Protective role of OPN-High macrophages in NASH

非酒精性脂肪性肝炎（NASH）正在成为全球儿童和成人肝脏疾病的主要原因。最近的研究表明，NASH期间浸润肝脏的巨噬细胞（MFs）的表型存在很大的异质性。募集的MFs分为两个亚群，具有不同的激活状态：(1)非常类似于稳态库普弗细胞（KCs），或(2)脂质相关的MFs （lam）。2020年，在NASH患者的肝脏中发现了一组骨桥蛋白（OPN）高表达的lam。值得注意的是，与常驻细胞和单核细胞来源的KCs相比，lam具有不同的活化能力，并且具有独特的脂质代谢能力。然而，它们是否也与邻近细胞串扰，以防止NASH中的脂肪变性和纤维化，仍然未知。虽然MFs进入肝脏以及随后的激活被认为是促炎和促纤维化事件，但目前一个重要的知识缺口是缺乏对OPNHigh MFs在NASH中是有害还是保护的理解。初步数据表明Spp1KI Mye受到保护，而Spp1ΔMye的NASH活性评分低于WT小鼠。因此，我们的研究结果提示了一种范式转变，即OPNHigh MFs可能保护NASH。然而，细胞间通讯以及OPNHigh MFs的预防和治疗潜力仍有待确定。我们的主要假设是，OPNHigh MFs通过向肝细胞（HEPs）和肝星状细胞（hsc）发出信号，减少肝脏脂肪变性和纤维化，并保护免受NASH的侵害。目的1是确定OPNHigh MFs如何防止脂肪变性。我们假设OPNHigh MFs信号HEPs上调精氨酸酶-2 (ARG2)，从而增加线粒体生物能量和脂肪酸氧化（FAO），减少亚硝酸盐应激，并防止脂肪变性。为了验证这一点，首先，我们将识别信号HEPs上调ARG2的OPNHigh MF“分泌组”蛋白；其次，我们将确定鉴定的OPNHigh MF分泌组蛋白如何在HEPs中反激活ARG2启动子；第三，我们将阐明ARG2如何在HEPs中增加线粒体生物能量和FAO，并减少亚硝化应激。目的2是剖析OPNHigh MFs如何防止纤维化。我们假设，在NASH中，OPNHigh MFs通过分泌组蛋白发出信号，降低胶原- i，和/或改变“基质”景观，以防止纤维化和调节细胞行为。为了证明这一点，首先，我们将确定OPNHigh MF分泌组蛋白，该蛋白向造血干细胞发出信号，以降低胶原- i沉积和/或增加其降解；其次，分析OPNHigh mf是否改变基质景观，建立OPNHigh MF-ECM相关网络；第三，我们将进行肝脏scrna测序，并计算确定OPNHigh MF-ECM网络如何调节NASH中的细胞行为。

Non-alcoholic steatohepatitis (NASH) is emerging as a major worldwide cause of liver disease in children and adults. Recent studies demonstrate substantial heterogeneity in the phenotype of macrophages (MFs) infiltrating the liver during NASH. Recruited MFs exist as two subsets, with distinct activation states: (1) those closely resembling homeostatic Kupffer cells (KCs), or (2) lipid-associated MFs (LAMs). In 2020, a cluster of LAMs with high expression of osteopontin (OPN) was identified in livers with NASH. Notably, LAMs are differentially activated, compared to resident- and monocyte-derived KCs, and with a distinct ability to metabolize lipids. However, whether they also crosstalk with neighboring cells, to prevent steatosis and fibrosis in NASH, remains unknown. While recruitment of MFs into the liver, and subsequent activation, are considered proinflammatory and profibrotic events, currently a significant knowledge gap is a lack of understanding of whether OPNHigh MFs, are detrimental or protective in NASH. Preliminary data demonstrates that Spp1KI Mye are protected, whereas Spp1ΔMye have worse NASH activity scores than WT mice. Thus, our results suggest a paradigm shift, in that OPNHigh MFs may protect from NASH. Yet, the intercellular communication, and preventive and therapeutic potential of OPNHigh MFs, remain to be determined. Our overarching hypothesis is that OPNHigh MFs, by signaling to hepatocytes (HEPs) and hepatic stellate cells (HSCs), reduce liver steatosis and fibrosis, and protect from NASH. Aim 1 is to identify how OPNHigh MFs protect from steatosis. We hypothesize that OPNHigh MFs signal HEPs to upregulate arginase-2 (ARG2), which increases mitochondrial bioenergetics and fatty acid oxidation (FAO), reduces nitrosative stress, and protects from steatosis. To test this, first, we will identify the OPNHigh MF ‘secretome’ proteins that signal HEPs to upregulate ARG2; second, we will determine how the identified OPNHigh MF secretome proteins transactivate the ARG2 promoter, in HEPs; and third, we will elucidate how ARG2 increases mitochondrial bioenergetics and FAO, and reduces nitrosative stress, in HEPs. Aim 2 is to dissect how OPNHigh MFs protect from fibrosis. We hypothesize that OPNHigh MFs signal through secretome proteins to lower collagen-I, and/or modify the ‘matrisome’ landscape, to prevent fibrosis, and regulate cell behavior, in NASH. To prove this, first, we will identify the OPNHigh MF secretome proteins that signal HSCs to lower collagen-I deposition and/or increase its degradation; second, we will analyze whether OPNHigh MFs modify the matrisome landscape, and establish the OPNHigh MF-ECM correlation network; and third, we will perform liver scRNA-seq, and computationally identify how the OPNHigh MF-ECM network regulates cell behavior in NASH.