Date Published: June 30, 2017
Publisher: John Wiley and Sons Inc.
Author(s): Eun Kyeong Lee, Ki Wung Chung, Ye Ra Kim, Sugyeong Ha, Sung Dae Kim, Dae Hyun Kim, Kyung Jin Jung, Bonggi Lee, Eunok Im, Byung Pal Yu, Hae Young Chung.
We have recently reported that TLR‐related genes, including TLR7, are upregulated during aging. However, the role of TLR7 and its endogenous ligand in inflammation related to aging is not well defined. Here, we established that small RNAs trigger age‐related renal inflammation via TLR7 signaling pathway. We first investigated the expression changes of nine different TLRs in kidney of 6‐month‐old young rats and 20‐month‐old aged rats. The results revealed that the expression of TLR7 was the highest among nine TLRs in kidney of old rats compared to the young aged rats. Next, to assess the role of cellular RNA as a TLR7 ligand, we treated a renal tubular epithelial cell line with total RNA isolated from the kidney of young and old rats. The results showed that RNA isolated from old rats showed higher expression of TLR7, IL1β, and TNFα compared to that from young rats. Furthermore, RNA isolated from old rats induced IKKα/β/JNK/NF‐κB activation. To identify RNA that activates TLR7, we isolated small and large RNAs from old rat kidney and found that small RNAs increased TLR7 expression in cells. Finally, to investigate the local inflammatory response by small RNA, C57B/L6 mice were intraperitoneally injected with small RNAs isolated from young and old rats; thereby, RNA isolated from old rats induced higher inflammatory responses. Our study demonstrates that renal small RNAs from aged rats induce pro‐inflammatory processes via the activation of the TLR7/IKKα/β/JNK/NF‐κB signaling pathway, and highlights its causative role as a possible therapeutic target in age‐related chronic renal inflammation.
Accumulated data strongly suggest that chronic and systemic upregulation of pro‐inflammatory mediators, including C‐reactive protein (CRP), interleukin (IL)‐6, tumor necrosis factor (TNF) α, and cyclooxygenase (COX)‐2, is induced by aging and that consequently, these pro‐inflammatory molecular events contribute to the development of aging and age‐related diseases (Chung et al., 2009, 2011). We have recently examined age‐related differential gene expression within the rat kidney genome using next‐generation sequencing (NGS). The results showed that genes related to kidney inflammation are upregulated during aging, especially Toll‐like receptors (TLRs) and TLR signaling‐related genes. Notably, the TLR7 mRNA expression is the highest among the TLRs family (Park et al., 2016). Feldman et al. (2015) also reported the occurrence of TLR‐related inflammation during aging‐related pathology progression. Thus, these studies imply that TLR activation mediates age‐related inflammation and may contribute to the aging process as well as the development of age‐related disease.
In the current study, we found that small RNAs isolated from old rat kidneys increase the pro‐inflammatory TLR7 activation via the IKKα/β/JNK/NF‐κB pathway during aging. Previously, we reported that TLR signaling‐related molecules are increased in kidney of 25‐month‐old rats based on RNA whole‐genome sequencing analysis (Park et al., 2016). As a follow‐up, in the present study, we further explored the role of TLR7 in renal aging and aimed at determining whether RNA isolated from old rats can function as a novel endogenous ligand of TLR7 and thereby induce its activation in kidney cells. The results revealed that treatment of cultured NRK52E cells with total RNA isolated from old rats induced a significant increase in the expressions of TLR7 and cytokines. Our data revealed that total RNA isolated from old rats increases considerably TLR7 activation compared to that of young rats. And we have also shown that, the increase of TLR7 activation by total RNA isolated from old rats was mediated through IKKα/β/JNK/NF‐κB activation. Moreover, among the total RNA, small RNAs isolated from aged rat kidney increased TLR7 expression, while large RNAs did not. Finally, small RNAs isolated from old rat kidney led to a significant increase in local inflammatory responses after its peritoneal injection into mice when compared to inflammatory responses observed with small RNAs isolated from young rat injected into mice.
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIP) (No. 2009‐0083538). This research was also supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2014R1A1A2008973).This research was supported by Bio & Medical Technology Development Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Plannig (No. 2015M3A9B8029074).
E.K. Lee, D.H. Kim, B. Lee, K. J. Jung, and H.Y. Chung involved in conception and design of study; E.K. Lee, K.W. Chung, R. Kim, S Ha, and S.D. Kim involved in helping with an experiment; E.K. Lee, K.W. Chung, Y. R. Kim, S.D. Kim, D.H. Kim, B. Lee, K.J. Jung, and H.Y. Chung involved in analysis and/or interpretation of data; E.K. Lee, B.P. Yu, and H.Y. Chung involved in drafting the manuscript; E.K. Lee, K.W. Chung, Y. R. Kim, D.H. Kim, B. Lee, K. J. Jung, B.P. Yu, and H.Y. Chung involved in revising the manuscript critically for important intellectual content.
The authors declare that they have no competing interests.