Activated JAK‐STAT Pathway by IL‐6 Mediates Macrophage‐induced Angiotensinogen Augmentation in Renal Proximal Tubular Cells

Abstract

The development of angiotensin II (Ang II)‐dependent hypertension involves increased infiltration of macrophages (MΦ) into the kidney and consequent elevation of intrarenal cytokines including interleukin 6 (IL‐6). The activated JAK‐STAT pathway has been shown to contribute to angiotensinogen (AGT) stimulation in cultured renal proximal tubular cells (PTC). Therefore, this study was performed to demonstrate that activation of JAK‐STAT pathway by IL‐6 derived from Ang II‐treated MΦ mediates AGT upregulation in PTC. Rat MΦ were treated with 0‐10‐5 M Ang II up to 48 hr. Pro‐inflammatory cytokine levels in the culture medium were determined by a multiple cytokine ELISA. IL‐6 mRNA levels were also determined by RT‐PCR. Subsequently, PTC were incubated with the collected medium from the MΦ. After the treatments, STAT3 activity and AGT expression levels in the PTC were evaluated. IL‐6 mRNA and protein expression levels were increased in Ang II‐treated MΦ (1.86 ± 0.14, protein, ratio to control). Moreover, IL‐6 levels were higher than TNF‐α and IL‐1β in the culture medium of Ang II‐treated MΦ. Elevated levels of phosphorylated STAT3 (1.78 ± 0.09, ratio to control), STAT3 nuclear trafficking, and AGT augmentation (1.69 ± 0.04, ratio to control) were observed in PTC receiving the culture medium of Ang II‐treated MΦ. Addition of a neutralizing IL‐6 antibody to the collected medium attenuated the phosphorylation of STAT3 and AGT augmentation in PTC. Additionally, AG490, a JAK2 inhibitor, also suppressed the phosphorylation of STAT3 and AGT augmentation in PTC. These results establish an important role of JAK‐STAT signaling in MΦ‐IL‐6 mediated AGT induction in the kidneys.