The progression of the tubulointerstitial fibrosis driven by stress-induced “proliferation–death” vicious circle

Several hypotheses have been developed to interpret the progression of tubulointerstitial fibrosis (TF), including senescence, epithelial–mesenchymal transition, inflammation, chronic hypoxia, and reactive oxygen species. All of these hypotheses are based on persistent cell injury and localized cell death. Proliferation of neighboring renal tubular epithelial cells (RTECs) is beneficial for organ function recovery from acute injury. However, compensatory proliferation is not always advantageous, as the proliferating cells are vulnerable to ongoing detrimental stimuli, such as inflammation, endocrine stress, high blood pressure, hypoxia/ischemia, and the like. Cell injury and death promotes secretion of growth factors, which evokes proliferation of RTECs; entering the cell cycle makes the RTECs more vulnerable to injury and death. Under persistent stress, death and proliferation are mutually promoted and form the vicious circle that triggers, maintains, and augments the inflammation and progression of TF. We hypothesize that the “proliferation–death” circle is another important pathophysiologic mechanism of TF onset. Through this hypothesis, this paper interprets the development and progression of TF. Moreover, the vicious circle may be universal, underlying the development of inflammation and fibrosis in various organs and tissues. The hypothesis also suggests a potential therapy strategy for the inhibition of fibrosis.     

Elevated K-ras activity with cholestyramine and lovastatin,but not konjac mannan or niacin in lung—–Importance of mouse strain

Our previous work established that hypocholesterolemic agents altered K-ras intracellular localization in lung. Here, we examined K-ras activity to define further its potential importance in lung carcinogenesis. K-ras activity in lungs from male A/J, Swiss and C57BL/6 mice was examined. For 3 weeks, mice consumed either 2 or 4% cholestyramine (CS), 1% niacin, 5% konjac mannan (KM), or were injected with lovastatin 25 mg/kg three or five times weekly (Lov-3X and Lov-5X). A pair-fed (PF) group was fed the same quantity of diet consumed by the Lov-5X mice to control for lower body weights in Lov-5X mice. After 3 weeks, serum cholesterol was assayed with a commercial kit. Activated K-ras protein from lung was affinity precipitated with a Raf-1 ras binding domain-glutathione-S-transferase fusion protein bound to glutathione-agarose beads, followed by Western blotting, K-ras antibody treatment, and chemiluminescent detection. Only KM reduced serum cholesterol (in two of three mouse strains). In C56BL/6 mice treated with Lov-3X, lung K-ras activity increased 1.8-fold versus control (p = 0.009). In normal lung with wild-type K-ras, this would be expected to be associated with maintenance of differentiation. In A/J mice fed 4% CS, K-ras activity increased 2.1-fold (p = 0.02), which might be responsible for the reported enhancement of carcinogenesis in carcinogen-treated rats fed CS. KM feeding and PF treatment had no significant effects on K-ras activity. These data are consistent with the concept that K-ras in lung has an oncogenic function when mutated, but may act as a tumor suppressor when wild-type.