Liver Sinusoidal Endothelial Cells Suppress Bone Morphogenetic Protein 2 Production in Response to TGFβ Pathway Activation

Abstract

Background & Aims:TGFβ/BMP signalling in the liver plays a critical role in liver disease. Growth factors, such as BMP2, BMP6 and TGFβ1, are released from liver sinusoidal endothelial cells (LSECs) and signal in a paracrine manner to hepatocytes and hepatic stellate cells to control systemic iron homeostasis and fibrotic processes, respectively. The misregulation of the TGFβ/BMP pathway affects expression of the iron-regulated hormone hepcidin causing frequent iron overload and deficiency diseases. However, whether LSEC-secreted factors can act in an autocrine manner to maintain liver homeostasis was not addressed so far.

Bone morphogenetic protein 6–mediated crosstalk between endothelial cells and hepatocytes recapitulates the iron-sensing pathway in vitro

“…In addition, using induced pluripotent stem cell–derived brain ECs as a human blood–brain barrier model, these ECs were shown to engage in iron transport and serve as a critical regulator on the human blood–brain barrier ( 32 ). As for LSECs, it was stated that only in murine LSEC–hepatocytes coculture but not in hepatocyte monoculture, the induction of hepcidin by an ALK5 inhibitor can be observed ( 14 ). Recently, Nrf2 has been suggested as a potential key molecule in mediating iron sensing and controlling BMP6 in LSECs ( 38 ).…”

“…The latter interacts with SMAD4 to form the SMAD complex and then translocates into the nucleus and binds to the hepcidin promoter ( 12 ). Inhibitor of DNA binding 1 (Id1), protein atonal homolog 8, and inhibitory Smad6 and Smad7 are other important modulators of the BMP–SMAD pathway ( 13 , 14 ). In addition, typical mediators of inflammation ( e.g.…”

Iron-dependent BMP6 Regulation in Liver Sinusoidal Endothelial Cells Is Instructed by Hepatocyte-derived Secretory Signals

“…We first explored the requirement of iron accumulation in LSECs for increased Bmp6 messenger RNA (mRNA) expression in vivo by comparing wild‐type (wt) mice maintained on a “high iron” diet’ (Fe high diet) 14 and Fpn(C326S) mice exerting iron overload due to a point mutation in Fpn that disrupts hepcidin binding 15 (http://links.lww.com/HS/A302). From these mice, we isolated HCs and LSECs and analyzed ferritin L protein and transferrin receptor ( Tfr ) 1 mRNA levels, as markers of intracellular iron content.…”

“…As previously shown, this cell preparation is highly pure and maintains fenestrae, denoting lack of cell trans-differentiation. 14 Exposure of LSECs to iron nitrilotriacetate (FeNTA) decreases Tfr1 mRNA expression and activates hemoxygenase1 ( Ho1 ) transcription (Figure 1G, H), indicating that intracellular iron accumulation induces oxidative stress (Figure 1G). By contrast, Bmp6 transcription was not induced (Figure 1I).…”

Repression of the iron exporter ferroportin may contribute to hepatocyte iron overload in individuals with type 2 diabetes

“…Hepa 1–6 cells were cultured in Dulbecco's Modified Eagle's Medium (DMEM) with high glucose (Invitrogen) supplemented with 100 U/ml penicillin and 100 μg/ml streptomycin (Sigma–Aldrich), 10% (v/v) FBS (Gibco). Primary hepatocytes were isolated from C57BL/6 J mice (9 weeks old, males) following a previously described protocol [ 38 ]. Primary hepatocytes were plated in a density of 5 × 10 4 cells/cm 2 and cultured in William's E medium (Life Technologies) supplemented with 4% (v/v) FBS, 100 U/ml penicillin and 100 μg/ml streptomycin.…”