Previous studies have shown that acute kidney injury (AKI) is exacerbated in C-reactive protein transgenic mice (CRP Tg) and alleviated in Smad3 knockout mice (Smad3 KO). The present study used CRP Tg, Smad3 KO, and CRP Tg/Smad3 KO mice to investigate the signaling mechanisms by which CRP promotes AKI. As previously reported, we found that the elevation of serum creatinine and the extent of tubular epithelial cell (TEC) necrosis following ischemia-reperfusion injury (IRI) induced AKI was greater for CRP Tg than wild type (Wt). In contrast in Smad3 KO mice, whether CRP Wt or CRP Tg, these responses were blunted. Exacerbation of AKI in CRP Tg was associated with increased TGF-β/Smad3 signaling, i.e. increased expression of the cyclin kinase inhibitor p27, suppression of phosphorylated CDK2, and decreased expression of cyclin E. Concomitantly, TEC proliferation was arrested at the G1 phase in CRP Tg, as evidenced by fewer BrdU+ and PCNA+ cells. On the other hand protection from AKI in Smad3 KO mice was associated with decreased expression of p27 and promotion of CDK2/cyclin E-dependent G1/S transition of TECs. In vitro studies using human TEC showed that (i) CRP activates Smad3 via both TGF-β-dependent and ERK/MAPK crosstalk mechanisms, (ii) Smad3 binds directly to p27, and (iii) blockade of Smad3 or the Fc receptor CD32 prevents CRP-induced p27-dependent G1 cell cycle arrest. In vivo, treatment of CRP Tg with a Smad3 inhibitor improved AKI outcomes. In their sum these data suggest that in CRP Tg mice undergoing AKI, impaired TEC regeneration is likely the result of CD32-Smad3-p27 driven inhibition of the CDK2/cyclin E complex. Targeting Smad3 may offer a new treatment approach for AKI.

Silybin is a secondary metabolite isolated from the seeds of blessed milk thistle (Silybum marianum) that has anti-inflammatory, antioxidative, antifibrotic, and antitumor properties. Here, we showed that silybin protected against cisplatin-induced acute kidney injury (AKI) by improving mitochondrial function through the regulation of sirtuin 3 (SIRT3) expression. Male SV129 and SIRT3 knockout (KO) mice were administered a single intraperitoneal (i.p.) injection of cisplatin with or without treatment with silybin. Moreover, cultured HK2 cells were used to evaluate mitochondrial morphology and function. Our data suggested that silybin enhanced SIRT3 expression after cisplatin administration both in vivo and in vitro. Silybin treatment improved mitochondrial function and bioenergetics in wild-type, but not SIRT3-defective, cells and mice. Moreover, we demonstrated that silybin markedly attenuated cisplatin-induced AKI and tubular cell apoptosis and improved cell regeneration in a SIRT3-dependent manner. Collectively, these results suggest that silybin is a pharmacological activator of SIRT3 capable of protecting against cisplatin-induced tubular cell apoptosis and AKI by improving mitochondrial function. Thus, silybin could serve as a potential clinical renoprotective adjuvant treatment in cisplatin chemotherapy.

Acute kidney injury (AKI), which is an important cause of secondary chronic kidney disease (CKD) and death in hospitalized patients, has become a worldwide public health concern. Approximately 13 million people suffer from AKI every year, and approximately 1.7 million people die from AKI and its complications. 1,2 The aetiology of AKI is diverse, including severe infections, heart disease, haematological tumours and nephrotoxic drugs. Cisplatin is one of the most efficient and widely used antineoplastic in the clinic. Theapeutic effects of cisplatin are positively correlated with its dose, but so are its toxicity and side effects. Renal toxicity is one of the most common and severe reactions