Effects of tacrolimus and dexamethasone on tubulointerstitial fibrosis in mercuric chloride treated Brown Norway rats

Short-term dexamethasone treatment transiently, but not permanently, attenuates fibrosis after acute-to-chronic kidney injury

Background

Acute kidney injury (AKI) is an underestimated, yet important, risk factor for the development of chronic kidney disease (CKD). Persistence of inflammation after a renal ischemic injury has been observed, both in experimental models and patients, and is thought to be an important mechanisms underlying progression of acute-to-chronic renal injury. Temporary suppression of inflammation immediately after AKI might therefore be a good first-line therapeutic strategy towards a better long term outcome.

Methods

Male C57Bl/6 J mice (Charles River, 10–12 weeks of age) underwent warm (36 °C body temperature) unilateral ischemia-reperfusion of the kidney for 21 min, after which treatment with intraperitoneal injection of the corticosteroid dexamethasone (10 mg/kg) was initiated for 3 weeks. Both at that time point and after an additional 3 week post-treatment follow up period, fibrosis was quantified by collagen I gene expression and immunostaining, as well as gene expression analysis of fibrosis-related genes Tgfβ, Ccn2 (Ctgf), Pai-1 and Ccn3. Furthermore, inflammation was evaluated by Tnfα gene expression and protein expression of the F4/80 macrophage marker and the α-SMA fibroblast marker. Lastly, renal histopathology was quantified by a morphometric analysis of the tubulointerstitial area.

Results

Treatment with dexamethasone attenuated development of fibrosis, as evidenced by reduced collagen I gene expression and immunostaining, in combination with reduced gene expression of the pro-fibrotic Ccn2 and increased expression of the anti-fibrotic Ccn3. The effects of dexamethasone on renal fibrosis persisted during the 3 week follow up period, as evidenced by stagnation of collagen I deposition in the ischemic kidney, in contrast to vehicle-treatment, where progression of fibrosis was observed. However, expression levels of the pro-fibrotic genes re-approached those of vehicle-treated injured kidneys suggesting that the effects of dexamethasone on fibrosis beyond the treatment period are temporary.

Conclusion

A short term anti-inflammatory therapy with dexamethasone only transiently attenuates ischemia induced fibrosis. Prolonged or persistent anti-inflammatory treatment seems warranted to achieve long term benefit.

Electronic supplementary material

The online version of this article (10.1186/s12882-018-1151-7) contains supplementary material, which is available to authorized users.

Losartan and Dexamethasone may inhibit chemotaxis to reduce the infiltration of Th22 cells in IgA nephropathy

Angiotensin II is considered a major profibrotic factor that is involved in tissue remodeling processes, as the inhibition of Angiotensin II can halt renal inflammatory processes. Dexamethasone, an important anti-inflammatory and immunosuppressive agent, has been widely used to treat renal disease for decades. In this study, we explored the frequency of Th22 cells in a mouse model of IgA nephropathy and compared the possible effects of Losartan and Dexamethasone on Th22 cells. The experiments were performed using 6-week-old BALB/c female mice in an established IgA nephropathy model. The mice were randomly separated into 4 groups, which were administered Losartan (30mg/kg/d) or Dexamethasone (10mg/kg/d) and subjected to IgA nephropathy or the normal control treatment for 1month. The frequency of Th22 cells was measured via flow cytometry, and the relative pathological changes in renal morphology were measured with different pathological staining methods. Immunohistochemistry was performed to verify the expression of CCR10 and CCL27, which is specialized receptor on Th22 cells and its corresponding chemokine, respectively. The concentrations of CCL27 and IL-22 in renal tissue homogenates and sera were detected using ELISAs. Losartan and Dexamethasone differentially decreased the frequency of Th22 cells after 1month, and mesangial cell proliferation was also improved. Moreover, the expression of CCR10, CCL27 and IL-22 was reduced by treatment with either drug. However, significant differences between Losartan and Dexamethasone were not observed. Based on these findings, Losartan and Dexamethasone may suppress inflammatory responses by inhibiting the chemotaxis of Th22 cells in IgA nephropathy.

Inhibition of cardiac myofibroblast formation and collagen synthesis by activation and overexpression of adenylyl cyclase

Transformation of fibroblasts to myofibroblasts, characterized by expression of alpha-smooth muscle actin (alpha-SMA) and production of extracellular matrix (ECM) components, is a key event in connective tissue remodeling. Approaches to inhibit this transformation are needed in tissues, such as the heart, where excessive ECM production by cardiac fibroblasts (CFs) causes fibrosis, myocardial stiffening, and cardiac dysfunction. We tested whether adenylyl cyclase (AC) activation (increased cAMP levels) modulates the transformation of adult rat CF to myofibroblasts, as assessed by immunofluorescent microscopy, immunoblotting, and collagen synthesis. A 24-h incubation of CF with TGF-beta or angiotensin II increased alpha-SMA expression, which was inhibited by the AC agonist forskolin and a cAMP analog that activates protein kinase A. Treatment with forskolin blunted serum-, TGF-beta-, and angiotensin II-stimulated collagen synthesis. CFs engineered to overexpress type 6 AC had enhanced forskolin-promoted cAMP formation, greater inhibition by forskolin of TGF-beta-stimulated alpha-SMA expression, and a decrease in the EC(50) of forskolin to reduce serum-stimulated collagen synthesis. The AC stimulatory agonist adrenomedullin inhibited collagen synthesis in CF that overexpressed AC6 but not in controls. Thus, AC stimulation blunts collagen synthesis and, in parallel, the transformation of adult rat CF to myofibroblasts. AC overexpression enhances these effects, "uncovering" an inhibition by adrenomedullin. These findings implicate cAMP as an inhibitor of ECM formation by means of blockade of the transformation of CF to myofibroblasts and suggest that increasing AC expression, thereby enhancing cAMP generation through stimulation of receptors expressed on CF, could provide a means to attenuate and prevent cardiac fibrosis and its sequelae.