Major histocompatibility complex (MHC) class II molecules acquire antigenic peptides after degradation of the invariant chain (Ii), an MHC class II-associated protein that otherwise blocks peptide binding. Antigen-presenting cells of mice that lack the protease cathepsin S fail to process Ii beyond a 10 kDa fragment, resulting in delayed peptide loading and accumulation of cell surface MHC class II/10 kDa Ii complexes. Although cathepsin S-deficient mice have normal numbers of B and T cells and normal IgE responses, they show markedly impaired antibody class switching to IgG2a and IgG3. These results indicate cathepsin S is a major Ii-processing enzyme in splenocytes and dendritic cells. Its role in humoral immunity critically depends on how antigens access the immune system.

Contrast-induced acute kidney injury (CI-AKI) occurs in more than 30% of patients after intravenous iodinated contrast media and causes serious complications, including renal failure and mortality. Recent research has demonstrated that routine antioxidant and alkaline therapy failed to show benefits in CI-AKI patients with high risk for renal complications. Mitophagy is a mechanism of selective autophagy, which controls mitochondrial quality and mitochondrial reactive oxygen species (ROS) through degradation of damaged mitochondria. The role of mitophagy and its regulation of apoptosis in CI-AKI are poorly understood. In this study, we demonstrated that mitophagy was induced in renal tubular epithelial cells (RTECs) during CI-AKI, both in vivo and in vitro . Meanwhile, contrast media–induced mitophagy was abolished when silencing PINK1 or PARK2 (Parkin), indicating a dominant role of the PINK1-Parkin pathway in mitophagy. Moreover, mitochondrial damage, mitochondrial ROS, RTEC apoptosis, and renal injury under contrast exposure were more severe in PINK1- or PARK2-deficient cells and mice than in wild-type groups. Functionally, PINK1-Parkin–mediated mitophagy prevented RTEC apoptosis and tissue damage in CI-AKI through reducing mitochondrial ROS and subsequent NLRP3 inflammasome activation. These results demonstrated that PINK1-Parkin–mediated mitophagy played a protective role in CI-AKI by reducing NLRP3 inflammasome activation.

Background/Aims: Contrast-induced nephropathy (CIN) is at present the third leading cause of hospital-acquired acute kidney injury (AKI). Traditionally, it is diagnosed by measuring the increase of the serum creatinine concentration. However, in patients with acute changes in their glomerular filtration rate, serum creatinine is an insensitive marker. This clinical study was designed to investigate whether human urinary interleukin-18 (IL-18) and neutrophil gelatinase-associated lipocalin (NGAL) are early predictive markers for AKI after coronary angiography and their correlation with later cardiac events. Methods: Patients undergoing coronary angiography using low-osmolar contrast medium were enrolled and then followed up for at least 17 months. Urine samples were collected before and 24 h after coronary angiography and IL-18 and NGAL levels measured by using an ELISA kit. Results: CIN was diagnosed in 13 of 150 (8.7%) patients (CIN group); 27 patients without CIN served as control group. At 24 h after the procedure, the urinary IL-18 and NGAL levels were significantly increased in the CIN group, but not in the control group (p < 0.05). The predictable time of AKI onset determined by IL-18 was 24 h earlier than determined by serum creatinine (p < 0.01). Receiver operating characteristic curve analysis showed that both IL-18 and NGAL showed a good performance in early diagnosis of CIN as compared with serum creatinine (p < 0.05). We also found that IL-18 is an independent predictive marker for later major cardiac events: relative risk = 2.09 (p < 0.01). Conclusions: We conclude that urinary IL-18 or NGAL could be early biomarkers of CIN and that urinary IL-18 is well associated with the later cardiac outcomes in patients after coronary angiography.

The importance of astrocytic K(+) uptake for extracellular K(+) ([K(+)](e)) clearance during neuronal stimulation or pathophysiological conditions is increasingly acknowledged. It occurs by preferential stimulation of the astrocytic Na(+),K(+)-ATPase, which has higher K(m) and V(max) values than its neuronal counterpart, at more highly increased [K(+)](e) with additional support of the cotransporter NKCC1. Triggered by a recent DiNuzzo et al. paper, we used administration of the glycogenolysis inhibitor DAB to primary cultures of mouse astrocytes to determine whether K(+) uptake required K(+)-stimulated glycogenolysis. KCl was increased by either 5 mM (stimulating only the Na(+),K(+)-ATPase) or 10 mM (stimulating both transporters) in glucose-containing saline media prepared to become iso-osmotic after the addition. DAB completely inhibited both uptakes, the Na(+),K(+)-ATPase-mediated by preventing Na(+) uptake for stimulation of its intracellular Na(+)-activated site, and the NKCC1-mediated uptake by inhibition of depolarization- and L-channel-mediated Ca(2+) uptake. Drugs inhibiting the signaling pathways involved in either of these processes also abolished K(+) uptake. Assuming similar in vivo characteristics, partly supported by literature data, K(+)-stimulated astrocytic K(+) uptake must discontinue after normalization of extracellular K(+). This will allow Kir1.4-mediated release and reuptake by the less powerful neuronal Na(+),K(+)-ATPase.