Galectins and microenvironmental niches during hematopoiesis

Galectin expression detected by 68Ga-galectracer PET as a predictive biomarker of radiotherapy resistance

PURPOSE

Hypoxia is a hallmark of solid tumors that is related to radiotherapy resistance. As galectin members, such as galectin-1 and galectin-3, are associated with tumor hypoxia, herein we aimed to investigate whether positron emission tomography (PET) imaging of galectin expression can be employed to effectively pinpoint tumor hypoxia, and to predict radiotherapy resistance.

METHODS

We synthesized a galectin-targeting radiotracer, designated ⁶⁸Ga-galectracer, by radiolabeling a thiodigalactoside derivative. The properties of ⁶⁸Ga-galectracer for PET imaging of tumor hypoxia were characterized in three tumor hypoxia mouse models. Additionally, preliminary PET/CT was performed in two patients with lung cancer to investigate the potential application of ⁶⁸Ga-galectracer for clinical imaging.

RESULTS

High-contrast imaging was achieved in the murine acute hypoxia tumor model, A549 natural hypoxia model, and sorafenib treatment-induced hypoxic 4T1 tumor model by PET using ⁶⁸Ga-galectracer. In fact, ⁶⁸Ga-galectracer exhibited superior hypoxia detection to that of ¹⁸F-misonidazole in the 4T1 tumors. Moreover, tumors with high galectin expression levels, as detected by ⁶⁸Ga-galectracer PET, exhibited significantly lower responses to subsequent radiotherapy compared to those with low galectin expression levels. In patients with lung cancer, PET imaging using ⁶⁸Ga-galectracer provided data that were complementary to that of the glucose metabolic PET radiotracer ¹⁸F-fluorodeoxyglucose.

CONCLUSION

⁶⁸Ga-galectracer is a promising radiotracer for PET-based imaging of tumor hypoxia in vivo. Thus, hypoxia PET with ⁶⁸Ga-galectracer could provide a noninvasive approach to proactively predict radiotherapy efficacy.

TRIAL REGISTRATION

Chictr.org.cn (ChiCTR2000029522). Registered 03 February 2020.

Host T cell dedifferentiation effects drive HIV-1 latency stability

The development of therapies to eliminate the latent HIV-1 reservoir is hampered by our incomplete understanding of the biomolecular mechanism governing HIV-1 latency. To further complicate matters, recent single cell RNA-seq studies reported extensive heterogeneity between latently HIV-1-infected primary T cells, implying that latent HIV-1 infection can persist in greatly differing host cell environments. We here show that transcriptomic heterogeneity is also found between latently infected T cell lines, which allowed us to study the underlying mechanisms of intercell heterogeneity at high signal resolution. Latently infected T cells exhibited a de-differentiated phenotype, characterized by the loss of T cell-specific markers and gene regulation profiles reminiscent of hematopoietic stem cells (HSC). These changes had functional consequences. As reported for stem cells, latently HIV-1 infected T cells efficiently forced lentiviral superinfections into a latent state and favored glycolysis. As a result, metabolic reprogramming or cell re-differentiation destabilized latent infection. Guided by these findings, data-mining of single cell RNA-seq data of latently HIV-1 infected primary T cells from patients revealed the presence of similar dedifferentiation motifs. >20% of the highly detectable genes that were differentially regulated in latently infected cells were associated with hematopoietic lineage development (e.g. HUWE1, IRF4, PRDM1, BATF3, TOX, ID2, IKZF3, CDK6) or were hematopoietic markers (SRGN; hematopoietic proteoglycan core protein). The data add to evidence that the biomolecular phenotype of latently HIV-1 infected cells differs from normal T cells and strategies to address their differential phenotype need to be considered in the design of therapeutic cure interventions. IMPORTANCE HIV-1 persists in a latent reservoir in memory CD4 T cells for the lifetime of a patient. Understanding the biomolecular mechanisms used by the host cells to suppress viral expression will provide essential insights required to develop curative therapeutic interventions. Unfortunately, our current understanding of these control mechanisms is still limited. By studying gene expression profiles, we demonstrated that latently HIV-1-infected T cells have a de-differentiated T cell phenotype. Software-based data integration allowed for the identification of drug targets that would re-differentiate viral host cells and, in extension, destabilize latent HIV-1 infection events. The importance of the presented data lies within the clear demonstration that HIV-1 latency is a host cell phenomenon. As such, therapeutic strategies must first restore proper host cell functionality to accomplish efficient HIV-1 reactivation.

Galectins as regulators of cell survival in the leukemia niche

The microenvironment within the bone marrow (BM) contains support cells that promote leukemia cell survival and suppress host anti-tumor defenses. Galectins are a family of beta-galactoside binding proteins that are critical components in the tumor microenvironment. Galectin 1 (LGALS1) and Galectin 3 (LGALS3) as regulators of RAS signaling intracellularly and as inhibitors of immune cells extracellularly are perhaps the best studied members for their role in leukemia biology. Interest in Galectin 9 (LGALS9) is growing as this galectin has been identified as an immune checkpoint molecule. LGALS9 also supports leukemia stem cells (LSCs) though a mechanism of action is not clear. LGALS1 and LGALS3 each participate in a diverse number of survival pathways that promote drug resistance by supporting pro-tumor molecules such BCL2, MCL-1, and MYC and blocking tumor suppressors like p53. Acute myeloid leukemia (AML) BM mesenchymal stromal cells (MSC) have protein signatures that differ from healthy donor MSC. Elevated LGALS3 protein in AML MSC is associated with refractory disease/relapse demonstrating that MSC derived galectin impacts patient survival. LGALS3 is a critical determining factor whether MSC differentiate into adipocytes or osteoblasts so the galectin influences the cellular composition of the leukemia niche. Both LGALS3 and LGALS1 when secreted can suppress immune function. Both galectins can induce apoptosis of T cells. LGALS3 also modulates T cell receptor endocytosis and impairs interferon mediated chemokine production by binding glycosylated interferon. LGALS3 as a TIM3 binding partner acts to suppress T cell function. Galectins also impact leukemia cell mobilization and may participate in homing mechanisms. LGALS3 participates in transport mechanism of integrins, receptors, and other molecules that control cell adhesion and cell:cell interactions. The diversity of these various functions demonstrate the importance of these galectins in the leukemia niche. This review will cover the role of LGALS1, LGALS3, and LGALS9 in the various processes that are critical for maintaining leukemia cells in the tumor microenvironment.

Galectin 3 expression in regional lymph nodes and lymph node metastases of oral squamous cell carcinomas

BACKGROUND

Neck dissection is standard in surgical management of oral squamous cell carcinomas (oscc). However, the immunologic link between primary tumor and lymph nodes is insufficiently understood. Galectin 3 (Gal3) promotes M2 polarization of macrophages and contributes to immunosuppression. The current study analyzes the association between Gal3 expression in regional lymph nodes of oscc with histomorphologic parameters (T-, N-, L- Pn-stage, grading) of the primary tumor. Additionally, Gal3 expression is correlated with markers of macrophage polarization (M1 vs. M2).

METHODS

Preoperative diagnostic biopsies (n = 26), tumor resection specimens (n = 34), tumor-free lymph nodes (n = 28) and lymph node metastases (n = 10) of T1/T2 oscc patients were immunohistochemically analyzed for Gal3 and macrophage marker (CD68, CD11c, CD163 and MRC1) expression. The number of positive cells and the expression ratios were quantitatively assessed.

RESULTS

High Gal3 expression in tumor-free regional lymph nodes was significantly (p < 0.05) associated with increased tumor size. The epithelial compartment of lymph node metastases showed a significantly (p < 0.05) increased Gal3 expression compared to biopsies and tumor resection specimens. Cell density of M2 macrophages was significantly (p < 0.05) and positively correlated with the number of Gal3 expressing cells in lymph nodes and tumor specimens.

CONCLUSION

Gal3 expression in regional lymph nodes might be associated with oscc progression. The increased Gal3 expression in regional lymph nodes of larger tumors underlines the need of immunomodulatory treatment concepts in early-stage oscc. Blocking of Gal3 might be a therapeutic option in oral cancer.

Increased Reactive Oxygen Species and Cell Cycle Defects Contribute to Anemia in the RASA3 Mutant Mouse Model scat

RASA3 is a Ras GTPase activating protein that plays a critical role in blood formation. The autosomal recessive mouse model scat (severe combined anemia and thrombocytopenia) carries a missense mutation in Rasa3. Homozygotes present with a phenotype characteristic of bone marrow failure that is accompanied by alternating episodes of crisis and remission. The mechanism leading to impaired erythropoiesis and peripheral cell destruction as evidenced by membrane fragmentation in scat is unclear, although we previously reported that the mislocalization of RASA3 to the cytosol of reticulocytes and mature red cells plays a role in the disease. In this study, we further characterized the bone marrow failure in scat and found that RASA3 plays a central role in cell cycle progression and maintenance of reactive oxygen species (ROS) levels during terminal erythroid differentiation, without inducing apoptosis of the precursors. In scat mice undergoing crises, there is a consistent pattern of an increased proportion of cells in the G₀/G₁ phase at the basophilic and polychromatophilic stages of erythroid differentiation, suggesting that RASA3 is involved in the G₁ checkpoint. However, this increase in G₁ is transient, and either resolves or becomes indiscernible by the orthochromatic stage. In addition, while ROS levels are normal early in erythropoiesis, there is accumulation of superoxide levels at the reticulocyte stage (DHE increased 40% in scat; p = 0.02) even though mitochondria, a potential source for ROS, are eliminated normally. Surprisingly, apoptosis is significantly decreased in the scat bone marrow at the proerythroblastic (15.3%; p = 0.004), polychromatophilic (8.5%; p = 0.01), and orthochromatic (4.2%; p = 0.02) stages. Together, these data indicate that ROS accumulation at the reticulocyte stage, without apoptosis, contributes to the membrane fragmentation observed in scat. Finally, the cell cycle defect and increased levels of ROS suggest that scat is a model of bone marrow failure with characteristics of aplastic anemia.

Ablation of the mammalian lectin galectin-8 induces bone defects in mice

Mice overexpressing galectin-8 [gal-8 transgenic (Tg)], a secreted mammalian lectin, exhibit enhanced bone turnover and reduced bone mass, similar to cases of postmenopausal osteoporosis. Here, we show that gal-8 knockout (KO) mice have increased bone mass accrual at a young age but exhibit accelerated bone loss during adulthood. These phenotypes can be attributed to a gal-8-mediated increase in receptor activator of NF-κB ligand (RANKL) expression that promotes osteoclastogenesis, combined with direct inhibition of osteoblast differentiation, evident by reduced bone morphogenetic protein (BMP) signaling, reduced phosphorylation of receptor regulated mothers against decapentaplegic homolog (R-SMAD) and reduced expression of osteoblast differentiation markers osterix, osteocalcin, runt-related transcription factor 2 (RUNX2), dentin matrix acidic phosphoprotein-1 (DMP1), and alkaline phosphatase. At the same time, gal-8 promotes expression of estrogen receptor α (ESR1). Accordingly, the rate of bone loss is accelerated in ovariectomized, estrogen-deficient gal-8 Tg mice, whereas gal-8 KO mice, having low levels of ESR1, are refractory to ovariectomy. Finally, gal-8 mRNA positively correlates with the mRNA levels of osteoclastogenic markers RANKL, tartrate-resistant acid phosphatase, and cathepsin K in human femurs. Collectively, these findings identify gal-8 as a new physiologic player in the regulation of bone mass.-Vinik, Y., Shatz-Azoulay, H., Hiram-Bab, S., Kandel, L., Gabet, Y., Rivkin, G., Zick, Y. Ablation of the mammalian lectin galectin-8 induces bone defects in mice.

Role of Galectins in Multiple Myeloma

Galectins are a family of lectins that bind β-galactose-containing glycoconjugates and are characterized by carbohydrate-recognition domains (CRDs). Galectins exploit several biological functions, including angiogenesis, regulation of immune cell activities and cell adhesion, in both physiological and pathological processes, as tumor progression. Multiple myeloma (MM) is a plasma cell (PC) malignancy characterized by the tight adhesion between tumoral PCs and bone marrow (BM) microenvironment, leading to the increase of PC survival and drug resistance, MM-induced neo-angiogenesis, immunosuppression and osteolytic bone lesions. In this review, we explore the expression profiles and the roles of galectin-1, galectin-3, galectin-8 and galectin-9 in the pathophysiology of MM. We focus on the role of these lectins in the interplay between MM and BM microenvironment cells showing their involvement in MM progression mainly through the regulation of PC survival and MM-induced angiogenesis and osteoclastogenesis. The translational impact of these pre-clinical pieces of evidence is supported by recent data that indicate galectins could be new attractive targets to block MM cell growth in vivo and by the evidence that the expression levels of LGALS1 and LGALS8, genes encoding for galectin-1 and galectin-8 respectively, correlate to MM patients’ survival.

Galectin-1 promotes an M2 macrophage response to polydioxanone scaffolds

Regulating soft tissue repair to prevent fibrosis and promote regeneration is central to creating a microenvironment conducive to soft tissue development. Macrophages play an important role in this process. The macrophage response can be modulated using biomaterials, altering cytokine and growth factor secretion to promote regeneration. Electrospun polydioxanone (PDO) fiber scaffolds promoted an M2 phenotype when macrophages were cultured on large diameter, highly porous scaffolds, but an M1 phenotype on smaller diameter fibers. In this study, we investigated whether incorporation of galectin-1, an immunosuppressive protein that enhances muscle regeneration, could promote the M2 response. Galectin-1 was incorporated into large and small fiber PDO scaffolds during electrospinning. Galectin-1 incorporation increased arginase-1 and reduced iNOS and IL-6 production in mouse bone-marrow derived macrophages compared with PDO alone for both scaffold types. Inhibition of ERK mitogen-activated protein kinase did not alter galectin-1 effects on arginase-1 and iNOS expression, but reversed IL-6 suppression, indicating that IL-6 is mediated by a different mechanism. Our results suggest that galectin-1 can be used to modulate macrophage commitment to a pro-regenerative M2 phenotype, which may positively impact tissue regeneration when using small diameter PDO scaffolds. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2562-2571, 2017.

Serum galectin-1 in patients with multiple myeloma: associations with survival, angiogenesis, and biomarkers of macrophage activation

Galectin-1 (Gal-1) is known to regulate cell signaling within the immune system and may be a target for new anticancer immune therapy. In patients with chronic lymphocytic leukemia (CLL) and classical Hodgkin lymphoma (cHL), high levels of Gal-1 within the tumor microenvironment were associated with worse disease state or poor outcome. Gal-1 can be secreted from cells by an unknown mechanism, and levels in blood samples were associated with high tumor burden and worse disease state in cHL and CLL patients. However, serum levels of Gal-1 have never been investigated in patients with multiple myeloma (MM). We measured serum Gal-1 levels in samples from patients with treatment demanding MM at the time of diagnosis (n=102) and after treatment (n=24) and examined associations of serum Gal-1 with clinicopathological information obtained from patient medical records, as well as data on bone marrow angiogenesis and the macrophage activation biomarkers soluble CD163 (sCD163) and soluble mannose receptor. Serum Gal-1 levels were not elevated in patients with MM at diagnosis compared with healthy donors (median values 8.48 vs 11.93 ng/mL, P=0.05), which is in contrast to results in cHL and CLL. Furthermore, Gal-1 levels did not show association with bone marrow angiogenesis, clinicopathological parameters, overall survival, or response to treatment. There was a statically significant association between Gal-1 and sCD163 levels (R=0.24, P=0.02), but not with soluble mannose receptor (P=0.92). In conclusion, our results indicate that Gal-1 is not an important serum biomarker in MM, which is in contrast to data from patients with cHL and CLL. However, the association with sCD163 is in line with previous data showing that Gal-1 may be involved in alternative (M2-like) activation of macrophages.

The mammalian lectin galectin-8 induces RANKL expression, osteoclastogenesis, and bone mass reduction in mice

Skeletal integrity is maintained by the co-ordinated activity of osteoblasts, the bone-forming cells, and osteoclasts, the bone-resorbing cells. In this study, we show that mice overexpressing galectin-8, a secreted mammalian lectin of the galectins family, exhibit accelerated osteoclasts activity and bone turnover, which culminates in reduced bone mass, similar to cases of postmenopausal osteoporosis and cancerous osteolysis. This phenotype can be attributed to a direct action of galectin-8 on primary cultures of osteoblasts that secrete the osteoclastogenic factor RANKL upon binding of galectin-8. This results in enhanced differentiation into osteoclasts of the bone marrow cells co-cultured with galectin-8-treated osteoblasts. Secretion of RANKL by galectin-8-treated osteoblasts can be attributed to binding of galectin-8 to receptor complexes that positively (uPAR and MRC2) and negatively (LRP1) regulate galectin-8 function. Our findings identify galectins as new players in osteoclastogenesis and bone remodeling, and highlight a potential regulation of bone mass by animal lectins.

DOI:http://dx.doi.org/10.7554/eLife.05914.001

The forces applied to the body during daily activities cause bones to be constantly remodeled, which is essential for keeping them healthy. In most adult organisms, new bone is created at the same rate at which old bone is destroyed. This means that overall bone mass remains the same. But, in diseases such as osteoporosis or bone cancer, bone is destroyed more rapidly than at which new bone is made. This leads to brittle bones that are more likely to fracture. Understanding how to increase the rate of bone renewal might therefore help scientists develop new treatments for bone diseases.

Bone is created by cells called osteoblasts and destroyed by other cells called osteoclasts. Both of these types of cells develop from stem cells in the bone marrow. The activity of these cells is controlled by a number of factors, including the matrix of proteins that holds bone together. A group of proteins called galectins are known to act as a bridge between some of the matrix proteins and molecules on the surface of the cells.

Vinik et al. took osteoblasts from a mouse skull, grew them in the laboratory, and then exposed them to a galectin protein called galectin-8. This made the osteoblasts release a protein called RANKL, which is known to boost osteoclast activity. When osteoblasts that had been exposed to galectin-8 were grown alongside bone marrow stem cells, more of the stem cells developed into the bone-destroying osteoclasts.

Mice that were genetically engineered to produce more galectin-8 than normal mice develop brittle bones, despite also creating new bone at a higher rate than do normal mice. This is because osteoclast activity increases at a greater rate, resulting in an overall loss of bone in these animals. This is similar to what occurs in some individuals with osteoporosis. These experiments therefore suggest that galectin-8 plays an important role in bone remodeling and that it may be a potential target for drugs that treat diseases that weaken bones.

DOI:http://dx.doi.org/10.7554/eLife.05914.002

Galectins in hematological malignancies

PURPOSE OF REVIEW

Galectins are a family of lectin molecules that have emerged as key players in inflammation and tumor progresssion by displaying intracellular and extracellular activities. This review describes the recent advances on the role of galectins in hematological neoplasms.

RECENT FINDINGS

Galectin-1 and galectin-3 are the best studied galectins in oncohematology. Increased expression of galectin-1 has been associated with tumor progression in Hodgkin's lymphoma and chronic lymphocytic leukemia, whereas galectin-3 plays a supporting role in chronic myelogenous leukemia and multiple myeloma. Functional studies have assigned a key role for galectin-1 as a negative regulator of T-cell immunity in Hodgkin's lymphoma and cutaneous T-cell lymphoma. Of therapeutic interest is the development of agents with the capacity to interfere with galectin functions.

SUMMARY

Current knowledge indicates a key role for galectins in hematological neoplasms by favoring the growth and survival of tumor cells and facilitating tumor immune escape. Intervention using specific galectin inhibitors is emerging as an attractive therapeutic option to alter the course of these malignancies.

Leveraging fluorinated glucosamine action to boost antitumor immunity

N-acetyllactosaminyl glycans are key regulators of the vitality and effector function of antitumor T cells. When galectin-1 (Gal-1) binds N-acetyllactosamines on select membrane glycoproteins on antitumor T cells, these cells either undergo apoptosis or become immunoregulatory. Methods designed to antagonize expression or function of these N-acetyllactosamines on N-glycans and O-glycans have thus intensified. Since tumors can produce an abundance of Gal-1, Gal-1 is considered a critical factor for protecting tumor cells from T cell-mediated antitumor activity. Recent efforts have capitalized on the anti-N-acetyllactosamine action of fluorinated glucosamines to treat antitumor T cells, resulting in diminished Gal-1-binding and higher antitumor T cell levels. In this perspective, the prospect of fluorinated glucosamines in eliminating N-acetyllactosamines on antitumor T cells to boost antitumor immunity is presented.

Protective effect of Phellinus linteus polysaccharide extracts against thioacetamide-induced liver fibrosis in rats: a proteomics analysis

Background

The hepatoprotective potential of Phellinus linteus polysaccharide (PLP) extracts has been described. However, the molecular mechanism of PLP for the inhibition of liver fibrosis is unclear. This study aims to investigate the molecular protein signatures involved in the hepatoprotective mechanisms of PLP via a proteomics approach using a thioacetamide (TAA)-induced liver fibrosis rat model.

Methods

Male Sprague–Dawley rats were divided into three groups of six as follows: Normal group; TAA group, in which rats received TAA only; and PLP group, in which rats received PLP and TAA. Liver fibrosis was induced in the rats by repeated intraperitoneal injections of TAA at a dose of 200 mg/kg body weight twice a week for 4 weeks. PLP was given orally at a dose of 50 mg/kg body weight twice a day from the beginning of the TAA treatment until the end of the experiment. The development of liver cirrhosis was verified by histological examination. Liver proteomes were established by two-dimensional gel electrophoresis. Proteins with significantly altered expression levels were identified by matrix-assisted laser desorption/ionization-time of flight/time of flight mass spectrometry and the differentially expressed proteins were validated by immunohistochemical staining and reverse transcription polymerase chain reaction.

Results

Histological staining showed a remarkable reduction in liver fibrosis in the rats with PLP treatment. A total of 13 differentially expressed proteins including actin, tubulin alpha-1C chain, preprohaptoglobin, hemopexin, galectin-5, glutathione S-transferase alpha-4 (GSTA4), branched chain keto acid dehydrogenase hterotetrameric E1 subunit alpha (BCKDHA), glutathione S-transferase mu (GSTmu); glyceraldehyde-3-phosphate dehydrogenase (GAPDH); thiosulfate sulfurtransferase (TFT); betaine-homocysteine S-methyltransferase 1 (BHMT1); quinoid dihydropteridine reductase (QDPR); ribonuclease UK114 were observed between the TAA and PLP groups. These proteins are involved in oxidative stress, heme and iron metabolism, cysteine metabolism, and branched-chain amino acid catabolism.

Conclusion

The proteomics data indicate that P. linteus may be protective against TAA-induced liver fibrosis via regulation of oxidative stress pathways, heat shock pathways, and metabolic pathways for amino acids and nucleic acids.