LRP1: A chameleon receptor of lung inflammation and repair

Cerebral amyloid angiopathy and the immune system

Cerebral amyloid angiopathy (CAA) is characterized by the accumulation of amyloid protein in the walls of cerebral blood vessels. This deposition of amyloid causes damage to the cerebral vasculature, resulting in blood-brain barrier disruption, cerebral hemorrhage, cognitive decline, and dementia. The role of the immune system in CAA is complex and not fully understood. While the immune system has a clear role in the rare inflammatory variants of CAA (CAA related inflammation and Abeta related angiitis), the more common variants of CAA also have immune system involvement. In a protective role, immune cells may facilitate the clearance of beta-amyloid from the cerebral vasculature. The immune system can also contribute to CAA pathology, promoting vascular injury, blood-brain barrier breakdown, inflammation, and progression of CAA. In this review, we summarize the role of the immune system in CAA, including the potential of immune based treatment strategies to slow vascular disease in CAA and associated cognitive impairment, white matter disease progression, and reduce the risk of cerebral hemorrhage. HIGHLIGHTS: The immune system has a role in cerebral amyloid angiopathy (CAA) which is summarized in this review. There is an inflammatory response to beta-amyloid that may contribute to brain injury and cognitive impairment. Immune cells may facilitate the clearance of beta-amyloid from the cerebral vasculature. Improved understanding of the immune system in CAA may afford novel treatment to improve outcomes in patients with CAA.

Novel insights into the multifaceted and tissue-specific roles of the endocytic receptor LRP1

Receptor-mediated endocytosis provides a mechanism for the selective uptake of specific molecules thereby controlling the composition of the extracellular environment and biological processes. The low-density lipoprotein receptor-related protein 1 (LRP1) is a widely expressed endocytic receptor that regulates cellular events by modulating the levels of numerous extracellular molecules via rapid endocytic removal. LRP1 also participates in signalling pathways through this modulation as well as in the interaction with membrane receptors and cytoplasmic adaptor proteins. LRP1 single nucleotide polymorphisms are associated with several diseases and conditions such as migraines, aortic aneurysms, cardiopulmonary dysfunction, corneal clouding, and bone dysmorphology and mineral density. Studies using Lrp1 knockout mice revealed a critical, non-redundant and tissue-specific role of LRP1 in regulating various physiological events. However, exactly how LRP1 functions to regulate so many distinct and specific processes is still not fully clear. Our recent proteomics studies have identified more than 300 secreted proteins that either directly interact with LRP1 or are modulated by LRP1 in various tissues. This review will highlight the remarkable ability of this receptor to regulate secreted molecules in a tissue-specific manner and discuss potential mechanisms underpinning such specificity. Uncovering the depth of these "hidden" specific interactions modulated by LRP1 will provide novel insights into a dynamic and complex extracellular environment that is involved in diverse biological and pathological processes.

Astrocytic LRP1 enables mitochondria transfer to neurons and mitigates brain ischemic stroke by suppressing ARF1 lactylation

Low-density lipoprotein receptor-related protein-1 (LRP1) is an endocytic/signaling cell-surface receptor that regulates diverse cellular functions, including cell survival, differentiation, and proliferation. LRP1 has been previously implicated in the pathogenesis of neurodegenerative disorders, but there are inconsistencies in its functions. Therefore, whether and how LRP1 maintains brain homeostasis remains to be clarified. Here, we report that astrocytic LRP1 promotes astrocyte-to-neuron mitochondria transfer by reducing lactate production and ADP-ribosylation factor 1 (ARF1) lactylation. In astrocytes, LRP1 suppressed glucose uptake, glycolysis, and lactate production, leading to reduced lactylation of ARF1. Suppression of astrocytic LRP1 reduced mitochondria transfer into damaged neurons and worsened ischemia-reperfusion injury in a mouse model of ischemic stroke. Furthermore, we examined lactate levels in human patients with stroke. Cerebrospinal fluid (CSF) lactate was elevated in stroke patients and inversely correlated with astrocytic mitochondria. These findings reveal a protective role of LRP1 in brain ischemic stroke by enabling mitochondria-mediated astrocyte-neuron crosstalk.

ADAMTS4 is a crucial proteolytic enzyme for versican cleavage in the amnion at parturition

Hyalectan cleavage may play an important role in extracellular matrix remodeling. However, the proteolytic enzyme responsible for hyalectan degradation for fetal membrane rupture at parturition remains unknown. Here, we reveal that versican (VCAN) is the major hyalectan in the amnion, where its cleavage increases at parturition with spontaneous rupture of membrane. We further reveal that ADAMTS4 is a crucial proteolytic enzyme for VCAN cleavage in the amnion. Inflammatory factors may enhance VCAN cleavage by inducing ADAMTS4 expression and inhibiting ADAMTS4 endocytosis in amnion fibroblasts. In turn, versikine, the VCAN cleavage product, induces inflammatory factors in amnion fibroblasts, thereby forming a feedforward loop between inflammation and VCAN degradation. Mouse studies show that intra-amniotic injection of ADAMTS4 induces preterm birth along with increased VCAN degradation and proinflammatory factors abundance in the fetal membranes. Conclusively, there is enhanced VCAN cleavage by ADAMTS4 in the amnion at parturition, which can be reenforced by inflammation.

Immune Checkpoint and Other Receptor-Ligand Pairs Modulating Macrophages in Cancer: Present and Prospects

Immunotherapy, especially immune checkpoint blocking, has become the primary anti-tumor treatment in recent years. However, the current immune checkpoint inhibitor (ICI) therapy is far from satisfactory. Macrophages are a key component of anti-tumor immunity as they are a common immune cell subset in tumor tissues and act as a link between innate and adaptive immunity. Hence, understanding the regulation of macrophage activation in tumor tissues by receptor-ligand interaction will provide promising macrophage-targeting strategies to complement current adaptive immunity-based immunotherapy and traditional anti-tumor treatment. This review aims to offer a systematic summary of the current advances in number, structure, expression, biological function, and interplay of immune checkpoint and other receptor-ligand between macrophages and tumor cells.

Untangling the Extracellular Matrix of Idiopathic Epiretinal Membrane: A Path Winding among Structure, Interactomics and Translational Medicine

Idiopathic epiretinal membranes (iERMs) are fibrocellular sheets of tissue that develop at the vitreoretinal interface. The iERMs consist of cells and an extracellular matrix (ECM) formed by a complex array of structural proteins and a large number of proteins that regulate cell–matrix interaction, matrix deposition and remodelling. Many components of the ECM tend to produce a layered pattern that can influence the tractional properties of the membranes. We applied a bioinformatics approach on a list of proteins previously identified with an MS-based proteomic analysis on samples of iERM to report the interactome of some key proteins. The performed pathway analysis highlights interactions occurring among ECM molecules, their cell receptors and intra- or extracellular proteins that may play a role in matrix biology in this special context. In particular, integrin β1, cathepsin B, epidermal growth factor receptor, protein-glutamine gamma-glutamyltransferase 2 and prolow-density lipoprotein receptor-related protein 1 are key hubs in the outlined protein–protein cross-talks. A section on the biomarkers that can be found in the vitreous humor of patients affected by iERM and that can modulate matrix deposition is also presented. Finally, translational medicine in iERM treatment has been summed up taking stock of the techniques that have been proposed for pharmacologic vitreolysis.

Extracellular HMGB1 Impairs Macrophage-Mediated Efferocytosis by Suppressing the Rab43-Controlled Cell Surface Transport of CD91

High-mobility group box 1 (HMGB1) protein can impair phagocyte function by suppressing the macrophage-mediated clearance of apoptotic cells (ACs), thereby delaying inflammation resolution in the lungs and allowing the progression of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, the precise mechanism underlying this HMGB1-mediated inhibition of efferocytosis remains unknown. The aim of this study was to determine the effect of HMGB1 on macrophage-mediated efferocytosis. We discovered that HMGB1 prevented efferocytosis by bone marrow-derived macrophages (BMDMs) and suppressed the expression of Ras-related GTP-binding protein 43 (Rab43), a member of the Ras-associated binding (Rab) family. The downregulation of Rab43 expression resulted in impaired clearance of apoptotic thymocytes by BMDMs. Subsequent analysis of HMGB1-treated and Rab43-deficient BMDMs revealed the inhibited transport of cluster of differentiation 91 (CD91), a phagocyte recognition receptor, from the cytoplasm to the cell surface. Notably, Rab43 directly interacted with CD91 to mediate its intercellular trafficking. Furthermore, Rab43 knockout delayed the inflammation resolution and aggravated the lung tissue damage in mice with ALI. Therefore, our results provide evidence that HMGB1 impairs macrophage-mediated efferocytosis and delays inflammation resolution by suppressing the Rab43-regulated anterograde transport of CD91, suggesting that the restoration of Rab43 levels is a promising strategy for attenuating ALI and ARDS in humans.

LRP1 loss in airway epithelium exacerbates smoke-induced oxidative damage and airway remodeling

The LDL receptor-related protein 1 (LRP1) partakes in metabolic and signaling events regulated in a tissue-specific manner. The function of LRP1 in airways has not been studied. We aimed to study the function of LRP1 in smoke-induced disease. We found that bronchial epithelium of patients with chronic obstructive pulmonary disease and airway epithelium of mice exposed to smoke had increased LRP1 expression. We then knocked out LRP1 in human bronchial epithelial cells in vitro and in airway epithelial club cells in mice. In vitro, LRP1 knockdown decreased cell migration and increased transforming growth factor β activation. Tamoxifen-inducible airway-specific LRP1 knockout mice (club Lrp1-/-) induced after complete lung development had increased inflammation in the bronchoalveolar space and lung parenchyma at baseline. After 6 months of smoke exposure, club Lrp1-/- mice showed a combined restrictive and obstructive phenotype, with lower compliance, inspiratory capacity, and forced expiratory volume0.05/forced vital capacity than WT smoke-exposed mice. This was associated with increased values of Ashcroft fibrotic index. Proteomic analysis of room air exposed-club Lrp1-/- mice showed significantly decreased levels of proteins involved in cytoskeleton signaling and xenobiotic detoxification as well as decreased levels of glutathione. The proteome fingerprint created by smoke eclipsed many of the original differences, but club Lrp1-/- mice continued to have decreased lung glutathione levels and increased protein oxidative damage and airway cell proliferation. Therefore, LRP1 deficiency leads to greater lung inflammation and damage and exacerbates smoke-induced lung disease.

Interplay of Low-Density Lipoprotein Receptors, LRPs, and Lipoproteins in Pulmonary Hypertension

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LDLR regulates oxidized LDL level, which is increased in lung and blood from PAH patients.

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LRP1 preserving vascular homeostasis is decreased in PAH patients.

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LRP5/6 regulating Wnt signaling is upregulated in PH.

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The LRP8 (aka ApoER2) ligand ApoE protects from PAH.

The low-density lipoprotein receptor (LDLR) gene family includes LDLR, very LDLR, and LDL receptor–related proteins (LRPs) such as LRP1, LRP1b (aka LRP-DIT), LRP2 (aka megalin), LRP4, and LRP5/6, and LRP8 (aka ApoER2). LDLR family members constitute a class of closely related multifunctional, transmembrane receptors, with diverse functions, from embryonic development to cancer, lipid metabolism, and cardiovascular homeostasis. While LDLR family members have been studied extensively in the systemic circulation in the context of atherosclerosis, their roles in pulmonary arterial hypertension (PAH) are understudied and largely unknown. Endothelial dysfunction, tissue infiltration of monocytes, and proliferation of pulmonary artery smooth muscle cells are hallmarks of PAH, leading to vascular remodeling, obliteration, increased pulmonary vascular resistance, heart failure, and death. LDLR family members are entangled with the aforementioned detrimental processes by controlling many pathways that are dysregulated in PAH; these include lipid metabolism and oxidation, but also platelet-derived growth factor, transforming growth factor β1, Wnt, apolipoprotein E, bone morpohogenetic proteins, and peroxisome proliferator-activated receptor gamma. In this paper, we discuss the current knowledge on LDLR family members in PAH. We also review mechanisms and drugs discovered in biological contexts and diseases other than PAH that are likely very relevant in the hypertensive pulmonary vasculature and the future care of patients with PAH or other chronic, progressive, debilitating cardiovascular diseases.

Role of the LRP1-pPyk2-MMP9 pathway in hyperoxia-induced lung injury in neonatal rats

OBJECTIVES

To study the role of the low-density lipoprotein receptor-related protein 1 (LRP1)-proline-rich tyrosine kinase 2 phosphorylation (pPyk2)-matrix metalloproteinases 9 (MMP9) pathway in hyperoxia-induced lung injury in neonatal rats.

METHODS

A total of 16 neonatal rats were randomly placed in chambers containing room air (air group) or 95% medical oxygen (hyperoxia group) immediately after birth, with 8 rats in each group. All of the rats were sacrificed on day 8 of life. Hematoxylin and eosin staining was used to observe the pathological changes of lung tissue. ELISA was used to measure the levels of soluble LRP1 (sLRP1) and MMP9 in serum and bronchoalveolar lavage fluid (BALF). Western blot was used to measure the protein expression levels of LRP1, MMP9, Pyk2, and pPyk2 in lung tissue. RT-PCR was used to measure the mRNA expression levels of LRP1 and MMP9 in lung tissue.

RESULTS

The hyperoxia group had significantly higher levels of sLRP1 and MMP9 in serum and BALF than the air group (P<0.05). Compared with the air group, the hyperoxia group had significant increases in the protein expression levels of LRP1, MMP9, and pPyk2 in lung tissue (P<0.05). The hyperoxia group had significantly higher relative mRNA expression levels of LRP1 and MMP9 in lung tissue than the air group (P<0.05).

CONCLUSIONS

The activation of the LRP1-pPyk2-MMP9 pathway is enhanced in hyperoxia-induced lung injury in neonatal rats, which may be involved in the pathogenesis of bronchopulmonary dysplasia.

Plasma Membrane Receptors Involved in the Binding and Response of Osteoclasts to Noncellular Components of the Bone

Osteoclasts differentiate from hematopoietic cells and resorb the bone in response to various signals, some of which are received directly from noncellular elements of the bone. In vitro, adherence to the bone triggers the reduction of cell–cell fusion events between osteoclasts and the activation of osteoclasts to form unusual dynamic cytoskeletal and membrane structures that are required for degrading the bone. Integrins on the surface of osteoclasts are known to receive regulatory signals from the bone matrix. Regulation of the availability of these signals is accomplished by enzymatic alterations of the bone matrix by protease activity and phosphorylation/dephosphorylation events. Other membrane receptors are present in osteoclasts and may interact with as yet unidentified signals in the bone. Bone mineral has been shown to have regulatory effects on osteoclasts, and osteoclast activity is also directly modulated by mechanical stress. As understanding of how osteoclasts and other bone cells interact with the bone has emerged, increasingly sophisticated efforts have been made to create bone biomimetics that reproduce both the structural properties of the bone and the bone’s ability to regulate osteoclasts and other bone cells. A more complete understanding of the interactions between osteoclasts and the bone may lead to new strategies for the treatment of bone diseases and the production of bone biomimetics to repair defects.

Resolution of inflammation in bone regeneration: From understandings to therapeutic applications

Impaired bone healing occurs in 5-10% of cases following injury, leading to a significant economic and clinical impact. While an inflammatory response upon injury is necessary to facilitate healing, its resolution is critical for bone tissue repair as elevated acute or chronic inflammation is associated with impaired healing in patients and animal models. This process is governed by important crosstalk between immune cells through mediators that contribute to resolution of inflammation in the local healing environment. Approaches modulating the initial inflammatory phase followed by its resolution leads to a pro-regenerative environment for bone regeneration. In this review, we discuss the role of inflammation in bone repair, the negative impact of dysregulated inflammation on bone tissue regeneration, and how timely resolution of inflammation is necessary to achieve normal healing. We will discuss applications of biomaterials to treat large bone defects with a specific focus on resolution of inflammation to modulate the immune environment following bone injury, and their observed functional benefits. We conclude the review by discussing future strategies that could lead to the realization of anti-inflammatory therapeutics for bone tissue repair.

The Dual Role of Low-Density Lipoprotein Receptor-Related Protein 1 in Atherosclerosis

Low-density lipoprotein receptor–related protein-1 (LRP1) is a large endocytic and signaling receptor belonging to the LDL receptor (LDLR) gene family and that is widely expressed in several tissues. LRP1 comprises a large extracellular domain (ECD; 515 kDa, α chain) and a small intracellular domain (ICD; 85 kDa, β chain). The deletion of LRP1 leads to embryonic lethality in mice, revealing a crucial but yet undefined role in embryogenesis and development. LRP1 has been postulated to participate in numerous diverse physiological and pathological processes ranging from plasma lipoprotein homeostasis, atherosclerosis, tumor evolution, and fibrinolysis to neuronal regeneration and survival. Many studies using cultured cells and in vivo animal models have revealed the important roles of LRP1 in vascular remodeling, foam cell biology, inflammation and atherosclerosis. However, its role in atherosclerosis remains controversial. LRP1 not only participates in the removal of atherogenic lipoproteins and proatherogenic ligands in the liver but also mediates the uptake of aggregated LDL to promote the formation of macrophage- and vascular smooth muscle cell (VSMC)-derived foam cells, which causes a prothrombotic transformation of the vascular wall. The dual and opposing roles of LRP1 may also represent an interesting target for atherosclerosis therapeutics. This review highlights the influence of LRP1 during atherosclerosis development, focusing on its dual role in vascular cells and immune cells.

The molecular mechanism of LRP1 in physiological vascular homeostasis and signal transduction pathways

Interactions between vascular smooth muscle cells (VSMCs), endothelial cells (ECs), pericytes (PCs) and macrophages (MФ), the major components of blood vessels, play a crucial role in maintaining vascular structural and functional homeostasis. Low-density lipoprotein (LDL) receptor-related protein-1 (LRP1), a transmembrane receptor protein belonging to the LDL receptor family, plays multifunctional roles in maintaining endocytosis, homeostasis, and signal transduction. Accumulating evidence suggests that LRP1 modulates vascular homeostasis mainly by regulating vasoactive substances and specific intracellular signaling pathways, including the plasminogen activator inhibitor 1 (PAI-1) signaling pathway, platelet-derived growth factor (PDGF) signaling pathway, transforming growth factor-β (TGF-β) signaling pathway and vascular endothelial growth factor (VEGF) signaling pathway. The aim of the present review is to focus on recent advances in the discovery and mechanism of vascular homeostasis regulated by LRP1-dependent signaling pathways. These recent discoveries expand our understanding of the mechanisms controlling LRP1 as a target for studies on vascular complications.

Lrp1 Regulation of Pulmonary Function. Follow-Up of Human GWAS in Mice

Human genome-wide association studies (GWASs) have identified more than 270 loci associated with pulmonary function; however, follow-up studies to determine causal genes at these loci are few. SNPs in low-density lipoprotein receptor-related protein 1 (LRP1) are associated with human pulmonary function in GWASs. Using murine models, we investigated the effect of genetic disruption of the Lrp1 gene in smooth muscle cells on pulmonary function in naive animals and after exposure to bacterial LPS or house dust mite extract. Disruption of Lrp1 in smooth muscle cells leads to an increase in tissue resistance, elastance, and tissue elastance at baseline. Furthermore, disruption of Lrp1 in smooth muscle increases airway responsiveness as measured by increased total lung resistance and airway resistance after methacholine. Immune cell counts in BAL fluid were increased in animals with Lrp1 disruption. The difference in airway responsiveness by genotype observed in naive animals was not observed after LPS or house dust mite extract exposure. To further explore the mechanisms contributing to changes in pulmonary function, we identified several ligands dysregulated with Lrp1 disruption in smooth muscle cells. These data suggest that dysregulation of LRP1 in smooth muscle cells affects baseline pulmonary function and airway responsiveness and helps establish LRP1 as the causal gene at this GWAS locus.

From the low-density lipoprotein receptor-related protein 1 to neuropathic pain: a potentially novel target

The low-density lipoprotein receptor–related protein 1 plays a major role in the regulation of neuroinflammation, neurodegeneration, neuroregeneration, neuropathic pain, and deficient cognitive functions.

This review describes the roles of the low-density lipoprotein receptor–related protein 1 (LRP-1) in inflammatory pathways, nerve nerve degeneration and -regeneration and in neuropathic pain. Induction of LRP-1 is able to reduce the activation of the proinflammatory NFκB-mediated pathway and the mitogen-activated protein kinase (MAPK) c-Jun N-terminal kinase and p38 signaling pathways, in turn decreasing the production of inflammatory mediators. Low-density lipoprotein receptor-related protein 1 activation also decreases reactive astrogliosis and polarizes microglial cells and macrophages from a proinflammatory phenotype (M1) to an anti-inflammatory phenotype (M2), attenuating the neuroinflammatory environment. Low-density lipoprotein receptor-related protein 1 can also modulate the permeability of the blood–brain barrier and the blood–nerve barrier, thus regulating the infiltration of systemic insults and cells into the central and the peripheral nervous system, respectively. Furthermore, LRP-1 is involved in the maturation of oligodendrocytes and in the activation, migration, and repair phenotype of Schwann cells, therefore suggesting a major role in restoring the myelin sheaths upon injury. Low-density lipoprotein receptor-related protein 1 activation can indirectly decrease neurodegeneration and neuropathic pain by attenuation of the inflammatory environment. Moreover, LRP-1 agonists can directly promote neural cell survival and neurite sprouting, decrease cell death, and attenuate pain and neurological disorders by the inhibition of MAPK c-Jun N-terminal kinase and p38-pathway and activation of MAPK extracellular signal–regulated kinase pathway. In addition, activation of LRP-1 resulted in better outcomes for neuropathies such as Alzheimer disease, nerve injury, or diabetic peripheral neuropathy, attenuating neuropathic pain and improving cognitive functions. To summarize, LRP-1 plays an important role in the development of different experimental diseases of the nervous system, and it is emerging as a very interesting therapeutic target.

BMPER Ameliorates Renal Fibrosis by Inhibiting Tubular Dedifferentiation and Fibroblast Activation

Tubulointerstitial fibrosis is both a pathological manifestation of chronic kidney disease and a driving force for the progression of kidney disease. A previous study has shown that bone morphogenetic protein-binding endothelial cell precursor-derived regulator (BMPER) is involved in lung fibrogenesis. However, the role of BMPER in renal fibrosis remains unknown. In the present study, the expression of BMPER was examined by real-time PCR, Western blot and immunohistochemical staining. The in vitro effects of BMPER on tubular dedifferentiation and fibroblast activation were analyzed in cultured HK-2 and NRK-49F cells. The in vivo effects of BMPER were dissected in unilateral ureteral obstruction (UUO) mice by delivery of BMPER gene via systemic administration of plasmid vector. We reported that the expression of BMPER decreased in the kidneys of UUO mice and HK-2 cells. TGF-β1 increased inhibitor of differentiation-1 (Id-1) and induced epithelial mesenchymal transition in HK-2 cells, and knockdown of BMPER aggravated Id-1 up-regulation, E-cadherin loss, and tubular dedifferentiation. On the contrary, exogenous BMPER inhibited Id-1 up-regulation, prevented E-cadherin loss and tubular dedifferentiation after TGF-β1 exposure. In addition, exogenous BMPER suppressed fibroblast activation by hindering Erk1/2 phosphorylation. Knockdown of low-density lipoprotein receptor-related protein 1 abolished the inhibitory effect of BMPER on Erk1/2 phosphorylation and fibroblast activation. Moreover, delivery of BMPER gene improved renal tubular damage and interstitial fibrosis in UUO mice. Therefore, BMPER inhibits TGF-β1-induced tubular dedifferentiation and fibroblast activation and may hold therapeutic potential for tubulointerstitial fibrosis.

A clinical study on plasma biomarkers for deciding the use of adjuvant corticosteroid therapy in bronchopulmonary dysplasia of premature infants

Objective: The study was designed to investigate some plasma markers which help us to decide the use of adjuvant corticosteroid therapy in bronchopulmonary dysplasia (BPD) of premature infants. Methods: Thirty BPD infants were treated by dexamethasone. Among these cases, dexamethasone was significant effective in 10 cases, and no significant effective in 20 cases. These patients were divided into two groups as the significant effect (SE) group (n=10) and the non-significant effect (NE) group (n=20) according to the curative effect of dexamethasone. Fifteen non-BPD infants with gestational age and gender matching were selected as the control group. Plasma samples before and after dexamethasone treatment were collected from three infants chosen randomly from SEG for the data-independent acquisition (DIA) analysis. ELISA was further used to detect the levels of differential proteins LRP1 and S100A8 in all individuals, including SE, NE and control groups. Results: DIA analysis results showed that after dexamethasone treatment, there were a total of 52 plasma proteins that showed significant differences, of which 43 proteins were down-regulated and 9 proteins were up-regulated. LRP1 and S100A8 were two plasma proteins that were significantly changed after dexamethasone treatment. Compared with the control group, plasma LRP1 was significantly increased in BPD. Interestingly, the plasma concentration of LRP1 in the NE group was significantly higher than that in the SE group. S100A8, as an indicator of plasma inflammation, was significantly higher in BPD than the control group. Unlike LRP1, there was no significantly difference between the SE and NE group (P=0.279) before dexamethasone treatment. Conclusion: Elevated plasma LRP1 and S100A8 in BPD infants are two indicators that correlated with the efficacy of dexamethasone, and might be used as biomarkers for deciding the use of adjuvant corticosteroids therapy in the BPD.

LRP1 knockdown aggravates Aβ1-42-stimulated microglial and astrocytic neuroinflammatory responses by modulating TLR4/NF-κB/MAPKs signaling pathways

Neuroinflammation is an important pathological feature and an early event in the pathogenesis of Alzheimer's disease (AD), which is characterized by activation of microglia and astrocytes. Low-density lipoprotein receptor-related protein 1 (LRP1) is an endocytic receptor that is abundantly expressed in neurons, microglia, and astrocytes, and plays a critical role in AD pathogenesis. There is increasing evidence to show that LRP1 regulates inflammatory responses by modulating the release of pro-inflammatory cytokines and phagocytosis. However, the effects of LRP1 on β-amyloid protein (Aβ)-induced microglial and astrocytic neuroinflammatory responses and its underlying mechanisms have not been studied in detail. In the present study, knockdown of LRP1 significantly enhanced Aβ_1-42-stimulated neuroinflammation by increasing the production of pro-inflammatory cytokines in both BV2 microglial cells and mouse primary astrocytes. Furthermore, it is revealed that LRP1 knockdown further led to the activation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinases (MAPKs) signaling pathways. The phosphorylation of IκBα, p38, and JNK was significantly up-regulated in LRP1 knockdown BV2 microglial cells and primary astrocytes. Meanwhile, LRP1 knockdown increased expression of the NF-κB p65 subunit in the nucleus while decreased its expression in the cytoplasm. Besides, the upstream signaling adaptor molecules such as toll-like receptor 4 (TLR4), myeloid differentiation primary response protein 88 (MyD88), and tumor necrosis factor receptor-associated factor 6 (TRAF6) were also further increased. Moreover, blockade of NF-κB, p38, and JNK inhibited the production of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) induced by the knockdown of LRP1. Taken together, these findings indicated that LRP1 as an effective therapeutic target against AD and other neuroinflammation related diseases.

Silencing of LRP1 Exacerbates Inflammatory Response Via TLR4/NF-κB/MAPKs Signaling Pathways in APP/PS1 Transgenic Mice

Activation of glial cells (including microglia and astrocytes) appears central to the initiation and progression of neuroinflammation in Alzheimer's disease (AD). The low-density lipoprotein receptor-related protein 1 (LRP1) is a major receptor for amyloid-β (Aβ), which plays a critical role in AD pathogenesis. LRP1 regulates inflammatory response by modulating the release of pro-inflammatory cytokines and phagocytosis. However, the effects of LRP1 on microglia- and astrocytic cell-mediated neuroinflammation and their underlying mechanisms in AD remain unclear. Therefore, using APP/PS1 transgenic mice, we found that LRP1 is downregulated during disease progression. Silencing of brain LRP1 markedly exacerbated AD-related neuropathology including Aβ deposition, neuroinflammation, and synaptic and neuronal loss, which was accompanied by a decline in spatial cognitive ability. Further mechanistic study revealed that silencing of LRP1 initiated neuroinflammation by increasing microgliosis and astrogliosis, enhancing pro-inflammatory cytokine production, and regulating toll-like receptor 4 (TLR4)-mediated activation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways. Taken together, these findings indicated that LRP1 suppresses microglia and astrocytic cell activation by modulating TLR4/NF-κB/MAPK signaling pathways. Our results further provide insights into the role of LRP1 in AD pathogenesis and highlight LRP1 as a potential therapeutic target for the treatment of AD.

Deregulated expression of Elastin Microfibril Interfacer 2 (EMILIN2) in gastric cancer affects tumor growth and angiogenesis

Gastric cancer is a frequent human tumor and often a lethal disease. Targeted therapy for gastric carcinomas is far behind vis-à-vis other solid tumors, primarily because of the paucity of cancer-driving mutations that could be efficiently and specifically targeted by current therapy. Thus, there is a need to discover actionable pathways/proteins and new diagnostic and prognostic biomarkers. In this study, we explored the role of the extracellular matrix glycoprotein EMILIN2, Elastin Microfibril Interfacer 2, in a cohort of gastric cancer patients. We discovered that EMILIN2 expression was consistently suppressed in gastric cancer and high expression levels of this glycoprotein were linked to abnormal vascular density. Furthermore, we found that EMILIN2 had a dual effect on gastric carcinoma cells: on one hand, it decreased tumor cell proliferation by triggering apoptosis, and on the other hand, it evoked the production of a number of cytokines involved in angiogenesis and inflammation, such as IL-8. Collectively, our findings posit EMILIN2 as an important onco-regulator exerting pleiotropic effects on the gastric cancer microenvironment.

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EMILIN2 is localized in the gastric lamina propria and its expression is down-regulated in gastric cancer.

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High levels of EMILIN2 associate with elevated vascular density.

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EMILIN2 impairs the proliferation of gastric cancer cells by evoking apoptosis.

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Surprisingly, EMILIN2 triggers the expression of pro-angiogenic and pro-inflammatory cytokines.

Loss of LRP1 promotes acquisition of contractile-myofibroblast phenotype and release of active TGF-β1 from ECM stores

In healing tissue, fibroblasts differentiate to α-smooth muscle actin (SMA)-expressing contractile-myofibroblasts, which pull the wound edges together ensuring proper tissue repair. Uncontrolled expansion of the myofibroblast population may, however, lead to excessive tissue scarring and finally to organ dysfunction. Here, we demonstrate that the loss of low-density lipoprotein receptor-related protein (LRP) 1 overactivates the JNK1/2-c-Jun-Fra-2 signaling pathway leading to the induction of α-SMA and periostin expression in human lung fibroblasts (hLF). These changes are accompanied by increased contractility of the cells and the integrin- and protease-dependent release of active transforming growth factor (TGF)-β1 from the extracellular matrix (ECM) stores. Liberation of active TGF-β1 from the ECM further enhances α-SMA and periostin expression thus accelerating the phenotypic switch of hLF. Global gene expression profiling of LRP1-depleted hLF revealed that the loss of LRP1 affects cytoskeleton reorganization, cell-ECM contacts, and ECM production. In line with these findings, fibrotic changes in the skin and lung of Fra-2 transgenic mice were associated with LRP1 depletion and c-Jun overexpression. Altogether, our results suggest that dysregulation of LRP1 expression in fibroblasts in healing tissue may lead to the unrestrained expansion of contractile myofibroblasts and thereby to fibrosis development. Further studies identifying molecules, which regulate LRP1 expression, may provide new therapeutic options for largely untreatable human fibrotic diseases.

Gastrodin relieves inflammation injury induced by lipopolysaccharides in MRC-5 cells by up-regulation of miR-103

The beneficial function of gastrodin towards many inflammatory diseases has been identified. This study designed to see the influence of gastrodin in a cell model of chronic obstructive pulmonary disease (COPD). MRC-5 cells were treated by LPS, before which gastrodin was administrated. The effects of gastrodin were evaluated by conducting CCK-8, FITC-PI double staining, Western blot, qRT-PCR and ELISA. Besides this, the downstream effector and signalling were studied to decode how gastrodin exerted its function. And dual-luciferase assay was used to detect the targeting link between miR-103 and lipoprotein receptor-related protein 1 (LRP1). LPS induced apoptosis and the release of MCP-1, IL-6 and TNF-α in MRC-5 cells. Pre-treating MRC-5 cells with gastrodin attenuated LPS-induced cell damage. Meanwhile, p38/JNK and NF-κB pathways induced by LPS were repressed by gastrodin. miR-103 expression was elevated by gastrodin. Further, the protective functions of gastrodin were attenuated by miR-103 silencing. And LRP1 was a target of miR-103 and negatively regulated by miR-103. The in vitro data illustrated the protective function of gastrodin in LPS-injured MRC-5 cells. Gastrodin exerted its function possibly by up-regulating miR-103 and modulating p38/JNK and NF-κB pathways.

Thrombospondin 1 and Its Diverse Roles as a Regulator of Extracellular Matrix in Fibrotic Disease

Thrombospondin 1 (TSP1) is a matricellular extracellular matrix protein that has diverse roles in regulating cellular processes important for the pathogenesis of fibrotic diseases. We will present evidence for the importance of TSP1 control of latent transforming growth factor beta activation in renal fibrosis with an emphasis on diabetic nephropathy. Other functions of TSP1 that affect renal fibrosis, including regulation of inflammation and capillary density, will be addressed. Emerging roles for TSP1 N-terminal domain regulation of collagen matrix assembly, direct effects of TSP1-collagen binding, and intracellular functions of TSP1 in mediating endoplasmic reticulum stress responses in extracellular matrix remodeling and fibrosis, which could potentially affect renal fibrogenesis, will also be discussed. Finally, we will address possible strategies for targeting TSP1 functions to treat fibrotic renal disease.

Low Density Lipoprotein Receptor-Related Protein-1 in Cardiac Inflammation and Infarct Healing

Acute myocardial infarction (AMI) leads to myocardial cell death and ensuing sterile inflammatory response, which represents an attempt to clear cellular debris and promote cardiac repair. However, an overwhelming, unopposed or unresolved inflammatory response following AMI leads to further injury, worse remodeling and heart failure (HF). Additional therapies are therefore warranted to blunt the inflammatory response associated with ischemia and reperfusion and prevent long-term adverse events. Low-density lipoprotein receptor-related protein 1 (LRP1) is a ubiquitous endocytic cell surface receptor with the ability to recognize a wide range of structurally and functionally diverse ligands. LRP1 transduces multiple intracellular signal pathways regulating the inflammatory reaction, tissue remodeling and cell survival after organ injury. In preclinical studies, activation of LRP1-mediated signaling in the heart with non-selective and selective LRP1 agonists is linked with a powerful cardioprotective effect, reducing infarct size and cardiac dysfunction after AMI. The data from early phase clinical studies with plasma-derived α1-antitrypsin (AAT), an endogenous LRP1 agonist, and SP16 peptide, a synthetic LRP1 agonist, support the translational value of LRP1 as a novel therapeutic target in AMI. In this review, we will summarize the cellular and molecular bases of LRP1 functions in modulating the inflammatory reaction and the reparative process after injury in various peripheral tissues, and discuss recent evidences implicating LRP1 in myocardial inflammation and infarct healing.

Developing LRP1 Agonists into a Therapeutic Strategy in Acute Myocardial Infarction

Cardioprotection refers to a strategy aimed at enhancing survival pathways in the injured yet salvageable myocardium following ischemia-reperfusion. Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional receptor that can be targeted following reperfusion, to induce a cardioprotective signaling through the activation of the reperfusion injury salvage kinase (RISK) pathway. The data from preclinical studies with non-selective and selective LRP1 agonists are promising, showing a large therapeutic window for intervention to reduce infarct size after ischemia-reperfusion. A pilot clinical trial with plasma derived α1-antitrypsin (AAT), a naturally occurring LRP1 agonist, supports the translational value of LRP1 as a novel therapeutic target for cardioprotection. A phase I study with a selective LRP1 agonist has been completed showing no toxicity. These findings may open the way to early phase clinical studies with pharmacologic LRP1 activation in patients with acute myocardial infarction (AMI).

Decoding fibrosis: Mechanisms and translational aspects

Fibrosis, a complex process of abnormal tissue healing which inevitably leads to loss of physiological organ structure and function, is a worldwide leading cause of death. Despite a large body of research over the last two decades, antifibrotic approaches are mainly limited to organ replacement therapy generating high costs of medical care. In this translational issue, a unique group of basic and clinical researchers provide meaningful answers to a desperate call of society for effective antifibrotic treatments. Fortunately, a plethora of novel fibrogenic factors and biomarkers has been identified. Noninvasive diagnostic methods and drug delivery systems have been recently developed for the management of fibrosis. Consequently, a large number of exciting clinical trials addressing comprehensive, organ and stage-specific mechanisms of fibrogenesis are ongoing. By critically addressing previously unsuccessful and novel promising therapeutic strategies, we aim to spread hope for future treatments of the various forms of organ fibrosis.