Mast cells in liver disease progression: An update on current studies and implications

INTRODUCTION

Mast cells (MCs) are innate immune cells originating from CD34⁺/CD117⁺ hematopoietic stem cells and regulate liver disease progression.^[1] With a variety of surface receptors, MC activation is triggered by two main receptor-dependent pathways: IgE/high-affinity receptor for the Fc region of IgE (FcεRI) and IL-33/suppressor of tumorigenicity 2 (ST2).^[2] Upon liver damage, MCs degranulate releasing mediators, including preformed bioactive metabolites (histamine, tryptase, and chymase), newly synthesized cytokines (TGF-β, TNF-α, and IL-1β), and de novo lipid mediators (leukotriene B4, leukotriene D4, prostaglandin)^[3] (Figure 1). TGF-β1, TNF-α, IL-6, IL-10, and synaptophysin 9 (SYP-9) are released upon liver damage by paracrine interactions between MCs and hepatocytes (through TGF-β, ^[4]TNF-α^[5]), cholangiocytes (through IL-10, TGF-β^[6]), HSCs (through SYP-9, TGF-β1^[7]), and Kupffer cells (through TNF-α, IL-6^[8]). This review encompasses the most recent studies involving MCs, their mediators, and the impact on liver disease.

FIGURE 1.

Diseases implicated by increased MC presence/activation. Immature MC progenitors circulate in the lymphatic and vascular systems and develop to the mature form once they reach the peripheral organs upon activation through IgE/FcεRI and IL-33/ST2 receptor-dependent pathways. MC implication has been demonstrated in a diverse spectrum of liver disease (HCC, CCA, ALD/NAFLD, PBC, PSC) through increased MC presence/infiltration; elevated secretion of histamine, tryptase, and chymase; up-regulated expression of TGF-β, TNF-α, and IL-17; and activation of three principal MC-mediated signaling pathways including HDC/histamine/HRs, SCF/TGF-β1, and miR-144-3p/ALDH1A3

DISEASES IMPLICATED BY MC PRESENCE/ACTIVATION

MCs and hepatocellular carcinoma (HCC)

MC integration in HCC occurs through the IL family, histamine and regulation of histamine receptors (HRs), tryptase-positive and chymase-positive MCs, and MC-derived exosomes (Figure 1). Three subgroups of 329 patients with HCC were identified based on tumor microenvironment and infiltration of 22 immune cells (including resting and activated MCs) using CIBERSORT software and the ConsensuClusterPlus package.^[9] Decreased resting MCs in patients with HCC and fibrosis compared to controls was reported based on the immune cell landscape calculated by CEBERSORT.^[10]

Increased expression of IL-17 and IL-17 receptor^[11] and decreased expression of IL-36α^[12] correlated with poor HCC prognosis. MC-derived histamine stimulates the growth of human HCC cell lines, and inhibition of histamine H1 receptor (H1HR)/H2HR attenuates HCC proliferation.^[13] Up-regulation H1HR^[14] or H3HR^[15] enhances HCC cell growth and metastasis. H3HR expression is elevated in HCC, promoting cell growth and survival through protein kinase/cyclic adenosine monophosphate responsive element-binding/cyclin-dependent kinase inhibitor p21 signaling.^[16] The increase of tryptase-positive and chymase-positive MCs in human HCC^[17] and the decrease in tryptase serum level in patients with HCC after hepatic transarterial chemoembolization^[18] suggest a role for these as biomarkers. The majority of MCs in HCC are inactive, and resting MC density is elevated in 305 HCC livers using tryptase immunohistochemistry.^[19]

MCs and cholangiocarcinoma (CCA)

CCA/MC involvement was demonstrated by increased activity of tryptase and chymase through 1-histidine decarboxylase (HDC)/histamine/HR signaling (Figure 1). Increased tryptase and chymase expression in xenograft tumor samples was reversed by cromolyn sodium.^[20] In patients with CCA, tryptase-positive MC infiltration^[21] and chymase activity in bile^[22] increased. Histamine promotes cholangiocyte proliferation,^[7,23] and inhibition of MC-derived histamine attenuated CCA growth in xenograft tumors through a stem cell factor (SCF) receptor (c-Kit)/SCF–dependent pathway.^[20] Treatment with cromolyn sodium decreased MC numbers, proliferating cell nuclear antigen expression, and CCA.^[23] MC presence, histamine serum levels, and HDC expression increased in human patients with CCA and xenograft tumors, which was blocked by HDC or H1HR inhibition.^[24] Blocking HDC and H1HR suppressed histamine release and cellular proliferation,^[25] whereas up-regulation of H3HR through protein kinase Cα^[26] and overexpression of H4HR^[27] stunted CCA growth.

MCs and alcohol-associated liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD)

The link between MCs and ALD is demonstrated by increased activity of tryptase-positive and chymase-positive MCs and MC-derived TNF-α (Figure 1). Tryptase-positive and chymase-positive MC density increased in ALD liver biopsies.^[28] In ethanol-induced hepatoxicity, MC density and inflammatory markers, including nuclear factor binding near the kappa light chain gene in B cells, were elevated.^[29] This corroborated with lipid accumulation as the first response to alcohol abuse after binding of MC-secreted TNF-α to hepatocyte TNF receptors,^[5] implicating TNF-α as a common factor between hepatocytes and MCs.

MC implications in NAFLD/non-alcoholic steatohepatitis (NASH), a significant indication for liver transplant, are focused on enhanced MC presence, MC-secreted chymase, and HDC/histamine signaling (Figure 1). Increased tryptase-positive MCs in the periportal and parenchymal regions of patients with stage 3–4 NASH^[30] was described. Elevated MC presence promoted NAFLD to NASH progression by up-regulation of aldehyde dehydrogenase 1 family, member A3 (ALDH1A3) and concurrent down-regulation of microRNA-144–3 prime (miR-144-3p) in human NASH livers and wild-type (WT) mice fed a Western diet.^[31] Western diet–fed, MC-deficient Kit^W-sh mice had ameliorated NAFLD phenotypes, along with a switch to macrovesicular steatosis.^[31] Apolipoprotein E–deficient (ApoE^−/−) and MC-deficient (Kit^W-sh/W-sh) mice displayed reduced hepatic steatosis and IL production compared to ApoE^−/− mice, demonstrating a protective role in the absence of MCs.^[32] Chymase activity, matrix metalloproteinase level, and TGF-β level were attenuated in a high-fat and high-cholesterol model treated with TY-51469 (chymase inhibitor).^[33] Enhancement in MC chymase activity in NASH was observed,^[34] and TY-51469 treatment reduced hepatic steatosis and fibrosis by decreasing angiotensin II, collagen (Col) I, Col III, and α-smooth muscle actin (α-SMA) expression.^[35] A high-fat diet decreased intrahepatic bile duct mass (IBDM) and cholangiocyte senescence in Hdc^−/− mice through dysregulated histamine/leptin signaling, evidenced by reduced histamine secretion and increased leptin resistance, suggesting the importance of HDC/histamine signaling in obesity-induced liver damage.^[36]

MCs and primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC)

Portal MC infiltration, plasma histamine level, density of hepatic tryptase-positive and chymase-positive MCs, and liver chymase concentration increased in patients with PBC^[1] (Figure 1). Ketotifen, an MC stabilizer, increased hepatic mucosal MC presence in cholestatic rats while decreasing the MC population in the mesenteric lymphatic complex and levels of TGF-β1 and VEGF.^[37]

The interplay between MCs and PSC is mediated through the HDC/histamine/HRs and SCF/TGF-β1 axes (Figure 1). A reduction in MC-derived histamine, IBDM, and VEGF expression was observed in bile duct ligated (BDL) Hdc^−/− compared to BDL WT mice, indicating a link between HDC and histamine in PSC.^[38] This correlated with amelioration of hepatic damage and fibrosis in the double knockout (DKO) mouse model combining multidrug resistance 2 (Mdr2^−/−) and HDC^−/− mice, which display attenuated phenotypes relative to Mdr2^−/− mice; and when DKO mice were treated with histamine, PSC phenotypes increased, demonstrating that histamine induces hepatic damage.^[8] Cromolyn sodium treatment reduced hepatic MC number near cholangiocytes after BDL compared to control^[23] and attenuated PSC phenotypes in Mdr2^−/− mice, which was coupled with decreased bile flow and total bile acid (TBA) content.^[7] Ursodeoxycholic acid treatment ameliorated MC-secreted histamine and biliary damage in Mdr2^−/− mice and human PSC.^[39] The differential action on biliary damage of H1/H2HR antagonists in Mdr2^−/− mice was demonstrated by reduced proliferation of small and large cholangiocytes.^[24] When Mdr2^−/− mice were treated with an H2HR vivo-morpholino, PSC phenotypes and MC activation were reduced.^[40] HRs, HDC, and serum histamine levels decreased in BDL Kit^W-sh mice relative to BDL WT mice,^[41] supporting the importance of HDC/histamine/HR signaling in cholestasis.

There is increased SCF biliary expression/secretion in human PSC, and targeting SCF using vivo-morpholino decreased MC migration, biliary damage, and fibrosis in Mdr2^−/− mice.^[42] TGF-β1 is a significant factor in PSC progression, and cromolyn sodium treatment decreases TGF-β1 levels in cholestatic rodents.^[6,7,23] In DKO mice treated with histamine, TGF-β1 signaling was enhanced, demonstrating that histamine directly impacts TGF-β1.^[8] MC activation in Mdr2^−/− mice increased fibrosis, as evidenced by elevated expression of TGF-β1, α-SMA, fibronectin, and Col I.^[7,24] Enhanced fibrosis was ameliorated in BDL Kit^W-sh mice compared to BDL WT mice.^[41] Reintroduction of MCs lacking TGF-β1 into WT, DKO, or Kit^W-sh mice reduced PSC phenotypes compared to control MC injections.^[43] When MCs lacked farnesoid X receptor signaling, mice had significantly decreased TBA levels and PSC phenotypes compared to mice injected with control MCs.^[44] These studies demonstrate that manipulation of MCs in vitro impacts in vivo phenotypes and supports the role of SCF/TGF-β1 signaling in PSC.

CONCLUSIONS/FUTURE PERSPECTIVES

The dynamic interplay between MCs and liver diseases is highlighted by increased MC infiltration, elevated MC-secreted bioactive metabolites, MC-derived cytokines, and the regulation of key signaling pathways such as HDC/histamine/HRs, SCF/TGF-β1, and miR-144-3p/ALDH1A3. In addition to antihistamines, MC stabilizers, and tryptase/chymase inhibitors, natural compounds have emerged as promising approaches to target MCs in liver disease (Table 1). Further studies are required to elucidate the crosstalk between MCs and resident liver cells and to understand MC activation and infiltration mechanisms in liver diseases.

TABLE 1.

Compounds targeting MCs in liver disease

Name	Function	Disease/effects	Models	Reference no./year
Mepyramine/ranitidine	H1HR antagonist	PSC/reducing tumor growth, serum histamine, angiogenesis, and EMT	Mdr2−/− male mice	[24]/2018
	H2HR antagonist
Cimetidine	H2HR antagonist	Hepatic ischemia–reperfusion injury/protective effect by inhibiting the activity of P450 and decreasing the generation of endogenous ROS	Rat hepatocytes BRL-3A cell +24-h hypoxia +4-h reoxygenation	[45]/2013
RAMH	H3HR agonist	CCA/inhibiting CCA growth by activating PKCα	CCA cell lines	[26]/2009
			BALB/c nude mice
Clobenpropit	H4HR agonist	CCA/decreasing CCA proliferation through Ca2+-dependent pathway	Xenograft mice injected with Mz-ChA-1 cells	[27]/2011
Cromolyn sodium	MC stabilizer	PSC/ameliorating cholangiocyte proliferation, bile flow and MC infiltration by decreasing HDC expression and histamine secretion	Mdr2−/− mice	[7]/2016
			BDL male rats	[23]/2014
			MC line	[6]/2016
Ketotifen	MC stabilizer	Hepatotoxicity caused by CYC/ameliorate effects by decreasing oxidative stress, inflammation, and apoptosis	Albino Wistar rats	[46]/2020
			Adult male injected with CYC
Doxantrazole	MC stabilizer	Alcohol hepatic toxicity/protective effects by impairing the intestinal barrier permeability	Sprague-Dawley rats + ethanol + dextrose	[47]/2006
TY-51469	Chymase inhibitor	NASH/ameliorating hepatic steatosis and fibrosis by attenuating the MC presence and expression of Col I, Col III, and α-SMA	MCD diet-fed hamsters	[34]/2010
TY-51469	Chymase inhibitor	NASH/ameliorating hepatic steatosis and fibrosis by attenuating the expression of TGF-β, angiotensin II, and MMP-9	HFC diet–fed rats	[33]/2017
APC 366	Tryptase inhibitor	PSC/reducing hepatic fibrosis, collagen content, and expression of PAR-2 and α-SMA	BDL rats + APC 366	[48]/2014
UDCA	Natural bile acid	PSC/ameliorating biliary damage, fibrosis, and inflammation by reducing MC activation	Human PSC	[39]/2018
			Mdr2−/− mice
Zingerone	Bioactive ingredient extracted from ginger root	ALD/ameliorating hepatoxicity by decreasing MC density and expression of NFκB, COX-2, TNF-α, and IL-6	Male albino Wistar rats post–orally supplemented 30% ethanol for 60 days	[29]/2016

Abbreviations: COX-2, cyclooxygenase-2; CYC, cyclophosphamide (common chemotherapeutic agent); EMT, epithelial–mesenchymal transition; HFC, high fat and high cholesterol; MCD, methionine and choline–deficient; MMP-9, matrix metalloproteinase; PAR-2, protease-activated receptor 2; PKC, protein kinase C; RAMH, (R)-(α)-(–)-methylhistamine dihydrobromide; ROS, reactive oxygen species; UDCA, ursodeoxycholate.

Abbreviations:

α-SMA

α-smooth muscle actin

ALD

alcohol-associated liver disease

ALDH1A3

aldehyde dehydrogenase 1 family, member A3

BDL

bile duct ligation

CCA

cholangiocarcinoma

Col

collagen

DKO

double knockout

FcεRI

high-affinity receptor for the Fc region of IgE

H1/2/3/4HR

histamine H1/2/3/4 receptor

HDC

1-histidine decarboxylase

HR

histamine receptor

MC

mast cell

Mdr ^−/−

multidrug resistant 2 knocked out

miR-144-3p

microribonucleic acid 144-3 prime

PBC

primary biliary cholangitis

PSC

primary sclerosing cholangitis

SCF

stem cell factor

ST2

suppressor of tumorigenicity 2

WT

wild type