Depletion of hepatic stellate cells: Have Kupffer cells lost their bad neighbor?
Authors: Ricardo Marcos
Journal: Journal of Hepatology (2014)

A novel mouse model of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injuryJournal of HepatologyVol. 60Issue 2PreviewHepatic stellate cells (HSCs) that express glial fibrillary acidic protein (GFAP) are located between the sinusoidal endothelial cells and hepatocytes. HSCs are activated during liver injury and cause hepatic fibrosis by producing excessive extracellular matrix. HSCs also produce many growth factors, chemokines and cytokines, and thus may play an important role in acute liver injury. However, this function has not been clarified due to unavailability of a model, in which HSCs are depleted from the normal liver. Full-Text PDF Reply to: “Depletion of hepatic stellate cells: Have Kupffer cells lost their bad neighbor?”Journal of HepatologyVol. 61Issue 3PreviewWe appreciate the insightful commentary by Marcos on our recently published manuscript [1], where they suggest that the loss of communication between hepatic stellate cells (HSCs) and closely associated Kupffer cells can be an important mechanism of the amelioration of ischemia/reperfusion (I/R)- or LPS-induced injury in HSC-depleted liver. We agree with this view since Kupffer cells have been shown to elicit inflammatory response, and their blockade or elimination ameliorates hepatic injury in several animal models [2]. Full-Text PDF Open Access In a recent issue of this journal, Stewart et al. [[1]Stewart R.K. Dangi A. Huang C. Murase N. Kimura S. Stolz D.B. et al.A novel method of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injury.J Hepatol. 2014; 60: 298-305Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar] presented a major breakthrough in liver research models. The authors used transgenic mice expressing herpes simplex virus thymidine kinase (TK) under the glial fibrillary acidic protein (GFAP) promoter. Proliferation of hepatic stellate cells (HSC) was first induced by CCl4 and then mice were treated with ganciclovir, which was metabolized by TK into toxic nucleotide analogues, ultimately leading to HSC death (≈70% depletion). Afterwards, mice were subjected to ischemia/reperfusion and to endotoxin treatments. The role of HSC in these acute injuries was studied – so far it has not yet been evaluated in detail. Notably, the magnitude of liver disease was lowered in HSC depleted mice, as expressed by reduced serum transaminases, neutrophil infiltration, tumor necrosis factor-α (TNF-α), and endothelin-A receptor in both conditions. In contrast, levels of interleukin-6 and endothelin-1 increased significantly, but only in the ischemia/reperfusion and endotoxin treatment, respectively [[1]Stewart R.K. Dangi A. Huang C. Murase N. Kimura S. Stolz D.B. et al.A novel method of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injury.J Hepatol. 2014; 60: 298-305Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar]. Endothelin-B receptor behaved differently, being unchanged (ischemia/reperfusion) or as much elevated in depleted and non-depleted mice after endotoxin treatment. The authors concluded that HSC should be major producers of TNF-α, neutrophil chemoattractant factors, and endothelin-A receptor, thus having a critical role in ischemia/reperfusion and in endotoxin induced liver injuries. Throughout years, a leading role has been ascribed to Kupffer cells (KC) in acute liver conditions [[2]Steib C.J. Gerbes A.L. Kupffer cells.in: Dufour J.-F. Clavien P.-A. Signaling pathways in liver diseases. Springer, 2010: 69-78Crossref Scopus (8) Google Scholar]. They may have been dethroned, but it is noteworthy that a recent review published in this journal, devoted to KC heterogeneity, emphasized the crosstalk between HSC and KC, with mutual activation among these cells [[3]Tacke F. Zimmermann H.W. Macrophage heterogeneity in liver injury and fibrosis.J Hepatol. 2014; 60: 1090-1096Abstract Full Text Full Text PDF PubMed Scopus (650) Google Scholar]. In this vein, we may wonder if the depletion of HSC could drive KC into a less inflammatory phenotype. In recent years, we have been committed to the quantitative study of liver, establishing that HSC and KC comprise 6.4 and 8.9% of liver cells, respectively [[4]Santos M. Marcos R. Santos N. Malhão F. Monteiro R.A.F. Rocha E. An unbiased stereological study on subpopulations of rat liver macrophages and on their numerical relation with the hepatocytes and stellate cells.J Anat. 2009; 214: 744-751Crossref PubMed Scopus (17) Google Scholar]. More recently, we used optical disectors (20 μm height), that grant unbiased estimation of number [[5]Marcos R. Monteiro R.A.F. Rocha E. The use of design-based stereology to evaluate volumes and numbers in the liver: a review with practical guidelines.J Anat. 2012; 220: 303-317Crossref PubMed Scopus (49) Google Scholar], and concluded that 42 ± 7% of HSC were vicinal to KC (Fig. 1). It should be stressed that such juxtaposition only stands out in thick sections encompassing the size of both cells (even so, some appear in Supplementary Fig. 4 of Stewart et al. [[1]Stewart R.K. Dangi A. Huang C. Murase N. Kimura S. Stolz D.B. et al.A novel method of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injury.J Hepatol. 2014; 60: 298-305Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar]). Besides paracrine stimuli, such juxtaposition should favor the crosstalk and mutual activation between cells, contacting through fenestrae of sinusoidal endothelial cells. It is well established that co-culture with KC or their conditioned medium stimulates the activation of HSC [3Tacke F. Zimmermann H.W. Macrophage heterogeneity in liver injury and fibrosis.J Hepatol. 2014; 60: 1090-1096Abstract Full Text Full Text PDF PubMed Scopus (650) Google Scholar, 6De Minicis S. Seki E. Uchinami H. Kluwe J. Zhang Y. Brenner D.A. et al.Gene expression profiles during hepatic stellate cell activation in culture and in vivo.Gastroenterology. 2007; 132: 1937-1946Abstract Full Text Full Text PDF PubMed Scopus (362) Google Scholar] and some functions, e.g., selective killing of HSC, only occur when juxtaposition with KC takes place [[7]Fischer R. Cariers A. Reinehr R. Haussinger D. Caspase 9-dependent killing of hepatic stellate cells by activated Kupffer cells.Gastroenterology. 2002; 123: 845-861Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar]. Nowadays it is recognized that different subsets of KC coexist in the liver [3Tacke F. Zimmermann H.W. Macrophage heterogeneity in liver injury and fibrosis.J Hepatol. 2014; 60: 1090-1096Abstract Full Text Full Text PDF PubMed Scopus (650) Google Scholar, 8Kinoshita M. Uchida T. Sato A. Nakashima H. Shono S. Habu Y. et al.Characterization of two F4/80-positive Kupffer cells subsets by their function and phenotype in mice.J Hepatol. 2010; 53: 903-910Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar, 9Chang J. Hisamatsu T. Shimamura K. Yoneno K. Adachi M. Naruse H. et al.Activated hepatic stellate cells mediate the differentiation of macrophages.Hepatol Res. 2013; 43: 658-669Crossref PubMed Scopus (41) Google Scholar] and a recent study showed that HSC conditioned medium favored the differentiation of pro-inflammatory macrophages [[9]Chang J. Hisamatsu T. Shimamura K. Yoneno K. Adachi M. Naruse H. et al.Activated hepatic stellate cells mediate the differentiation of macrophages.Hepatol Res. 2013; 43: 658-669Crossref PubMed Scopus (41) Google Scholar]. Stewart et al. [[1]Stewart R.K. Dangi A. Huang C. Murase N. Kimura S. Stolz D.B. et al.A novel method of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injury.J Hepatol. 2014; 60: 298-305Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar] reported that the depletion treatment had no effect on KC, but we may hypothesize that the loss of HSC-KC juxtaposition (and of paracrine stimuli by HSC) could promote a switch of KC activation, lowering their inflammatory response. Hypothetically, a CD68+ KC phenotype could emerge, attracting less neutrophils and producing less TNF-α [[8]Kinoshita M. Uchida T. Sato A. Nakashima H. Shono S. Habu Y. et al.Characterization of two F4/80-positive Kupffer cells subsets by their function and phenotype in mice.J Hepatol. 2010; 53: 903-910Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar]. Considering that KC predominantly express endothelin-B receptors [[10]Stephenson K. Harvey S.A. Mustafa S.B. Eakes A.T. Olson M.S. Endothelin association with the cultured rat Kupffer cell: characterization and regulation.Hepatology. 1995; 22: 896-905PubMed Google Scholar], this would also justify the puzzling pattern of endothelin-A vs. B receptors. In conclusion, the KC phenotype shift hypothesis would partially explain the data presented by Stewart et al. [[1]Stewart R.K. Dangi A. Huang C. Murase N. Kimura S. Stolz D.B. et al.A novel method of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injury.J Hepatol. 2014; 60: 298-305Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar], being alternative (or complementary) to the view of HSC as having a critical role in acute liver conditions. This hypothesis deserves further attention from future studies using the HSC depletion method in acute liver injuries. The whole liver may be viewed as an orchestra, with well-defined string, woodwind, and brass instruments (hepatocytes, KC, and HSC in this metaphor). If in vitro studies produce simpler tunes (one or two instruments), the methodology presented by Stewart et al. [[1]Stewart R.K. Dangi A. Huang C. Murase N. Kimura S. Stolz D.B. et al.A novel method of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injury.J Hepatol. 2014; 60: 298-305Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar] creates a much more complex and appealing symphony. However, we are only starting to hear the melody, and still not know if all brass instruments are alike, which are missing and how the orchestra will hold without them. The author declares that he does not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.