Inactivation of catalytic and non-catalytic PI3 kinase gamma functions enhances hypoxia-induced pulmonary hypertension in mice

Rationale

Pulmonary hypertension (PH) is a pulmonary vascular disease characterised by chronically elevated pulmonary arterial mean pressure, increased pulmonary vascular resistance and right ventricular (RV) dysfunction and hypertrophy. The pathogenesis includes vasoconstriction of pulmonary vessels and pulmonary vascular remodelling. Phosphatidylinositol 3'-kinase γ (PI3Kγ) is highly expressed in leukocytes, endothelial cells (EC) and cardiomyocytes, which are involved in the pathogenesis of PH. The catalytic function of PI3Kγ has been shown to be associated with numerous processes that are potentially important for both vascular remodelling and maladaptive cardiac hypertrophy, including leukocyte recruitment and endothelial cell proliferation and survival. However, inhibition of non-catalytic PI3Kγ function results in reduced nitric oxide (NO) production by endothelial NO synthase (eNOS), which may lead to increased vascular resistance. Therefore, the aim of our study was to investigate the role of both catalytic and non-catalytic PI3Kγ functions in the pathogenesis of PH.

Methods

The importance of PI3Kγ in the pathogenesis of PH was analysed in vivo using the hypoxia-induced mouse model of PH (21 days at 10% O2 hypoxia (HOX)). PI3Kγ knockout mice (PI3Kγ−/−), as well as mice expressing a catalytically inactive form of PI3Kγ (PI3KγKD/KD) were investigated. To specifically inhibit the non-catalytic function of PI3Kγ, C57BL/6N mice were treated with a blocking peptide via intratracheal instillation and studied in the same model. Subsequently, systolic right ventricular pressure (RVSP) was measured using a Millar pressure catheter inserted via the jugular vein. In vitro, western blotting was used to investigate the phosphorylation of eNOS (Ser1177) in pulmonary ECs from wild type (WT), PI3Kγ−/− and PI3KγKD/KD mice.

Results

PI3Kγ−/− mice showed significantly increased RVSP after three weeks of hypoxia compared with WT controls (HOX WT 34.16±3.47mmHg vs. HOX PI3Kγ−/− 37.04±2.43mmHg; p=0.005; n≥7). A significant increase in RVSP was also detected in PI3KγKD/KD and blocking peptide-treated mice (HOX WT 34.67±2.02mmHg vs. HOX PI3KγKD/KD 37.95±1.39mmHg; p=0.023; n≥5 and HOX vehicle 34.19±2.74mmHg vs. HOX blocking peptide 37.61±2.46mmHg; p=0.011; n≥9). Heart rate, as well as systemic blood pressure, remained unchanged. Under normoxic conditions, no difference in RVSP between the groups could be measured. Interestingly, western blot detected reduced phosphorylation of eNOS after stimulation with fetal calf serum in PI3Kγ−/− ECs compared to WT and PI3KγKD/KD.

Conclusion

These results show that blunting of both catalytic and non-catalytic functions of PI3Kγ in vivo do not prevent the pathogenesis of PH, but conversely enhance hypoxia-induced elevation of RVSP. In this context, reduced phosphorylation of eNOS may play a crucial role, leading to increased vasoconstriction. Additional studies are required to evaluate the underlying mechanisms in detail.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): DFG Deutsche Forschungsgemeinschaft

Iron supplementation is sufficient to rescue skeletal muscle mass and function in cancer cachexia

Cachexia is a wasting syndrome characterized by devastating skeletal muscle atrophy that dramatically increases mortality in various diseases, most notably in cancer patients with a penetrance of up to 80%. Knowledge regarding the mechanism of cancer-induced cachexia remains very scarce, making cachexia an unmet medical need. In this study, we discovered strong alterations of iron metabolism in the skeletal muscle of both cancer patients and tumor-bearing mice, characterized by decreased iron availability in mitochondria. We found that modulation of iron levels directly influences myotube size in vitro and muscle mass in otherwise healthy mice. Furthermore, iron supplementation was sufficient to preserve both muscle function and mass, prolong survival in tumor-bearing mice, and even rescues strength in human subjects within an unexpectedly short time frame. Importantly, iron supplementation refuels mitochondrial oxidative metabolism and energy production. Overall, our findings provide new mechanistic insights in cancer-induced skeletal muscle wasting, and support targeting iron metabolism as a potential therapeutic option for muscle wasting diseases.

Docking Protein p130Cas Regulates Acinar to Ductal Metaplasia During Pancreatic Adenocarcinoma Development and Pancreatitis

BACKGROUND & AIMS

Acinar to ductal metaplasia is the prerequisite for the initiation of Kras-driven pancreatic ductal adenocarcinoma (PDAC), and candidate genes regulating this process are emerging from genome-wide association studies. The adaptor protein p130Cas emerged as a potential PDAC susceptibility gene and a Kras-synthetic lethal interactor in pancreatic cell lines; however, its role in PDAC development has remained largely unknown.

METHODS

Human PDAC samples and murine KrasG12D-dependent pancreatic cancer models of increasing aggressiveness were used. p130Cas was conditionally ablated in pancreatic cancer models to investigate its role during Kras-induced tumorigenesis.

RESULTS

We found that high expression of p130Cas is frequently detected in PDAC and correlates with higher histologic grade and poor prognosis. In a model of Kras-driven PDAC, loss of p130Cas inhibits tumor development and potently extends median survival. Deletion of p130Cas suppresses acinar-derived tumorigenesis and progression by means of repressing PI3K-AKT signaling, even in the presence of a worsening condition like pancreatitis.

CONCLUSIONS

Our observations finally demonstrated that p130Cas acts downstream of Kras to boost the PI3K activity required for acinar to ductal metaplasia and subsequent tumor initiation. This demonstrates an unexpected driving role of p130Cas downstream of Kras through PI3K/AKT, thus indicating a rational therapeutic strategy of targeting the PI3K pathway in tumors with high expression of p130Cas.

A PI3Kγ mimetic peptide triggers CFTR gating, bronchodilation, and reduced inflammation in obstructive airway diseases

Cyclic adenosine 3',5'-monophosphate (cAMP)-elevating agents, such as β₂-adrenergic receptor (β₂-AR) agonists and phosphodiesterase (PDE) inhibitors, remain a mainstay in the treatment of obstructive respiratory diseases, conditions characterized by airway constriction, inflammation, and mucus hypersecretion. However, their clinical use is limited by unwanted side effects because of unrestricted cAMP elevation in the airways and in distant organs. Here, we identified the A-kinase anchoring protein phosphoinositide 3-kinase γ (PI3Kγ) as a critical regulator of a discrete cAMP signaling microdomain activated by β₂-ARs in airway structural and inflammatory cells. Displacement of the PI3Kγ-anchored pool of protein kinase A (PKA) by an inhaled, cell-permeable, PI3Kγ mimetic peptide (PI3Kγ MP) inhibited a pool of subcortical PDE4B and PDE4D and safely increased cAMP in the lungs, leading to airway smooth muscle relaxation and reduced neutrophil infiltration in a murine model of asthma. In human bronchial epithelial cells, PI3Kγ MP induced unexpected cAMP and PKA elevations restricted to the vicinity of the cystic fibrosis transmembrane conductance regulator (CFTR), the ion channel controlling mucus hydration that is mutated in cystic fibrosis (CF). PI3Kγ MP promoted the phosphorylation of wild-type CFTR on serine-737, triggering channel gating, and rescued the function of F508del-CFTR, the most prevalent CF mutant, by enhancing the effects of existing CFTR modulators. These results unveil PI3Kγ as the regulator of a β₂-AR/cAMP microdomain central to smooth muscle contraction, immune cell activation, and epithelial fluid secretion in the airways, suggesting the use of a PI3Kγ MP for compartment-restricted, therapeutic cAMP elevation in chronic obstructive respiratory diseases.

PI3K Signaling in Mechanisms and Treatments of Pulmonary Fibrosis Following Sepsis and Acute Lung Injury

Pulmonary fibrosis is a pathological fibrotic process affecting the lungs of five million people worldwide. The incidence rate will increase even more in the next years due to the long-COVID-19 syndrome, but a resolving treatment is not available yet and usually prognosis is poor. The emerging role of the phosphatidylinositol 3-kinase (PI3K)/AKT signaling in fibrotic processes has inspired the testing of drugs targeting the PI3K/Akt pathway that are currently under clinical evaluation. This review highlights the progress in understanding the role of PI3K/Akt in the development of lung fibrosis and its causative pathological context, including sepsis as well as acute lung injury (ALI) and its consequent acute respiratory distress syndrome (ARDS). We further summarize current knowledge about PI3K inhibitors for pulmonary fibrosis treatment, including drugs under development as well as in clinical trials. We finally discuss how the design of inhaled compounds targeting the PI3K pathways might potentiate efficacy and improve tolerability.

Phosphoinositide Conversion Inactivates R-RAS and Drives Metastases in Breast Cancer

Breast cancer is the most prevalent cancer and a major cause of death in women worldwide. Although early diagnosis and therapeutic intervention significantly improve patient survival rate, metastasis still accounts for most deaths. Here it is reported that, in a cohort of more than 2000 patients with breast cancer, overexpression of PI3KC2α occurs in 52% of cases and correlates with high tumor grade as well as increased probability of distant metastatic events, irrespective of the subtype. Mechanistically, it is demonstrated that PI3KC2α synthetizes a pool of PI(3,4)P2 at focal adhesions that lowers their stability and directs breast cancer cell migration, invasion, and metastasis. PI(3,4)P2 locally produced by PI3KC2α at focal adhesions recruits the Ras GTPase activating protein 3 (RASA3), which inactivates R-RAS, leading to increased focal adhesion turnover, migration, and invasion both in vitro and in vivo. Proof-of-concept is eventually provided that inhibiting PI3KC2α or lowering RASA3 activity at focal adhesions significantly reduces the metastatic burden in PI3KC2α-overexpressing breast cancer, thereby suggesting a novel strategy for anti-breast cancer therapy.

Structural basis of phosphatidylinositol 3-kinase C2α function

Phosphatidylinositol 3-kinase type 2α (PI3KC2α) is an essential member of the structurally unresolved class II PI3K family with crucial functions in lipid signaling, endocytosis, angiogenesis, viral replication, platelet formation and a role in mitosis. The molecular basis of these activities of PI3KC2α is poorly understood. Here, we report high-resolution crystal structures as well as a 4.4-Å cryogenic-electron microscopic (cryo-EM) structure of PI3KC2α in active and inactive conformations. We unravel a coincident mechanism of lipid-induced activation of PI3KC2α at membranes that involves large-scale repositioning of its Ras-binding and lipid-binding distal Phox-homology and C-C2 domains, and can serve as a model for the entire class II PI3K family. Moreover, we describe a PI3KC2α-specific helical bundle domain that underlies its scaffolding function at the mitotic spindle. Our results advance our understanding of PI3K biology and pave the way for the development of specific inhibitors of class II PI3K function with wide applications in biomedicine.

OUP accepted manuscript

Epilepsy is one of the most frequent neurological diseases, with focal epilepsy accounting for the largest number of cases. The genetic alterations involved in focal epilepsy are far from being fully elucidated.

Here, we show that defective lipid signalling caused by heterozygous ultra-rare variants in PIK3C2B, encoding for the class II phosphatidylinositol 3-kinase PI3K-C2β, underlie focal epilepsy in humans. We demonstrate that patients’ variants act as loss-of-function alleles, leading to impaired synthesis of the rare signalling lipid phosphatidylinositol 3,4-bisphosphate, resulting in mTORC1 hyperactivation. In vivo, mutant Pik3c2b alleles caused dose-dependent neuronal hyperexcitability and increased seizure susceptibility, indicating haploinsufficiency as a key driver of disease. Moreover, acute mTORC1 inhibition in mutant mice prevented experimentally induced seizures, providing a potential therapeutic option for a selective group of patients with focal epilepsy.

Our findings reveal an unexpected role for class II PI3K-mediated lipid signalling in regulating mTORC1-dependent neuronal excitability in mice and humans.

PI(3,4)P2-mediated cytokinetic abscission prevents early senescence and cataract formation

Cytokinetic membrane abscission is a spatially and temporally regulated process that requires ESCRT (endosomal sorting complexes required for transport)–dependent control of membrane remodeling at the midbody, a subcellular organelle that defines the cleavage site. Alteration of ESCRT function can lead to cataract, but the underlying mechanism and its relation to cytokinesis are unclear. We found a lens-specific cytokinetic process that required PI3K-C2α (phosphatidylinositol-4-phosphate 3-kinase catalytic subunit type 2α), its lipid product PI(3,4)P2 (phosphatidylinositol 3,4-bisphosphate), and the PI(3,4)P2–binding ESCRT-II subunit VPS36 (vacuolar protein-sorting-associated protein 36). Loss of each of these components led to impaired cytokinesis, triggering premature senescence in the lens of fish, mice, and humans. Thus, an evolutionarily conserved pathway underlies the cell type–specific control of cytokinesis that helps to prevent early onset cataract by protecting from senescence.

Phosphoproteomics Identifies PI3K Inhibitor-selective Adaptive Responses in Pancreatic Cancer Cell Therapy and Resistance

The PI3K pathway is highly active in human cancers. The four class I isoforms of PI3K are activated by distinct mechanisms leading to a common downstream signaling. Their downstream redundancy is thought to be responsible for treatment failures of PI3K inhibitors. We challenged this concept, by mapping the differential phosphoproteome evolution in response to PI3K inhibitors with different isoform-selectivity patterns in pancreatic cancer, a disease currently without effective therapy. In this cancer, the PI3K signal was shown to control cell proliferation. We compared the effects of LY294002 that inhibit with equal potency all class I isoenzymes and downstream mTOR with the action of inhibitors with higher isoform selectivity toward PI3Kα, PI3Kβ, or PI3Kγ (namely, A66, TGX-221 and AS-252424). A bioinformatics global pathway analysis of phosphoproteomics data allowed us to identify common and specific signals activated by PI3K inhibitors supported by the biological data. AS-252424 was the most effective treatment and induced apoptotic pathway activation as well as the highest changes in global phosphorylation-regulated cell signal. However, AS-252424 treatment induced reactivation of Akt, therefore decreasing the treatment outcome on cell survival. Reversely, AS-252424 and A66 combination treatment prevented p-Akt reactivation and led to synergistic action in cell lines and patient organoids. The combination of clinically approved α-selective BYL-719 with γ-selective IPI-549 was more efficient than single-molecule treatment on xenograft growth. Mapping unique adaptive signaling responses to isoform-selective PI3K inhibition will help to design better combinative treatments that prevent the induction of selective compensatory signals.

Preventing and Treating Anthracycline Cardiotoxicity: New Insights

Anthracyclines are the cornerstone of many chemotherapy regimens for a variety of cancers. Unfortunately, their use is limited by a cumulative dose-dependent cardiotoxicity. Despite more than five decades of research, the biological mechanisms underlying anthracycline cardiotoxicity are not completely understood. In this review, we discuss the incidence, risk factors, types, and pathophysiology of anthracycline cardiotoxicity, as well as methods to prevent and treat this condition. We also summarize and discuss advances made in the last decade in the comprehension of the molecular mechanisms underlying the pathology.

Chemical Oral Cancerogenesis Is Impaired in PI3Kγ Knockout and Kinase-Dead Mice

We investigated the role of PI3Kγ in oral carcinogenesis by using a murine model of oral squamous carcinoma generated by exposure to 4-nitroquinoline 1-oxide (4NQO) and the continuous human cancer cell line HSC-2 and Cal-27. PI3Kγ knockout (not expressing PI3Kγ), PI3Kγ kinase-dead (carrying a mutation in the PI3Kγ gene causing loss of kinase activity) and wild-type (WT) C57Bl/6 mice were administered 4NQO via drinking water to induce oral carcinomas. At sacrifice, lesions were histologically examined and stained for prognostic tumoral markers (EGFR, Neu, cKit, Ki67) and inflammatory infiltrate (CD3, CD4, CD8, CD19 and CD68). Prevalence and incidence of preneoplastic and exophytic lesions were significantly and similarly delayed in both transgenic mice versus the control. The expression of prognostic markers, as well as CD19⁺ and CD68⁺ cells, was higher in WT, while T lymphocytes were more abundant in tongues isolated from transgenic mice. HSC-2 and Cal-27 cells were cultured in the presence of the specific PI3Kγ-inhibitor (IPI-549) which significantly impaired cell vitality in a dose-dependent manner, as shown by the MTT test. Here, we highlighted two different mechanisms, namely the modulation of the tumor-infiltrating cells and the direct inhibition of cancer-cell proliferation, which might impair oral cancerogenesis in the absence/inhibition of PI3Kγ.

Impaired immune response mediated by prostaglandin E2 promotes severe COVID-19 disease

The SARS-CoV-2 coronavirus has led to a pandemic with millions of people affected. The present study finds that risk-factors for severe COVID-19 disease courses, i.e. male sex, older age and sedentary life style are associated with higher prostaglandin E2 (PGE2) serum levels in blood samples from unaffected subjects. In COVID-19 patients, PGE2 blood levels are markedly elevated and correlate positively with disease severity. SARS-CoV-2 induces PGE2 generation and secretion in infected lung epithelial cells by upregulating cyclo-oxygenase (COX)-2 and reducing the PG-degrading enzyme 15-hydroxyprostaglandin-dehydrogenase. Also living human precision cut lung slices (PCLS) infected with SARS-CoV-2 display upregulated COX-2. Regular exercise in aged individuals lowers PGE2 serum levels, which leads to increased Paired-Box-Protein-Pax-5 (PAX5) expression, a master regulator of B-cell survival, proliferation and differentiation also towards long lived memory B-cells, in human pre-B-cell lines. Moreover, PGE2 levels in serum of COVID-19 patients lowers the expression of PAX5 in human pre-B-cell lines. The PGE2 inhibitor Taxifolin reduces SARS-CoV-2-induced PGE2 production. In conclusion, SARS-CoV-2, male sex, old age, and sedentary life style increase PGE2 levels, which may reduce the early anti-viral defense as well as the development of immunity promoting severe disease courses and multiple infections. Regular exercise and Taxifolin treatment may reduce these risks and prevent severe disease courses.

PI3K as Mediator of Apoptosis and Contractile Dysfunction in TGFβ1-Stimulated Cardiomyocytes

BACKGROUND

TGFβ₁ is a growth factor that plays a major role in the remodeling process of the heart by inducing cardiomyocyte dysfunction and apoptosis, as well as fibrosis thereby restricting heart function. TGFβ₁ mediates its effect via the TGFβ receptor I (ALK5) and the activation of SMAD transcription factors, but TGFβ₁ is also known as activator of phosphoinositide-3-kinase (PI3K) via the non-SMAD signaling pathway. The aim of this study was to investigate whether PI3K is also involved in TGFβ₁-induced cardiomyocytes apoptosis and contractile dysfunction.

METHODS AND RESULTS

Incubation of isolated ventricular cardiomyocytes with TGFβ₁ resulted in impaired contractile function. Pre-incubation of cells with the PI3K inhibitor Ly294002 or the ALK5 inhibitor SB431542 attenuated the decreased cell shortening in TGFβ₁-stimulated cells. Additionally, TGFβ-induced apoptosis was significantly reduced by the PI3K inhibitor Ly294002. Administration of a PI3Kγ-specific inhibitor AS605240 abolished the TGFβ effect on apoptosis and cell shortening. This was also confirmed in cardiomyocytes from PI3Kγ KO mice. Induction of SMAD binding activity and the TGFβ target gene collagen 1 could be blocked by the PI3K inhibitor Ly294002, but not by the specific PI3Kγ inhibitor AS605240.

CONCLUSIONS

TGFβ₁-induced SMAD activation, cardiomyocyte apoptosis, and impaired cell shortening are mediated via both, the ALK5 receptor and PI3K, in adult cardiomyocytes. PI3Kγ specifically contributes to apoptosis induction and impairment of contractile function independent of SMAD signaling.

Targeting PI3K/AKT/mTOR Signaling Pathway in Breast Cancer

Breast cancer is the most frequently diagnosed cancer and the primary cause of cancer death in women worldwide. Although early diagnosis and cancer growth inhibition has significantly improved breast cancer survival rate over the years, there is a current need to develop more effective systemic treatments to prevent metastasis. One of the most commonly altered pathways driving breast cancer cell growth, survival, and motility is the PI3K/AKT/mTOR signaling cascade. In the past 30 years, a great surge of inhibitors targeting these key players has been developed at a rapid pace, leading to effective preclinical studies for cancer therapeutics. However, the central role of PI3K/AKT/mTOR signaling varies among diverse biological processes, suggesting the need for more specific and sophisticated strategies for their use in cancer therapy. In this review, we provide a perspective on the role of the PI3K signaling pathway and the most recently developed PI3K-targeting breast cancer therapies.

Targeting the extracellular HSP90 co-chaperone Morgana inhibits cancer cell migration and promotes anti-cancer immunity

Heat shock protein 90 (HSP90) is secreted by cancer cells into the extracellular milieu, where it exerts pro-tumoral activities by activating extracellular substrate proteins and triggering autocrine signals through cancer cell surface receptors. Emerging evidence indicates that HSP90 co-chaperones are also secreted and may direct HSP90 extracellular activities. In this study, we found that the HSP90 co-chaperone Morgana is released by cancer cells and, in association with HSP90, induces cancer cell migration through TLR2, TLR4, and LRP1. In syngeneic cancer mouse models, a monoclonal antibody targeting Morgana extracellular activity reduced primary tumor growth via macrophage-dependent recruitment of CD8+ T lymphocytes, blocked cancer cell migration, and inhibited metastatic spreading. Overall, this data defines Morgana as a new player in the HSP90 extracellular interactome and suggests that Morgana may regulate HSP90 activity to promote cancer cell migration and suppress anti-tumor immunity.

Role of Protein Kinase A-Mediated Phosphorylation in CFTR Channel Activity Regulation

Cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel expressed on the apical membrane of epithelial cells, where it plays a pivotal role in chloride transport and overall tissue homeostasis. CFTR constitutes a unique member of the ATP-binding cassette transporter superfamily, due to its distinctive cytosolic regulatory (R) domain carrying multiple phosphorylation sites that allow the tight regulation of channel activity and gating. Mutations in the CFTR gene cause cystic fibrosis, the most common lethal autosomal genetic disease in the Caucasian population. In recent years, major efforts have led to the development of CFTR modulators, small molecules targeting the underlying genetic defect of CF and ultimately rescuing the function of the mutant channel. Recent evidence has highlighted that this class of drugs could also impact on the phosphorylation of the R domain of the channel by protein kinase A (PKA), a key regulatory mechanism that is altered in various CFTR mutants. Therefore, the aim of this review is to summarize the current knowledge on the regulation of the CFTR by PKA-mediated phosphorylation and to provide insights into the different factors that modulate this essential CFTR modification. Finally, the discussion will focus on the impact of CF mutations on PKA-mediated CFTR regulation, as well as on how small molecule CFTR regulators and PKA interact to rescue dysfunctional channels.

Oxidative stress in anticancer therapies-related cardiac dysfunction

Redox abnormalities are at the crossroad of cardiovascular diseases, cancer and cardiotoxicity from anticancer treatments. Indeed, disturbances of the redox equilibrium are common drivers of these conditions. Not only is an increase in oxidative stress a fundamental mechanism of action of anthracyclines (which have historically been the most studied anticancer treatments) but also this is at the basis of the toxic cardiovascular effects of antineoplastic targeted drugs and radiotherapy. Here we examine the oxidative mechanisms involved in the different cardiotoxicities induced by the main redox-based antineoplastic treatments, and discuss novel approaches for the treatment of such toxicities.

Physics of compartmentalization: How phase separation and signaling shape membrane and organelle identity

Compartmentalization of cellular functions is at the core of the physiology of eukaryotic cells. Recent evidences indicate that a universal organizing process - phase separation - supports the partitioning of biomolecules in distinct phases from a single homogeneous mixture, a landmark event in both the biogenesis and the maintenance of membrane and non-membrane-bound organelles. In the cell, 'passive' (non energy-consuming) mechanisms are flanked by 'active' mechanisms of separation into phases of distinct density and stoichiometry, that allow for increased partitioning flexibility and programmability. A convergence of physical and biological approaches is leading to new insights into the inner functioning of this driver of intracellular order, holding promises for future advances in both biological research and biotechnological applications.

Protective Role of the M-Sec-Tunneling Nanotube System in Podocytes

BACKGROUND

Podocyte dysfunction and loss are major determinants in the development of proteinuria. FSGS is one of the most common causes of proteinuria, but the mechanisms leading to podocyte injury or conferring protection against FSGS remain poorly understood. The cytosolic protein M-Sec has been involved in the formation of tunneling nanotubes (TNTs), membrane channels that transiently connect cells and allow intercellular organelle transfer. Whether podocytes express M-Sec is unknown and the potential relevance of the M-Sec-TNT system in FSGS has not been explored.

METHODS

We studied the role of the M-Sec-TNT system in cultured podocytes exposed to Adriamycin and in BALB/c M-Sec knockout mice. We also assessed M-Sec expression in both kidney biopsies from patients with FSGS and in experimental FSGS (Adriamycin-induced nephropathy).

RESULTS

Podocytes can form TNTs in a M-Sec-dependent manner. Consistent with the notion that the M-Sec-TNT system is cytoprotective, podocytes overexpressed M-Sec in both human and experimental FSGS. Moreover, M-Sec deletion resulted in podocyte injury, with mitochondrial abnormalities and development of progressive FSGS. In vitro, M-Sec deletion abolished TNT-mediated mitochondria transfer between podocytes and altered mitochondrial bioenergetics. Re-expression of M-Sec reestablishes TNT formation and mitochondria exchange, rescued mitochondrial function, and partially reverted podocyte injury.

CONCLUSIONS

These findings indicate that the M-Sec-TNT system plays an important protective role in the glomeruli by rescuing podocytes via mitochondrial horizontal transfer. M-Sec may represent a promising therapeutic target in FSGS, and evidence that podocytes can be rescued via TNT-mediated horizontal transfer may open new avenues of research.

Roles of phosphatidyl inositol 3 kinase gamma (PI3Kγ) in respiratory diseases

Phosphatidyl inositol 3 kinase gamma (PI3Kγ) is expressed in all the cell types that are involved in airway inflammation and disease, including not only leukocytes, but also structural cells, where it is expressed at very low levels under physiological conditions, while is significantly upregulated after stress. In the airways, PI3Kγ behaves as a trigger or a controller, depending on the pathological context. In this review, the contribution of PI3Kγ in a plethora of respiratory diseases, spanning from acute lung injury, pulmonary fibrosis, asthma, cystic fibrosis and response to both bacterial and viral pathogens, will be commented.

Abstract LT018: The perivascular niche protects ALK+ lymphoma cells from ALK inhibition through the CCL19/21-CCR7 axis

The ALK inhibitor crizotinib showed promising therapeutic efficacy for relapsed/refractory Anaplastic Large Cell Lymphoma (R/R ALCL). However, a fraction of ALK+ R/R ALCL patients do not achieve complete remission due to crizotinib resistance that develops within the first 3 months of therapy. In patients that achieve complete remission, crizotinib discontinuation causes rapid disease relapses due to the expansion of persister lymphoma cells never completely eradicated by the ALK inhibitor. There is, in fact, growing evidence that ALK+ ALCL can persist for years in patients being undetectable. ALCL grows around blood and lymphatic vessels in the lymph node. We hypothesize that this perivascular niche provides pro-survival signals contributing to ALK+ ALCL persistence and TKI resistance. By RNA-seq analysis on ALK+ ALCL cells and scRNA-seq analysis in one ALK+ ALCL primary sample, we found that ALK+ cells expressed the C-C chemokine receptor type 7 (CCR7), while endothelial cells and fibroblasts expressed the unique CCR7 ligands, the chemokine (C-C motif) ligand 19 (CCL19) and 21 (CCL21). Therefore, we explored whether the CCL19/21-CCR7 chemokine-receptor signaling axis could be involved in the persistence of ALK+ ALCL cells during ALK inhibitor treatment. We show that treatment with crizotinib caused upregulation of CCR7 in ALK+ ALCL cells via STAT3, as demonstrated by ChIP-seq data. Besides, stimulation of ALK+ ALCL cells with both CCL19/21 potently activated the MAPK signaling and sustained MAPK activation during ALK inhibition by crizotinib. Mechanistically, we demonstrate that this MAPK activation was mediated by PI3Kγ-dependent CCR7 signaling. This effect was more marked in human ALK+ ALCL cells that express high levels of PI3Kγ, while it was strongly reduced in murine lymphoma PI3KγKO cells, generated from NPM-ALK transgenic mice crossed with PI3KγKO mice. Treatment with the PI3Kγ/δ dual inhibitor duvelisib abrogated the MAPK phosphorylation induced by CCL19/21. When we knocked-out the CCR7 gene via CRISPR/Cas9, human ALK+ ALCL showed markedly reduced activation of the MAPK pathway upon stimulation with CCL19/21. Next, we developed a microphysiological model of ALCL cells in the perivascular niche with a 3D vasculature using a microfluidic chip. In this model, ALCL cells circulate inside the chip in continuous contact with a perfusable vasculature. We, then, demonstrated that the presence of endothelial cells conferred resistance to crizotinib and sustained cell viability of CCR7WT cells, whereas the protective effect was lost in CCR7KO cells. In in vivo experiments, CCR7 was required for lymphoma cell survival and diffusion to the brain during crizotinib treatment. Overall, our results suggest that the perivascular niche could promote the survival of ALK+ ALCL persister cells and protect them from the effect of ALK TKIs via the CCL19/21-CCR7 axis. The disruption of this survival axis could contribute to eradicating minimal residual disease in combination with ALK TKI.

Citation Format: Cristina Mastini, Marco Campisi, Carlotta Costa, Chiara Ambrogio, Giulia Germena, Silvia Peola, Cinzia Martinengo, Enrico Patrucco, Ines Mota, Maddalena Arrigoni, Martina Olivero, Raffaele Calogero, Valeria Chiono, Roger D. Kamm, Emilio Hirsch, Jon C. Aster, Claudia Voena, Roberto Chiarle. The perivascular niche protects ALK+ lymphoma cells from ALK inhibition through the CCL19/21-CCR7 axis [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr LT018.