LKB1 Regulates Vascular Macrophage Functions in Atherosclerosis

Liver kinase B1 (LKB1) is known to shape the regulation of macrophage function by participating in multiple processes including cell metabolism, growth, and polarization. However, whether LKB1 also affects the functional plasticity of macrophages in atherosclerosis has not attracted much attention. Abnormal macrophage function is a pathophysiological hallmark of atherosclerosis, characterized by the formation of foam cells and the maintenance of vascular inflammation. Mounting evidence supports that LKB1 plays a vital role in the regulation of macrophage function in atherosclerosis, including affecting lipid metabolism reprogramming, inflammation, endoplasmic reticulum stress, and autophagy in macrophages. Thus, decreased expression of LKB1 in atherosclerosis aggravates vascular injury by inducing excessive lipid deposition in macrophages and the formation of foam cells. To systematically understand the role and potential mechanism of LKB1 in regulating macrophage functions in atherosclerosis, this review summarizes the relevant data in this regard, hoping to provide new ideas for the prevention and treatment of atherosclerosis.

STK11/LKB1 Modulation of the Immune Response in Lung Cancer: From Biology to Therapeutic Impact

The STK11/LKB1 gene codes for liver kinase B1 (STK11/LKB1), a highly conserved serine/threonine kinase involved in many energy-related cellular processes. The canonical tumor-suppressive role for STK11/LKB1 involves the activation of AMPK-related kinases, a master regulator of cell survival during stress conditions. In pre-clinical models, inactivation of STK11/LKB1 leads to the progression of lung cancer with the acquisition of metastatic properties. Moreover, preclinical and clinical data have shown that inactivation of STK11/LKB1 is associated with an inert tumor immune microenvironment, with a reduced density of infiltrating cytotoxic CD8+ T lymphocytes, a lower expression of PD-(L)1, and a neutrophil-enriched tumor microenvironment. In this review, we first describe the biological function of STK11/LKB1 and the role of its inactivation in cancer cells. We report descriptive epidemiology, co-occurring genomic alterations, and prognostic impact for lung cancer patients. Finally, we discuss recent data based on pre-clinical models and lung cancer cohorts analyzing the results of STK11/LKB1 alterations on the immune system and response or resistance to immune checkpoint inhibitors.

The Loss of Liver Kinase B1 Accelerates Maturation Time in the Developing Erythrocyte

In the US, iron-restricted anemia contributes greatly to morbidity. The erythroid iron deprivation response, characterized by a pathway in which erythropoiesis is suppressed during iron restriction, underlies this anemia. In preliminary studies, liver kinase B1 (LKB1) was implicated as a potential key component in the erythroid iron deprivation response. Normal human CD34+ hematopoietic progenitor cells cultured for 3 days in erythroid medium with 100% or 10% transferrin saturations underwent immunoblot of whole cell lysates. Reproducibly, the levels of LKB1 did not change based on the transferrin saturation; however, immunofluorescence imaging showed a shift in subcellular localization when cells were subjected to low iron conditions. To assess the effects of LKB1 loss in the erythroid compartment, we used control and LKB1 conditional knockout (STK11 F/F; EpoR-Cre+) mice. In steady-state conditions, the loss of LKB1 does not confer a change in RBC count, though, there is a baseline increase in the number of reticulocytes, and a large increase in the level of serum Erythropoietin (Epo). In a model to precipitate anemia, these mice were challenged with intraperitoneal injection of phenylhydrazine (PHZ). It was found that LKB1 is dispensable for an appropriate response to this type of stress erythropoiesis. To assess the impact of LKB1 on maturation, we performed flow cytometric analysis using an ex vivo culture system of splenic erythroblasts. LKB1-deficient erythroid progenitors show increased percentages of more advanced cells as evidenced by the surface markers CD71 and Ter119 (the mouse analogue of human glycophorin A). Current studies are underway to assess if this change is due to signaling through the AMPK pathway. These studies will provide mechanistic detail of LKB1 function and activity on erythropoiesis, improving our understanding of programs involved in maturation of differentiation and lineage selection which may ultimately help to improve health outcomes and advance treatment for various types of anemias. Disclosures No relevant conflicts of interest to declare.

Hotspots and trends in liver kinase B1 research: A bibliometric analysis

Introduction In the past 22 years, a large number of publications have reported that liver kinase B1 (LKB1) can regulate a variety of cellular processes and play an important role in many diseases. However, there is no systematic bibliometric analysis on the publications of LKB1 to reveal the research hotspots and future direction. Methods Publications were retrieved from the Web of Science Core Collection (WoSCC), Scopus, and PubMed databases. CiteSpace and VOSviewer were used to analysis the top countries, institutions, authors, source journals, discipline categories, references, and keywords. Results In the past 22 years, the number of LKB1 publications has increased gradually by year. The country, institution, author, journals that have published the most articles and cited the most frequently were the United States, Harvard University, Prof. Benoit Viollet, Journal of Biochemistry and Plos One. The focused research hotspot was the molecular functions of LKB1. The emerging hotspots and future trends are the clinical studies about LKB1 and co-mutated genes as biomarkers in tumors, especially in lung adenocarcinoma. Conclusions Our research could provide knowledge base, frontiers, emerging hotspots and future trends associated with LKB1 for researchers in this field, and contribute to finding potential cooperation possibilities.

LKB1 signalling in dendritic cells controls whole-body metabolic homeostasis by limiting T helper 17 priming

Obesity-associated metaflammation drives the development of insulin resistance and type 2 diabetes, notably through modulating innate and adaptive immune cells in metabolic organs. The nutrient sensor liver kinase B1 (LKB1) has recently been shown to control cellular metabolism and T cell priming functions of dendritic cells (DCs). Here, we report that hepatic DCs from high-fat diet (HFD)-fed obese mice display increased LKB1 phosphorylation and that LKB1 deficiency in DCs (CD11cΔLKB1) worsened HFD-driven hepatic steatosis, systemic insulin resistance and glucose intolerance. Loss of LKB1 in DCs was associated with increased cellular expression of Th17-polarizing cytokines and increased hepatic CD4+ IL-17A+ Th17 cells in HFD-fed mice. Importantly, IL-17A neutralization rescued metabolic perturbations in HFD-fed CD11cΔLKB1 mice. Mechanistically, disrupted metabolic homeostasis was independent of the canonical LKB1-AMPK axis. Instead, we provide evidence for involvement of the AMPK-related salt-inducible kinase(s) in controlling Th17-polarizing cytokine expression in LKB1-deficient DCs. Altogether, our data reveal a key role for LKB1 signalling in DCs in protection against obesity-induced metabolic dysfunctions by limiting hepatic Th17 differentiation.

LKB1 Regulates Goat Intramuscular Adipogenesis Through Focal Adhesion Pathway

Intramuscular fat (IMF) deposition is one of the most important factors to affect meat quality in livestock and induce insulin resistance and adverse metabolic phenotypes for humans. However, the key regulators involved in this process remain largely unknown. Although liver kinase B1 (LKB1) was reported to participate in the development of skeletal muscles and classical adipose tissues. Due to the specific autonomic location of intramuscular adipocytes, deposited between or within muscle bundles, the exact roles of LKB1 in IMF deposition need further verified. Here, we cloned the goat LKB1 coding sequence with 1,317 bp, encoding a 438 amino acid peptide. LKB1 was extensively expressed in detected tissues and displayed a trend from decline to rise during intramuscular adipogenesis. Functionally, knockdown of LKB1 by two individual siRNAs enhanced the intramuscular preadipocytes differentiation, accompanied by promoting lipid accumulation and inducing adipogenic transcriptional factors and triglyceride synthesis-related genes expression. Conversely, overexpression of LKB1 restrained these biological signatures. To further explore the mechanisms, the RNA-seq technique was performed to compare the difference between siLKB1 and the control group. There were 1,043 differential expression genes (DEGs) were screened, i.e., 425 upregulated genes and 618 downregulated genes in the siLKB1 group. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis predicted that the DEGs were mainly enriched in the focal adhesion pathway and its classical downstream signal, the PI3K-Akt signaling pathway. Specifically, knockdown of LKB1 increased the mRNA level of focal adhesion kinase (FAK) and vice versa in LKB1-overexpressed cells, a key component of the activated focal adhesion pathway. Convincingly, blocking this pathway by a specific FAK inhibitor (PF573228) rescued the observed phenotypes in LKB1 knockdown adipocytes. In conclusion, LKB1 inhibited goat intramuscular adipogenesis through the focal adhesion pathway. This work expanded the genetic regulator networks of IMF deposition and provided theoretical support for improving human health and meat quality from the aspect of IMF deposition.

Spatial regulation of AMPK signaling revealed by a sensitive kinase activity reporter

AMP-activated protein kinase (AMPK) is a master regulator of cellular energetics which coordinates metabolism by phosphorylating a plethora of substrates throughout the cell. But whether AMPK activity is regulated at different subcellular locations to provide precise spatial and temporal control over metabolism is unclear. Genetically encoded AMPK activity reporters (AMPKAR) have provided a window into spatial AMPK activity, but the limited dynamic range of current AMPKARs hinders detailed study. To monitor the dynamic activity of AMPK with high sensitivity, we developed a single-fluorophore AMPK activity reporter (ExRai AMPKAR) that exhibits an excitation ratiometric fluorescence change upon phosphorylation by AMPK, with over 3-fold greater response compared to previous AMPKARs. Using subcellularly localized ExRai AMPKAR, we found that the activity of AMPK at the lysosome and mitochondria are differentially regulated. While different activating conditions, irrespective of their effects on ATP, robustly yet gradually increase mitochondrial AMPK activity, lysosomal AMPK activity accumulates with much faster kinetics. Genetic deletion of the canonical upstream kinase liver kinase B1 (LKB1) resulted in slower AMPK activity at lysosomes but did not affect the response amplitude at either location, in sharp contrast to the necessity of LKB1 for maximal cytoplasmic AMPK activity. We further discovered AMPK activity in the nucleus, which resulted from LKB1-mediated cytoplasmic activation of AMPK followed by nuclear shuttling. Thus, a new, sensitive reporter for AMPK activity, ExRai AMPKAR, in complement with mathematical and biophysical methods, captured subcellular AMPK activity dynamics in living cells and unveiled complex regulation of AMPK signaling within subcellular compartments.

Gene of the month: STK11

STK11 encodes for the protein liver kinase B1, a serine/threonine kinase which is involved in a number of physiological processes including regulation of cellular metabolism, cell polarity and the DNA damage response. It acts as a tumour suppressor via multiple mechanisms, most classically through AMP-activated protein kinase-mediated inhibition of the mammalian target of rapamycin signalling pathway. Germline loss-of-function mutations in STK11 give rise to Peutz-Jeghers syndrome, which is associated with hamartomatous polyps of the gastrointestinal tract, mucocutaneous pigmentation and a substantially increased lifetime risk of many cancers. In the sporadic setting, STK11 mutations are commonly seen in a subset of adenocarcinomas of the lung in addition to a number of other tumours occurring at various sites. Mutations in STK11 have been associated with worse prognoses across a range of malignancies and may be a predictor of poor response to immunotherapy in a subset of lung cancers, though further studies are needed before the presence of STK11 mutations can be implemented as a routine clinical biomarker.