Buffering roles of (pro)renin receptor in starvation-induced autophagy of skeletal muscles

ATP6AP2 knockdown in cardiomyocyte deteriorates heart function via compromising autophagic flux and NLRP3 inflammasome activation

Moderate autophagy can remove damaged proteins and organelles. In some inflammatory diseases, autophagy plays a protective role by inhibiting the NOD-like receptor family pyrin domain containing 3(NLRP3). (Pro)renin receptor (PRR, or ATP6AP2) is a critical component of the V-ATPase required for autophagy. It remains controversial about ATP6AP2 in the pathological process. The impact of ATP6AP2 on NLRP3 inflammasome and autophagic flux remains unknown under pressure overload stress. This research explores the potential link between ATP6AP2, autophagic flux, and NLRP3. There was upregulation of ATP6AP2 from 5-day post-TAC, and this expression remained at a high level until 8-weeks post-TAC in wild mice. Meanwhile, autophagic flux switched from early compensatory activation to blocking in the heart failure phase. NLRP3 activation can be seen at 8-week post-TAC. Adenovirus-mediated knockdown of ATP6AP2(shR-ATP6AP2) accelerated the progress of heart failure. After TAC was induced, shR-ATP6AP2 significantly deteriorated heart function and fibrosis compared with the shR-Scr group. Meanwhile, there was an elevated expression of NLRP3 and autophagic flux blockage. A transgenic mouse(Tg) with cardio-restricted ATP6AP2/(P)RR overexpression was constructed. Although high expression in cardiac tissue, there were no spontaneous functional abnormalities under the basal state. Cardiac function, fibrosis, hypertrophy remained identical to the control TAC group. However, SQSTM1/P62 was reduced, which indicated the relief of autophagic flux blockage. Further, Neonatal rat ventricular myocyte (NRVMs) transfected with shR-ATP6AP2 showed more susceptibility than sh-Scr NRVMs to phenylephrine-induced cell death. More reactive oxygen species (ROS) or mito-ROS accumulated in the shR-ATP6AP2 group when phenylephrine stimulation. Blocking NLRP3 activation in vivo partly rescued cardiac dysfunction and fibrosis. In conclusion, ATP6AP2 upregulation is a compensatory response to pressure overload. If not effectively compensated, it compromises autophagic flux, leads to dysfunctional mitochondria accumulation, further produces ROS to activate NLRP3, eventually accelerates heart failure.

(Pro)renin receptor/ATP6AP2 is required for autophagy and regulates proliferation in lung adenocarcinoma cells

(Pro)renin receptor ((P)RR)/ ATP6AP2 (ATPase, H⁺ transporting, lysosomal accessory protein 2) functions as an essential accessory subunit of vacuolar H⁺ -ATPase (V-ATPase). V-ATPase is necessary for lysosome function and autophagy. Autophagy is related to cell proliferation, migration and invasion of various cancer cells. In this study, we aim to clarify the relationship between (P)RR and autophagy in lung adenocarcinoma. Expression of (P)RR and Ki-67 (a proliferation marker) was studied in sixty-four adenocarcinoma cases by immunohistochemistry. Lung adenocarcinoma cell line, A549, was transfected with (P)RR-specific siRNA. Autophagy inhibitors, bafilomycin A1 and chloroquine, were used as positive controls. Cell proliferation and migration were measured by WST-8 assay and wound healing assay. Autophagosome markers, p62 and LC3, were analyzed by RT-qPCR, Western blot and immunocytochemistry. Immunohistochemistry showed that (P)RR was expressed in all adenocarcinoma tissues. The intensity of (P)RR immunoreactivity was significantly associated with Ki-67. Treatment of (P)RR-specific siRNA suppressed (P)RR expression and significantly reduced cell proliferation and migration as did the autophagy inhibitors. Western blot and immunocytochemistry showed that (P)RR-specific siRNA, as well as the autophagy inhibitors, induced p62 and LC3 accumulation in cytoplasmic granules. These results suggest that (P)RR is involved in cell proliferation and progression of lung adenocarcinoma via regulating autophagy.

The (pro)renin receptor in health and disease

The (pro)renin receptor ((P)RR) was first identified as a single-transmembrane receptor in human kidneys and initially attracted attention owing to its potential role as a regulator of the tissue renin-angiotensin system (RAS). Subsequent studies found that the (P)RR is widely distributed in organs throughout the body, including the kidneys, heart, brain, eyes, placenta and the immune system, and has multifaceted functions in vivo. The (P)RR has roles in various physiological processes, such as the cell cycle, autophagy, acid-base balance, energy metabolism, embryonic development, T cell homeostasis, water balance, blood pressure regulation, cardiac remodelling and maintenance of podocyte structure. These roles of the (P)RR are mediated by its effects on important biological systems and pathways including the tissue RAS, vacuolar H⁺-ATPase, Wnt, partitioning defective homologue (Par) and tyrosine phosphorylation. In addition, the (P)RR has been reported to contribute to the pathogenesis of diseases such as fibrosis, hypertension, pre-eclampsia, diabetic microangiopathy, acute kidney injury, cardiovascular disease, cancer and obesity. Current evidence suggests that the (P)RR has key roles in the normal development and maintenance of vital organs and that dysfunction of the (P)RR is associated with diseases that are characterized by a disruption of the homeostasis of physiological functions.

Pro-renin receptor suppresses mitochondrial biogenesis and function via AMPK/SIRT-1/ PGC-1α pathway in diabetic kidney

Abnormal mitochondrial biogenesis and function has been linked to multiple diseases including diabetes. Recently, we demonstrated the role of renal (Pro)renin receptor (PRR) in the dysregulation of mitochondria. We hypothesized that PRR contributes to the reduction of mitochondrial biogenesis and function in diabetic kidney via PGC-1α/AMPK/SIRT-1 signaling pathway. In vivo and in vitro studies were conducted in C57BL/6 mouse and mouse renal mesangial cells (mRMCs). Control and streptozotocin-induced diabetic mice were injected with scramble or PRR shRNA and followed for a period of eight weeks. PRR mRNA and protein expression increased by 44% and 39% respectively (P<0.05) in kidneys of diabetic mice, and in mRMCs exposed to high glucose by 43 and 61% respectively compared to their respective controls. These results were accompanied by reduced mRNA and protein expressions of PGC-1α (67% and 75%), nuclear respiratory factors (NRF-1, 48% and 53%), mitochondrial transcriptional factor A (mtTFA, 56% and 40%), mitochondrial DNA copy number by 75% (all, P<0.05), and ATP production by 54%, respectively in diabetic kidneys and in mRMCs exposed to high glucose. Compared to non-diabetic control mice, PRR knockdown in diabetic mice and in mRMCs, not only attenuated the PRR mRNA and protein expression but also normalized mRNA and protein expressions of PGC-1α, NRF-1, mtTFA, mitochondrial DNA copy number, and ATP production. Treatment with AMPK inhibitor, Compound C, or SIRT-1 inhibitor, EX-527, alone, or combined with PRR siRNA caused marked reduction of mRNA expression of PGC-1α, NRF-1 and mtTFA, and ATP production in mRMCs exposed to high glucose. In conclusion, our study demonstrated the contribution of the PRR to the reduction of mitochondrial biogenesis and function in diabetic kidney disease via decreasing AMPK/SIRT-1/ PGC-1α signaling pathway.