Bone integrity depends on a finely tuned balance between bone synthesis by osteoblasts and resorption by osteoclasts. The secretion capacity of mature osteoblasts requires strict control of proteostasis. Endoplasmic reticulum-associated degradation (ERAD) prevents the accumulation of unfolded ER proteins via dislocation to the cytosol and degradation by the proteasome. The ER membrane protein, homocysteine-inducible endoplasmic reticulum protein with ubiquitin-like domain 1 (HERPUD1), is a key component of the ERAD multiprotein complex which helps to stabilize the complex and facilitate the efficient degradation of unfolded proteins. HERPUD1 expression is strongly up-regulated by the unfolded protein response and cellular stress. The aim of the current study was to establish whether HERPUD1 and ERAD play roles in osteoblast differentiation and maturation. We evaluated preosteoblastic MC3T3-E1 cell and primary rat osteoblast differentiation by measuring calcium deposit levels, alkaline phosphatase activity, and runt-related transcription factor 2 and osterix expression. We found that ERAD and proteasomal degradation were activated and that HERPUD1 expression was increased as osteoblast differentiation progressed. The absence of HERPUD1 blocked osteoblast mineralization in vitro and significantly reduced alkaline phosphatase activity. In contrast, HERPUD1 overexpression activated the osteoblast differentiation program. Our results demonstrate that HERPUD1 and ERAD are important for the activation of the osteoblast maturation program and may be useful new targets for elucidating bone physiology.-Américo-Da-Silva, L., Diaz, J., Bustamante, M., Mancilla, G., Oyarzún, I., Verdejo, H. E., Quiroga, C. A new role for HERPUD1 and ERAD activation in osteoblast differentiation and mineralization.

Hypertension (HTN) is a public health concern and a major preventable cause of cardiovascular disease (CVD). When uncontrolled, HTN may lead to adverse cardiac remodeling, left ventricular hypertrophy, and ultimately, heart failure. Regular aerobic exercise training exhibits blood pressure protective effects, improves myocardial function, and may reverse pathologic cardiac hypertrophy. These beneficial effects depend at least partially on improved mitochondrial function, decreased oxidative stress, endothelial dysfunction, and apoptotic cell death, which supports the general recommendation of moderate exercise in CVD patients. However, most of these mechanisms have been described on healthy individuals; the effect of moderate exercise on HTN subjects at a cellular level remain largely unknown. We hypothesized that hypertension in adult spontaneously hypertensive rats (SHRs) reduces the mitochondrial response to moderate exercise in the myocardium. Methods: Eight-month-old SHRs and their normotensive control—Wistar-Kyoto rats (WKYR)—were randomly assigned to moderate exercise on a treadmill five times per week with a running speed set at 10 m/min and 15° inclination. The duration of each session was 45 min with a relative intensity of 70–85% of the maximum O 2 consumption for a total of 8 weeks. A control group of untrained animals was maintained in their cages with short sessions of 10 min at 10 m/min two times per week to maintain them accustomed to the treadmill. After completing the exercise protocol, we assessed maximum exercise capacity and echocardiographic parameters. Animals were euthanized, and heart and muscle tissue were harvested for protein determinations and gene expression analysis. Measurements were compared using a nonparametric ANOVA (Kruskal-Wallis), with post-hoc Dunn's test. Results: At baseline, SHR presented myocardial remodeling evidenced by left ventricular hypertrophy (interventricular septum 2.08 ± 0.07 vs. 1.62 ± 0.08 mm, p < 0.001), enlarged left atria (0.62 ± 0.1 mm vs. 0.52 ± 0.1, p = 0.04), and impaired diastolic function (E/A ratio 2.43 ± 0.1 vs. 1.56 ± 0.2) when compared to WKYR. Moderate exercise did not induce changes in ventricular remodeling but improved diastolic filling pattern (E/A ratio 2.43 ± 0.1 in untrained SHR vs. 1.89 ± 0.16 trained SHR, p < 0.01). Histological analysis revealed increased myocyte transversal section area, increased Myh7 (myosin heavy chain 7) expression, and collagen fiber accumulation in SHR-control hearts. While the exercise protocol did not modify cardiac size, there was a significant reduction of cardiomyocyte size in the SHR-exercise group. Conversely, titin expression increased only WYK-exercise animals but remained unchanged in the SHR-exercise group. Mitochondrial response to exercise also diverged between SHR and WYKR: while moderate exercise showed an apparent increase in mR...

Galectin-3 (gal-3) is a β-galactoside-binding protein used as a prognostic biomarker in chronic heart failure (CHF) patients. Genetic and pharmacologic studies show that gal-3 is required for cardiac remodeling in animal models of CHF, suggesting an active role for gal-3 in the progression of the disease, but the mechanism involved is largely unknown. We assessed the hypothesis that gal-3 induces cardiac remodeling, causing both cardiomyocyte hypertrophy and fibroblasts activation through a mechanism involving intercellular communication. As a model, we used neonatal rat ventricular cardiomyocytes (NRVM), and fibroblasts (NRVF) stimulated with recombinant gal-3. We assessed cell death and proliferation by flow cytometry and MTT assays. To elucidate the signaling pathways involved, we quantified relative changes in protein levels by Western blot. To determine cell size and sarcomerization, we used confocal microscopy. Changes in mRNA and microRNA expression were analyzed by qPCR. Our results show that gal-3 does not induce hypertrophy or sarcomerization on isolated NRVM culture. On the other hand, NRVF treated with gal-3 exhibit an increase in ERK1/2 (n=3, p<0.05) and AKT (n=3, p<0.05) phosphorylation, as well as a marked increase in cell proliferation (n=4, p<0.05), without changes in αSMA and collagen. Interestingly, gal-3 increased tgfb1 expression in cardiac fibroblasts (n=5, p<0.05) and induced an increase of miR-21 and miR-23a levels in the culture media (15- and 6-folds over basal, respectively, n=4, p<0.05). To test a possible paracrine communication between cardiomyocytes and fibroblasts, we stimulated NRVM with fibroblast-derived, gal-3-stimmulated conditioned medium. Our results show that in this condition there is an increase in both cardiac remodeling markers (Nppa and Myh7), as well as cardiomyocyte area. In conclusion, gal-3 activates pro-survival and proliferation signaling pathways in cardiac fibroblasts without a direct effect on cardiomyocytes. However, gal-3 can induce cardiomyocyte hypertrophy by a mechanism involving paracrine communication between fibroblasts and myocytes, which likely includes TGFβ1 and the hypertrophy-related miR-21 and miR-23a.