Fig. 7.

SPRR2B is significantly enriched in the failing human heart and positively correlates with promitotic factors in human HF fibroblasts. (A) qRT-PCR was used to evaluate SPRR2B expression in left ventricle tissue isolated HF patients or healthy hearts. n = 16 (Healthy), 15 (HF). ND, not detected. (B) Immunohistochemistry of representative sections from failing or healthy hearts costained for WGA (white), SPRR2B (green), and VIMENTIN (VIM, red). DAPI (blue) stains nuclei. SPRR2B is associated with vimentin-positive cells in the failing heart, indicated by white arrows. (Scale bar: 25 μm.) (C) qRT-PCR was used to evaluate the expression of SPRR2B and genes encoding myofibroblast markers in human CFs isolated from healthy or failing (HF) hearts (n = 3 HF and one healthy isolate). (D) qRT-PCR was used to evaluate the expression of SPRR2B and myofibroblast markers in healthy human CFs treated with indicated combinations of TGF-β1 (10 ng/mL), IGF1 (100 ng/mL), and H₂O₂ (25 μM) (n = 3). (E) qRT-PCR was used to evaluate the expression of SPRR2B and mitotic regulators in human HF CFs treated with vehicle or IGF1/H₂O₂. (F) CyQuant dye incorporation to measure proliferation of human HF CFs treated with vehicle or IGF1/H₂O₂. All qRT-PCR data normalized to Gapdh and analyzed by one-way ANOVA (n = 3, unless indicated). CyQuant data analyzed by unpaired Student’s t test (n= 3). All data represent mean ± SEM. *P < 0.05; **P < 0.01. (G) Model highlighting the role of SPRR2B in regulating cell cycle progression in CFs. Heart disease (in vivo) or TGF-β1/ROS (in vitro) induce, while exercise (in vivo) or IGF1 (in vitro) repress SPRR2B gene expression in CFs. Phosphorylation of SPRR2B facilitates interaction with USP7/MDM2, leading to MDM2 accumulation and degradation of the nuclear p53 pool, relieving constraints on cell cycle progression and promoting fibrosis in heart disease.