Beta-Sitosterol Alters Collagen Distribution in Prostate Fibroblasts.

Herbal supplements containing several types of plant sterols, vitamins, and minerals, are marketed for prostate health. In the majority of these supplements, the most abundant plant sterol is saw palmetto extract or its' principal component, beta-sitosterol. In terms of prostate health, previous work almost exclusively focused on the effects of beta-sitosterol on prostatic epithelium, with little attention paid to the effects on prostatic stroma. This omission is a concern, as the abnormal accumulation of collagen, or fibrosis, of the prostatic stroma has been identified as a factor contributing to lower urinary tract symptoms and dysfunction in aging men. To address whether beta-sitosterol may be promoting prostatic fibrosis, immortalized and primary prostate stromal fibroblasts were subjected to immunoblotting, immunofluorescence, qRT-PCR, ELISA, and image quantitation and analysis techniques to elucidate the effects of beta-sitosterol on cell viability and collagen expression and cellular localization. The results of these studies show that beta-sitosterol is nontoxic to prostatic fibroblasts and does not stimulate collagen production by these cells. However, beta-sitosterol alters collagen distribution and sequesters collagen within prostatic fibroblasts, likely in an age-dependent manner. This is a significant finding as prostate health supplements are used predominantly by middle aged and older men who may, then, be affected disproportionately by these effects.

The IL-4/IL-13 signaling axis promotes prostatic fibrosis.

BACKGROUND: Lower urinary tract symptoms (LUTS) are a costly and pervasive medical problem for millions of aging men. Recent studies have showed that peri-urethral tissue fibrosis is an untreated pathobiology contributing to LUTS. Fibrosis results from excessive extracellular matrix deposition which increases transition zone and peri-urethral tissue stiffness and compromises prostatic urethral flexibility and compliance, producing urinary obstructive symptoms. Inflammatory cells, including neutrophils, macrophages, and T-lymphocytes, secrete a medley of pro-fibrotic proteins into the prostatic microenvironment, including IFNγ, TNFα, CXC-type chemokines, and interleukins, all of which have been implicated in inflammation-mediated fibrosis. Among these, IL-4 and IL-13 are of particular interest because they share a common signaling axis that, as shown here for the first time, promotes the expression and maintenance of IL-4, IL-13, their cognate receptors, and ECM components by prostate fibroblasts, even in the absence of immune cells. Based on studies presented here, we hypothesize that the IL-4/IL-13 axis promotes prostate fibroblast activation to ECM-secreting cells. METHODS: N1 or SFT1 immortalized prostate stromal fibroblasts were cultured and treated, short- or long-term, with pro-fibrotic proteins including IL-4, IL-13, TGF-ß, TNF-α, IFNγ, with or without prior pre-treatment with antagonists or inhibitors. Protein expression was assessed by immunohistochemistry, immunofluorescence, ELISA, immunoblot, or Sircoll assays. Transcript expression levels were determined by qRT-PCR. Intact cells were counted using WST assays. RESULTS: IL-4Rα, IL-13Rα1, and collagen are concurrently up-regulated in human peri-urethral prostate tissues from men with LUTS. IL-4 and IL-13 induce their own expression as well as that of their cognate receptors, IL-4Rα and IL-13Rα1. Low concentrations of IL-4 or IL-13 act as cytokines to promote prostate fibroblast proliferation, but higher (>40ng/ml) concentrations repress cellular proliferation. Both IL-4 and IL-13 robustly and specifically promote collagen transcript and protein expression by prostate stromal fibroblasts in a JAK/STAT-dependent manner. Moreover, IL-4 and IL-13-mediated JAK/STAT signaling is coupled to activation of the IL-4Rα receptor. CONCLUSIONS: Taken together, these studies show that IL-4 and IL-13 signal through the IL-4Rα receptor to activate JAK/STAT signaling, thereby promoting their own expression, that of their cognate receptors, and collagens. These finding suggest that the IL-4/IL-13 signaling axis is a powerful, but therapeutically targetable, pro-fibrotic mechanism in the lower urinary tract.