory has previously found that the stretch sensitive TRPV2 channels are active regulators of calcium handling and cardiac function under baseline conditions based on our observations that TRPV2-KO mice have impaired cardiac function at baseline. The focus of this study was to determine the cardiac function of TRPV2-KO mice under exercise conditions. We measured skeletal muscle at baseline in WT and TRPV2-KO mice and subjected them to various exercise protocols and measured the cardiac response using echocardiography and molecular markers. Our results demonstrate that the TRPV2-KO mouse did not tolerate forced exercise although they became increasingly exercise tolerant with voluntary exercise. This occurs as the cardiac function deteriorates further with exercise. Thus, our conclusion is that TRPV2-KO mice have impaired cardiac functional response to exercise.

SPDEF inhibits prostate carcinogenesis by disrupting a positive feedback loop in regulation of the Foxm1 oncogene.

SAM-pointed domain-containing ETS transcription factor (SPDEF) is expressed in normal prostate epithelium. While its expression changes during prostate carcinogenesis (PCa), the role of SPDEF in prostate cancer remains controversial due to the lack of genetic mouse models. In present study, we generated transgenic mice with the loss- or gain-of-function of SPDEF in prostate epithelium to demonstrate that SPDEF functions as tumor suppressor in prostate cancer. Loss of SPDEF increased cancer progression and tumor cell proliferation, whereas over-expression of SPDEF in prostate epithelium inhibited carcinogenesis and reduced tumor cell proliferation in vivo and in vitro. Transgenic over-expression of SPDEF inhibited mRNA and protein levels of Foxm1, a transcription factor critical for tumor cell proliferation, and reduced expression of Foxm1 target genes, including Cdc25b, Cyclin B1, Cyclin A2, Plk-1, AuroraB, CKS1 and Topo2alpha. Deletion of SPDEF in transgenic mice and cultures prostate tumor cells increased expression of Foxm1 and its target genes. Furthermore, an inverse correlation between SPDEF and Foxm1 levels was found in human prostate cancers. The two-gene signature of low SPDEF and high FoxM1 predicted poor survival in prostate cancer patients. Mechanistically, SPDEF bound to, and inhibited transcriptional activity of Foxm1 promoter by interfering with the ability of Foxm1 to activate its own promoter through auto-regulatory site located in the -745/-660 bp Foxm1 promoter region. Re-expression of Foxm1 restored cellular proliferation in the SPDEF-positive cancer cells and rescued progression of SPDEF-positive tumors in mouse prostates. Altogether, SPDEF inhibits prostate carcinogenesis by preventing Foxm1-regulated proliferation of prostate tumor cells. The present study identified novel crosstalk between SPDEF tumor suppressor and Foxm1 oncogene and demonstrated that this crosstalk is required for tumor cell proliferation during progression of prostate cancer in vivo.

Foxm1 expression in prostate epithelial cells is essential for prostate carcinogenesis.

The treatment of advanced prostate cancer (PCa) remains a challenge. Identification of new molecular mechanisms that regulate PCa initiation and progression would provide targets for the development of new cancer treatments. The Foxm1 transcription factor is highly up-regulated in tumor cells, inflammatory cells, and cells of tumor microenvironment. However, its functions in different cell populations of PCa lesions are unknown. To determine the role of Foxm1 in tumor cells during PCa development, we generated two novel transgenic mouse models, one exhibiting Foxm1 gain-of-function and one exhibiting Foxm1 loss-of-function under control of the prostate epithelial-specific Probasin promoter. In the transgenic adenocarcinoma mouse prostate (TRAMP) model of PCa that uses SV40 large T antigen to induce PCa, loss of Foxm1 decreased tumor growth and metastasis. Decreased prostate tumorigenesis was associated with a decrease in tumor cell proliferation and the down-regulation of genes critical for cell proliferation and tumor metastasis, including Cdc25b, Cyclin B1, Plk-1, Lox, and Versican. In addition, tumor-associated angiogenesis was decreased, coinciding with reduced Vegf-A expression. The mRNA and protein levels of 11ß-Hsd2, an enzyme playing an important role in tumor cell proliferation, were down-regulated in Foxm1-deficient PCa tumors in vivo and in Foxm1-depleted TRAMP C2 cells in vitro. Foxm1 bound to, and increased transcriptional activity of, the mouse 11ß-Hsd2 promoter through the -892/-879 region, indicating that 11ß-Hsd2 was a direct transcriptional target of Foxm1. Without TRAMP, overexpression of Foxm1 either alone or in combination with inhibition of a p19(ARF) tumor suppressor caused a robust epithelial hyperplasia, but was insufficient to induce progression from hyperplasia to PCa. Foxm1 expression in prostate epithelial cells is critical for prostate carcinogenesis, suggesting that inhibition of Foxm1 is a promising therapeutic approach for prostate cancer chemotherapy.

Lumican reduces tumor growth via induction of fas-mediated endothelial cell apoptosis.

Matrikines are important components of tumor microenvironments that integrate communication between extracellular matricies and membrane-bound receptors thereby regulating cellular behaviors. One such matrikine that is differentially expressed in cancer microenvironments is the extracellular matrix protein lumican; however its precise role in cancer remains ambiguous. To study the effects of lumican on cancer cells, we created lumican-overexpressing cell lines from murine fibrosarcoma (MCA102) and pancreatic adenocarcinoma (Pan02) cells. Lumican overexpression in Pan02 cells increased invasiveness, decreased soft agar colony size, and increased proliferation. Conversely in MCA102 cells, lumican decreased invasiveness, increased soft agar colony size, but did not influence proliferation. In contrast to these pleiotropic in vitro results, lumican overexpression within the in vivo tumor microenvironment produced uniformly smaller tumors. Importantly, reduced tumor size was correlated with reduced vascular density. Consistent with lumican's proposed anti-angiogenic activity, lumican increased endothelial cell apoptosis. Importantly, lumican was previously shown to influence Fas expression and our results show that lumican enhanced Fas mediated endothelial cell apoptosis although we were unable to detect any difference in Fas or Fas ligand expression between lumican-overexpressing and control cells. Interestingly, lumican had no effect on MCA102 apoptosis, suggesting that the observed reduction in tumor size is specifically due to endothelial cell apoptosis rather than a direct effect on the cancerous cells themselves. Therefore, this study is the first to demonstrate a causal relationship between tumor reduction and lumican's effect on angiogenesis as opposed to an effect on the cancerous cells themselves.