Rapamycin attenuates liver graft injury in cirrhotic recipient--the significance of down-regulation of Rho-ROCK-VEGF pathway

The roles of lipocalin-2 in small-for-size fatty liver graft injury

OBJECTIVE

To investigate the roles and underlying mechanism of an inflammatory mediator-lipocalin-2 (Lcn2) in small-for-size fatty graft liver injury.

BACKGROUND

Understanding of the distinct mechanism regulating small-for-size fatty liver graft injury will be crucial to prevent marginal graft failure during living donor liver transplantation (LDLT).

METHODS

The roles of Lcn2 in small fatty graft injury were investigated in orthotopic liver transplantation model rats, human LDLT samples, an in vitro simulated ischemia-reperfusion (IR) model, and a hepatic ischemic reperfusion plus major hepatectomy (IR + H) model in mice.

RESULTS

Our result showed that Lcn2 was significantly upregulated together with elevation of chemokine (C-X-C motif) ligand 10 (CXCL10) and activation/infiltration of intragraft macrophages after liver transplantation using small-for-size fatty liver graft compared with that of using small-for-size normal liver graft. Intragraft and plasma levels of Lcn2 were intensified in patients who underwent transplantation with small-for-size fatty graft after LDLT. Lcn2 and CXCL10 were expressed higher in fatty hepatocytes after the simulated IR injury compared with normal hepatocytes. Overexpression of Lcn2 significantly deteriorated IR + H-induced hepatic injury in correlation with upregulation of CXCL10 and augmentation of infiltrated macrophages. On the contrary, hepatic injury of small fatty liver remnant after IR + H operation was attenuated in the Lcn-2 mice because of suppression of CXCL10 expression and diminishment of macrophage infiltration.

CONCLUSIONS

Lcn2 is an important regulator in small-for-size fatty liver graft injury and targeting Lcn2 may be feasible for preventing marginal graft failure in LDLT.

RhoA and Rho kinase mediate cyclosporine A and sirolimus-induced barrier tightening in renal proximal tubular cells

The regulation and maintenance of the paracellular transport in renal tubular epithelia is vital for kidney functions. Combination of the immunosuppressant drugs cyclosporine A (CsA) and sirolimus (SRL) exerts powerful immunosuppression, but also causes nephrotoxicity. We have previously shown that CsA and SRL elevate transepithelial resistance (TER) in kidney tubular cells partly through MEK/ERK1/2. In this work we examined the hypothesis that the RhoA pathway may also be mediating effects of CsA and SRL. We show that CsA and the CsA/SRL combination activated RhoA, induced cofilin phosphorylation and promoted stress fiber generation. The Rho kinase (ROK) inhibitor, Y27632, prevented CsA and CsA/SRL-induced cofilin phosphorylation and actin remodelling, reduced the TER increase and prevented the rise in claudin-7 levels caused by the drugs. Expression of the exchange factor GEF-H1/lfc was elevated in cells treated with CsA and CsA/SRL. GEF-H1 silencing inhibited RhoA activation by ≈50%, and potently reduced cofilin phosphorylation and stress fiber formation induced by CsA and CsA/SRL. However, GEF-H1 downregulation did not prevent the TER change. Thus the Rho/Rho kinase pathway was involved in mediating CsA and CsA/SRL-induced cytoskeleton rearrangement and TER changes via claudin-7 expression. Our data however point to differential regulation of Rho activation involved in central cytoskeleton remodelling, that is GEF-H1-dependent and junctional permeability that does not require GEF-H1.

The impact of sirolimus on hepatocyte proliferation after living donor liver transplantation

BACKGROUND

There is a lack of data on the use of sirolimus after partial liver transplantation, especially regarding its impact on post-transplant regeneration.

METHODS

We reviewed adult living donor transplantations, with de novo sirolimus (n = 7) and without sirolimus (n = 21). Liver biopsies were stained for KI-67, a proliferation marker. Controls included specimens with normal liver parenchyma (n = 13).

RESULTS

Both groups had similar demographics, graft and patient survival and complication rates. During the first six wk and over the whole first year post-transplant, the use of sirolimus was associated with lower levels of hepatocyte proliferation compared to sirolimus-free patients, (overall, 0.3 [0-7.2] vs. 3 [0-49] KI-67 positive hepatocytes per high power field, p ≤ 0.05). The levels observed in the sirolimus group were similar to those seen in non-transplanted control patients with normal parenchyma (0.2 [0-1.3], p = NS). Post-transplant hepatocyte proliferation correlated with the serum levels of sirolimus (p ≤ 0.05), but not with those of tacrolimus or with the dose of mycophenolate mofetil (p = 0.9 and 0.3, respectively).

CONCLUSIONS

These data suggest that sirolimus is associated with decreased post-transplant hepatocyte proliferation. The clinical significance of this observation remains to be fully determined.

Sirolimus attenuates reduced-size liver ischemia-reperfusion injury but impairs liver regeneration in rats

BACKGROUND

Evidence has suggested that immunosuppressive drugs impact ischemia-reperfusion injury.

AIMS

The purpose of the present study was to evaluate the effect of sirolimus on hepatic injury and regeneration in a rat reduced-size liver ischemia-reperfusion model.

METHODS

Using a newly developed rat reduced-size liver ischemia-reperfusion injury model, the effects of sirolimus were evaluated by assessing liver cell apoptosis and aspartate aminotransferase, myeloperoxidase, and malondialdehyde levels. In addition, liver regeneration after sirolimus treatment was evaluated by measuring liver weight resumption and by the histological examination of bromodeoxyuridine and proliferating cell nuclear antigen expression.

RESULTS

Sirolimus significantly decreased liver cell apoptosis as well as tissue myeloperoxidase and malondialdehyde levels, but impaired postischemic liver regeneration. Ischemia-reperfusion-induced elevation of aspartate aminotransferase serum levels was significantly decreased by sirolimus.

CONCLUSIONS

Despite an impairment of postischemic liver proliferation, sirolimus demonstrated beneficial amelioration of ischemia-reperfusion-induced liver injury in a reduced-size liver model in rats.

Distinct mechanism of small-for-size fatty liver graft injury--Wnt4 signaling activates hepatic stellate cells

In this study, we aimed to investigate the significance of hepatic stellate cells (HSCs) activation in small-for-size fatty liver graft injury and to explore the underlying molecular mechanism in a rat liver transplantation model. A rat orthotopic liver transplantation model using fatty grafts (40% of fatty changes) and cirrhotic recipients was applied. Intragraft gene expression profiles, ultrastructure features and HSCs activation were compared among the rats received different types of grafts (whole vs. small-for-size, normal vs. fatty). The distinct molecular signature of small-for-size fatty graft injury was identified by cDNA microarray screening and confirmed by RT-PCR detection. In vitro functional studies were further conducted to investigate the direct effect of specific molecular signature on HSCs activation. HSCs activation was predominantly present in small-for-size fatty grafts during the first 2 weeks after transplantation, and was strongly correlated with progressive hepatic sinusoidal damage and significant upregulation of intragraft Wnt4 signaling pathway. In vitro suppression of Wnt4 expression could inhibit HSC activation directly. In conclusion, upregulation of Wnt4 signaling led to direct HSC activation and subsequently induced small-for-size fatty liver grafts injury. Discovery of this distinct mechanism may lay the foundation for prophylactic treatment for marginal graft injury in living donor liver transplantation.

Suppression of liver tumor growth and metastasis by adiponectin in nude mice through inhibition of tumor angiogenesis and downregulation of Rho kinase/IFN-inducible protein 10/matrix metalloproteinase 9 signaling

PURPOSE

We aimed to investigate the effects of adiponectin on liver cancer growth and metastasis and explore the underlying mechanisms.

EXPERIMENTAL DESIGN

An orthotopic liver tumor nude mice model with distant metastatic potential was applied. Either Ad-adiponectin (1 x 10(8); treatment group) or Ad-luciferase (control group) was injected via portal vein after tumor implantation. Tumor growth and metastasis were monitored by Xenogen In vivo Imaging System. Hepatic stellate cell activation by alpha-smooth muscle actin staining, microvessel density by CD34 staining, macrophage infiltration in tumor tissue, and cell signaling leading to invasion, migration [Rho kinase (ROCK), IFN-inducible protein 10 (IP10), and matrix metalloproteinase 9], and angiogenesis [vascular endothelial growth factor (VEGF) and angiopoietin 1] were also compared. Tumor-nontumor margin was examined under electron microscopy. Direct effects of adiponectin on liver cancer cells and endothelial cells were further investigated by a series of functional studies.

RESULTS

Tumor growth was significantly inhibited by adiponectin treatment, accompanied by a lower incidence of lung metastasis. Hepatic stellate cell activation and macrophage infiltration in the liver tumors were suppressed by adiponectin treatment, along with decreased microvessel density. The treatment group had less Ki-67-positive tumor cells and downregulated protein expression of ROCK1, proline-rich tyrosine kinase 2, and VEGF. Tumor vascular endothelial cell damage was found in the treatment group under electron microscopy. In vitro functional study showed that adiponectin not only downregulated the ROCK/IP10/VEGF signaling pathway but also inhibited the formation of lamellipodia, which contribute to cell migration.

CONCLUSION

Adiponectin treatment significantly inhibited liver tumor growth and metastasis by suppression of tumor angiogenesis and downregulation of the ROCK/IP10/matrix metalloproteinase 9 pathway.

Sirolimus-induced signaling modifications in Kaposi's sarcoma with resolution in a liver transplant recipient

Sirolimus is one treatment option in transplant recipients with Kaposi's sarcoma (KS), which involves dysregulation of Akt-mammalian target of rapamycin (mTOR) signaling pathway. Signal modifications after sirolimus therapy in organ recipients with KS are largely unknown and not verified. We reported a case of KS found two yr after liver transplantation in which the immunosuppression was changed from tacrolimus, MMF, and steroid to sirolimus alone. In skin, which was found to have persistent KS after a two-month treatment of sirolimus and was removed completely one yr later, KS was no longer present. The patient went well without graft rejection. Tumor biopsies were performed before, two months, and one yr after the start of sirolimus. Immunohistochemical staining of vascular endothelial growth factor (VEGF), p-Akt, p-mTOR, p-p70 S6 kinase, and Western blot for p-tuberin/ tuberous sclerosis complex (TSC)2 was performed. VEGF was suppressed thoroughly in two-month use of sirolimus. In addition, p-Akt and p-mTOR, which were decreased at two months, could not be detected after one yr of treatment. Moreover, p-p70 S6 kinase, expressed strongly in overlying epidermis initially, was suppressed completely after two months of treatment. However, p-tuberin/TSC2, contrary to suggested theoretically, was not detected through all specimens, implying not to be a significant event. Suppressed expression of VEGF, p-Akt, and p-mTOR was the major event of signaling modification through the long-term use of sirolimus.

Sp-1 and c-Myc mediate lysophosphatidic acid-induced expression of vascular endothelial growth factor in ovarian cancer cells via a hypoxia-inducible factor-1-independent mechanism

PURPOSE

Lysophosphatidic acid (LPA), which is present in ascites of ovarian cancer patients, stimulates expression of vascular endothelial growth factor (VEGF). VEGF is essential for the development and abdominal dissemination of ovarian cancer. We examined how LPA drives VEGF expression to gain a better understanding of tumor angiogenesis under normoxic conditions.

EXPERIMENTAL DESIGN

ELISA, Northern blotting, immunoblotting, quantitative PCR, and promoter reporter analysis in combination with small interfering RNA and pharmacologic inhibitors were used to examine LPA-induced VEGF expression and the underlying mechanisms.

RESULTS

LPA stimulated expression of multiple VEGF variants. A 123-bp fragment proximal to the transcriptional initiation site was identified to be functional promoter region responsible for the response to LPA. The fragment harbors consensus sites for several transcription factors including c-Myc and Sp-1 but not hypoxia-inducible factor-1. Blockade of Rho, ROCK, or c-Myc reduced LPA-dependent VEGF production and promoter activation, suggesting that the G12/13-Rho-ROCK-c-Myc cascade partially contributes to VEGF induction by LPA. More significantly, the multiple Sp-1 sites within the responsive region of the VEGF promoter were essential for LPA-mediated transcription. LPA induced Sp-1 phosphorylation and DNA-binding and transcriptional activities. The silencing of Sp-1 expression with small interfering RNA or inhibition of Sp-1 with pharmacologic inhibitors blocked VEGF production induced by LPA.

CONCLUSIONS

LPA stimulates hypoxia-inducible factor-1-independent VEGF expression to promote tumor angiogenesis through activation of the c-Myc and Sp-1 transcription factors.

Impact of rapamycin on liver regeneration

The remarkable capacity of the liver to regenerate after injury and the prospects of organ self-renewal have attracted much interest in the understanding and modulation of the underlying molecular events. We investigated the effect of mammalian target of rapamycin (mTOR) inhibitor rapamycin (RAPA) on liver by correlating intravital microscopy, immunohistochemistry, and reverse transcriptase polymerase chain reaction in a rat model of 2/3 hepatectomy. RAPA significantly retarded proliferation of hepatocytes, endothelial cells, and hepatic stellate cells (HSCs) mostly between days 2 and 4 after hepatectomy and downregulated major cytokines and growth factors (tumor necrosis factor alpha, hepatocyte growth factor, platelet-derived growth factor, platelet-derived growth factor receptor, insulin-like growth factor-1, transforming growth factor beta 1) important for liver regeneration. These effects were almost absent at later time points. RAPA also had a transient, but broad effect on angiogenesis, and impaired sinusoidal density as well as mRNA levels of vascular endothelial growth factor, vascular endothelial growth factor receptor 1, vascular endothelial growth factor receptor 2, and angiopoietin-1. Activation of HSC was also transiently suppressed as observed by smooth muscle protein 1 alpha protein expression and intercellular adhesion molecule-1 mRNA levels. The rate of apoptosis in liver was significantly increased by RAPA between day 3 and day 7. The effect of RAPA on liver repair, angiogenesis, and HSC activation is confined to the phase of active cell proliferation. This transient effect might allow further exploration of mTOR inhibitors in clinical situations that involve liver regeneration, and seems to have implications beyond immunosuppression.

Ischemia-reperfusion of small liver remnant promotes liver tumor growth and metastases--activation of cell invasion and migration pathways

Elucidating the mechanism of liver tumor growth and metastasis after hepatic ischemia-reperfusion (I/R) injury of a small liver remnant will lay the foundation for the development of therapeutic strategies to target small liver remnant injury, and will reduce the likelihood of tumor recurrence after major hepatectomy or liver transplantation for liver cancer patients. In the current study, we aimed to investigate the effect of hepatic I/R injury of a small liver remnant on liver tumor development and metastases, and to explore the precise molecular mechanisms. A rat liver tumor model that underwent partial hepatic I/R injury with or without major hepatectomy was investigated. Liver tumor growth and metastases were compared among the groups with different surgical stress. An orthotopic liver tumor nude mice model was used to further confirm the invasiveness of the tumor cells from the above rat liver tumor model. Significant tumor growth and intrahepatic metastasis (5 of 6 vs. 0 of 6, P=0.015), and lung metastasis (5 of 6 vs. 0 of 6, P=0.015) were found in rats undergoing I/R and major hepatectomy compared with the control group, and was accompanied by upregulation of mRNA levels for Cdc42, ROCK (Rho kinase), and vascular endothelial growth factor, as well as activation of hepatic stellate cells. Most of the nude mice implanted with liver tumor from rats under I/R injury and major hepatectomy developed intrahepatic and lung metastases. In conclusion, hepatic I/R injury of a small liver remnant exacerbated liver tumor growth and metastasis by marked activation of cell adhesion, invasion, and angiogenesis pathways.

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