Liver Resident Macrophages (Kupffer Cells) Share Several Functional Antigens in Common with Endothelial Cells

Fragment-sequencing unveils local tissue microenvironments at single-cell resolution

Cells collectively determine biological functions by communicating with each other-both through direct physical contact and secreted factors. Consequently, the local microenvironment of a cell influences its behavior, gene expression, and cellular crosstalk. Disruption of this microenvironment causes reciprocal changes in those features, which can lead to the development and progression of diseases. Hence, assessing the cellular transcriptome while simultaneously capturing the spatial relationships of cells within a tissue provides highly valuable insights into how cells communicate in health and disease. Yet, methods to probe the transcriptome often fail to preserve native spatial relationships, lack single-cell resolution, or are highly limited in throughput, i.e. lack the capacity to assess multiple environments simultaneously. Here, we introduce fragment-sequencing (fragment-seq), a method that enables the characterization of single-cell transcriptomes within multiple spatially distinct tissue microenvironments. We apply fragment-seq to a murine model of the metastatic liver to study liver zonation and the metastatic niche. This analysis reveals zonated genes and ligand-receptor interactions enriched in specific hepatic microenvironments. Finally, we apply fragment-seq to other tissues and species, demonstrating the adaptability of our method.

The polarizable and reprogrammable identity of Kupffer cells in Nonalcoholic Steatohepatitis

Kupffer cells (KCs) are the resident macrophages of the liver with similar origins to myeloid-derived macrophages. Once differentiated, KCs exhibit distinct cellular machinery capable of longevity and self-renewal, making them a crucial player in promoting effective intrahepatic communication. However, this gets compromised in disease states like Nonalcoholic Steatohepatitis (NASH), where the loss of embryo-derived KCs (EmKCs) is observed. Despite this, other KC-like and KC-derived populations start to form and contribute to a variety of roles in NASH pathogenesis, often adopting a NASH-associated molecular signature. Here we offer a brief overview of recent reports describing KC polarization and reprogramming in the liver. We describe the complexities of KC cellular identity, their proposed ability to reprogram to fibroblast-like and endothelial-like cells, and the potential implications in NASH.

A subset of Kupffer cells regulates metabolism through the expression of CD36

Tissue macrophages are immune cells whose phenotypes and functions are dictated by origin and niches. However, tissues are complex environments, and macrophage heterogeneity within the same organ has been overlooked so far. Here, we used high-dimensional approaches to characterize macrophage populations in the murine liver. We identified two distinct populations among embryonically derived Kupffer cells (KCs) sharing a core signature while differentially expressing numerous genes and proteins: a major CD206^loESAM^- population (KC1) and a minor CD206^hiESAM⁺ population (KC2). KC2 expressed genes involved in metabolic processes, including fatty acid metabolism both in steady-state and in diet-induced obesity and hepatic steatosis. Functional characterization by depletion of KC2 or targeted silencing of the fatty acid transporter Cd36 highlighted a crucial contribution of KC2 in the liver oxidative stress associated with obesity. In summary, our study reveals that KCs are more heterogeneous than anticipated, notably describing a subpopulation wired with metabolic functions.

Hepatic infarction, hematoma, and rupture in HELLP syndrome: support for a vasospastic hypothesis

Purpose: HELLP syndrome is a relatively uncommon pregnancy-related condition characterized by hemolysis, elevated liver function tests, and low platelets. It can be accompanied by life-threatening hepatic complications including hepatic infarction, hematoma formation, and hepatic rupture. HELLP syndrome occurs in approximately 0.2% of pregnancies. Major hepatic complications occur in less than 1% of HELLP patients suggesting an incidence of 1/50,000. The pathogenesis is incompletely understood and in particular, it is difficult to understand a disorder with both major thrombotic and bleeding manifestations.Methods: Literature review.Results: On the basis of reports in the published literature, and our own clinical experience, we suggest that vasospasm is one of the principal drivers with hepatic ischemia, infarction, and hemorrhage as secondary events. It is known that vasoactive substances are released by the failing placenta. We suggest these cause severe vasospasm, most likely affecting the small post-sinusoidal hepatic venules. This leads to patchy or confluent hepatic ischemia and/or necrosis with a resultant increase in circulating liver enzymes. Reperfusion is associated with a fall in platelet count and microvascular hemorrhage if the microvasculature is infarcted. Blood tracks to the subcapsular space causing hematoma formation. If the hematoma ruptures the patient presents with severe abdominal pain, intra-abdominal hemorrhage, and shock.Conclusions: We suggest that hepatic and other complications associated with HELLP syndrome including placental abruption, acute renal failure, and posterior reversible encephalopathy syndrome (PRES) may also be due to regional vasospasm.

Cell-type-resolved alternative splicing patterns in mouse liver

Alternative splicing (AS) is an important post-transcriptional regulatory mechanism to generate transcription diversity. However, the functional roles of AS in multiple cell types from one organ have not been reported. Here, we provide the most comprehensive profile for cell-type-resolved AS patterns in mouse liver. A total of 13,637 AS events are detected, representing 81.5% of all known AS events in the database. About 46.2% of multi-exon genes undergo AS from the four cell types of mouse liver: hepatocyte, liver sinusoidal endothelial cell, Kupffer cell and hepatic stellate cell, which regulates cell-specific functions and maintains cell characteristics. We also present a cell-type-specific splicing factors network in these four cell types of mouse liver, allowing data mining and generating knowledge to elucidate the roles of splicing factors in sustaining the cell-type-specialized AS profiles and functions. The splicing switching of Tak1 gene between different cell types is firstly discovered and the specific Tak1 isoform regulates hepatic cell-type-specific functions is verified. Thus, our work constructs a hepatic cell-specific splicing landscape and reveals the considerable contribution of AS to the cell type constitution and organ features.

Possible Involvement of Liver Resident Macrophages (Kupffer Cells) in the Pathogenesis of Both Intrahepatic and Extrahepatic Inflammation

Liver resident macrophages designated Kupffer cells (KCs) form the largest subpopulation of tissue macrophages. KCs are involved in the pathogenesis of liver inflammation. However, the role of KCs in the systemic inflammation is still elusive. In this study, we examined whether KCs are involved in not only intrahepatic inflammation but also extrahepatic systemic inflammation. Administration of clodronate liposomes resulted in the KC deletion and in the suppression of liver injury in T cell-mediated hepatitis by ConA as a local acute inflammation model, while the treatment did not influence dextran sulfate sodium- (DSS-) induced colitis featured by weight loss, intestinal shrink, and pathological observation as an ectopic local acute inflammation model. In contrast, KC deletion inhibited collagen-induced arthritis as a model of extrahepatic, systemic chronical inflammation. KC deleted mice showed weaker arthritic scores, less joint swelling, and more joint space compared to arthritis-induced control mice. These results strongly suggest that KCs are involved in not only intrahepatic inflammatory response but also systemic (especially) chronic inflammation.