Brief reports: Lysosomal cross-correction by hematopoietic stem cell-derived macrophages via tunneling nanotubes

Targeted gene therapy for rare genetic kidney diseases

Chronic kidney disease (CKD) is one of the leading causes of mortality worldwide because of kidney failure and the associated challenges of its treatment including dialysis and kidney transplantation. About one-third of CKD cases are linked to inherited monogenic factors, making them suitable for potential gene therapy interventions. However, the intricate anatomical structure of the kidney poses a challenge, limiting the effectiveness of targeted gene delivery to the renal system. In this review, we explore the progress made in the field of targeted gene therapy approaches and their implications for rare genetic kidney disorders, examining preclinical studies and prospects for clinical application. In vivo gene therapy is most commonly used for kidney-targeted gene delivery and involves administering viral and non-viral vectors through various routes such as systemic, renal vein and renal arterial injections. Small nucleic acids have also been used in preclinical and clinical studies for treating certain kidney disorders. Unexpectedly, hematopoietic stem and progenitor cells have been used as an ex vivo gene therapy vehicle for kidney gene delivery, highlighting their ability to differentiate into macrophages within the kidney, forming tunneling nanotubes that can deliver genetic material and organelles to adjacent kidney cells, even across the basement membrane to target the proximal tubular cells. As gene therapy technologies continue to advance and our understanding of kidney biology deepens, there is hope for patients with genetic kidney disorders to eventually avoid kidney transplantation.

A review on Gaucher disease: therapeutic potential of β-glucocerebrosidase-targeted mRNA/saRNA approach

Gaucher disease (GD), a rare hereditary lysosomal storage disorder, occurs due to a deficiency in the enzyme β-glucocerebrosidase (GCase). This deficiency leads to the buildup of substrate glucosylceramide (GlcCer) in macrophages, eventually resulting in various complications. Among its three types, GD2 is particularly severe with neurological involvements. Current treatments, such as enzyme replacement therapy (ERT), are not effective for GD2 and GD3 due to their inability to cross the blood-brain barrier (BBB). Other treatment approaches, such as gene or chaperone therapies are still in experimental stages. Additionally, GD treatments are costly and can have certain side effects. The successful use of messenger RNA (mRNA)-based vaccines for COVID-19 in 2020 has sparked interest in nucleic acid-based therapies. Remarkably, mRNA technology also offers a novel approach for protein replacement purposes. Additionally, self-amplifying RNA (saRNA) technology shows promise, potentially producing more protein at lower doses. This review aims to explore the potential of a cost-effective mRNA/saRNA-based approach for GD therapy. The use of GCase-mRNA/saRNA as a protein replacement therapy could offer a new and promising direction for improving the quality of life and extending the lifespan of individuals with GD.

Diversity of Intercellular Communication Modes: A Cancer Biology Perspective

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

Intercellular Highways in Transport Processes

Communication among cells is vital in multicellular organisms. Various structures and mechanisms have evolved over time to achieve the intricate flow of material and information during this process. One such way of communication is through tunnelling membrane nanotubes (TNTs), which were initially described in 2004. These TNTs are membrane-bounded actin-rich cellular extensions, facilitating direct communication between distant cells. They exhibit remarkable diversity in terms of structure, morphology, and function, in which cytoskeletal proteins play an essential role. Biologically, TNTs play a crucial role in transporting membrane components, cell organelles, and nucleic acids, and they also present opportunities for the efficient transmission of bacteria and viruses, furthermore, may contribute to the dissemination of misfolded proteins in certain neurodegenerative diseases. Convincing results of studies conducted both in vitro and in vivo indicate that TNTs play roles in various biomedical processes, including cell differentiation, tissue regeneration, neurodegenerative diseases, immune response and function, as well as tumorigenesis.

Tunneling Nanotubes in Myeloid Cells: Perspectives for Health and Infectious Diseases

Tunneling nanotubes (TNTs) are cellular connections, which represent a novel route for cell-to-cell communication. Strong evidence points to a role for TNTs in the intercellular transfer of signals, molecules, organelles, and pathogens, involving them in many cellular functions. In myeloid cells (e.g., monocytes/macrophages, dendritic cells, and osteoclasts), intercellular communication via TNT contributes to their differentiation and immune functions, by favoring material and pathogen transfer, as well as cell fusion. This chapter addresses the complexity of the definition and characterization of TNTs in myeloid cells, the different processes involved in their formation, their existence in vivo, and finally their function(s) in health and infectious diseases, with the example of HIV-1 infection.

Tunneling Nanotubes: The Cables for Viral Spread and Beyond

Multicellular organisms require cell-to-cell communication to maintain homeostasis and thrive. For cells to communicate, a network of filamentous, actin-rich tunneling nanotubes (TNTs) plays a pivotal role in facilitating efficient cell-to-cell communication by connecting the cytoplasm of adjacent or distant cells. Substantial documentation indicates that diverse cell types employ TNTs in a sophisticated and intricately organized fashion for both long and short-distance communication. Paradoxically, several pathogens, including viruses, exploit the structural integrity of TNTs to facilitate viral entry and rapid cell-to-cell spread. These pathogens utilize a "surfing" mechanism or intracellular transport along TNTs to bypass high-traffic cellular regions and evade immune surveillance and neutralization. Although TNTs are present across various cell types in healthy tissue, their magnitude is increased in the presence of viruses. This heightened induction significantly amplifies the role of TNTs in exacerbating disease manifestations, severity, and subsequent complications. Despite significant advancements in TNT research within the realm of infectious diseases, further studies are imperative to gain a precise understanding of TNTs' roles in diverse pathological conditions. Such investigations are essential for the development of novel therapeutic strategies aimed at leveraging TNT-associated mechanisms for clinical applications. In this chapter, we emphasize the significance of TNTs in the life cycle of viruses, showcasing the potential for a targeted approach to impede virus-host cell interactions during the initial stages of viral infections. This approach holds promise for intervention and prevention strategies.

Tunneling Nanotubes in the Brain

Tunneling nanotubes (TNTs) have emerged as intriguing structures facilitating intercellular communications across diverse cell types, which are integral to several biological processes, as well as participating in various disease progression. This review provides an in-depth analysis of TNTs, elucidating their structural characteristics and functional roles, with a particular focus on their significance within the brain environment and their implications in neurological and neurodegenerative disorders. We explore the interplay between TNTs and neurological diseases, offering potential mechanistic insights into disease progression, while also highlighting their potential as viable therapeutic targets. Additionally, we address the significant challenges associated with studying TNTs, from technical limitations to their investigation in complex biological systems. By addressing some of these challenges, this review aims to pave the way for further exploration into TNTs, establishing them as a central focus in advancing our understanding of neurodegenerative disorders.

Evaluation of the efficacy of cystinosin supplementation through CTNS mRNA delivery in experimental models for cystinosis

Messenger RNA (mRNA) therapies are emerging in different disease areas, but have not yet reached the kidney field. Our aim was to study the feasibility to treat the genetic defect in cystinosis using synthetic mRNA in cell models and ctns-/- zebrafish embryos. Cystinosis is a prototype lysosomal storage disorder caused by mutations in the CTNS gene, encoding the lysosomal cystine-H+ symporter cystinosin, and leading to cystine accumulation in all cells of the body. The kidneys are the first and the most severely affected organs, presenting glomerular and proximal tubular dysfunction, progressing to end-stage kidney failure. The current therapeutic standard cysteamine, reduces cystine levels, but has many side effects and does not restore kidney function. Here, we show that synthetic mRNA can restore lysosomal cystinosin expression following lipofection into CTNS-/- kidney cells and injection into ctns-/- zebrafish. A single CTNS mRNA administration decreases cellular cystine accumulation for up to 14 days in vitro. In the ctns-/- zebrafish, CTNS mRNA therapy improves proximal tubular reabsorption, reduces proteinuria, and restores brush border expression of the multi-ligand receptor megalin. Therefore, this proof-of-principle study takes the first steps in establishing an mRNA-based therapy to restore cystinosin expression, resulting in cystine reduction in vitro and in the ctns-/- larvae, and restoration of the zebrafish pronephros function.

Ebola Virus Uses Tunneling Nanotubes as an Alternate Route of Dissemination

Ebola virus (EBOV) disease is marked by rapid virus replication and spread. EBOV enters the cell by macropinocytosis and replicates in the cytoplasm, and nascent virions egress from the cell surface to infect neighboring cells. Here, we show that EBOV uses an alternate route to disseminate: tunneling nanotubes (TNTs). TNTs, an actin-based long-range intercellular communication system, allows for direct exchange of cytosolic constituents between cells. Using live, scanning electron, and high-resolution quantitative 3-dimensional microscopy, we show that EBOV infection of primary human cells results in the enhanced formation of TNTs containing viral nucleocapsids. TNTs promote the intercellular transfer of nucleocapsids in the absence of live virus, and virus could replicate in cells devoid of entry factors after initial stall. Our studies suggest an alternate model of EBOV dissemination within the host, laying the groundwork for further investigations into the pathogenesis of filoviruses and, importantly, stimulating new areas of antiviral design.

Low-Dose Non-Targeted Effects and Mitochondrial Control

Non-targeted effects (NTE) have been generally regarded as a low-dose ionizing radiation (IR) phenomenon. Recently, regarding long distant abscopal effects have also been observed at high doses of IR) relevant to antitumor radiation therapy. IR is inducing NTE involving intracellular and extracellular signaling, which may lead to short-ranging bystander effects and distant long-ranging extracellular signaling abscopal effects. Internal and "spontaneous" cellular stress is mostly due to metabolic oxidative stress involving mitochondrial energy production (ATP) through oxidative phosphorylation and/or anaerobic pathways accompanied by the leakage of O₂^- and other radicals from mitochondria during normal or increased cellular energy requirements or to mitochondrial dysfunction. Among external stressors, ionizing radiation (IR) has been shown to very rapidly perturb mitochondrial functions, leading to increased energy supply demands and to ROS/NOS production. Depending on the dose, this affects all types of cell constituents, including DNA, RNA, amino acids, proteins, and membranes, perturbing normal inner cell organization and function, and forcing cells to reorganize the intracellular metabolism and the network of organelles. The reorganization implies intracellular cytoplasmic-nuclear shuttling of important proteins, activation of autophagy, and mitophagy, as well as induction of cell cycle arrest, DNA repair, apoptosis, and senescence. It also includes reprogramming of mitochondrial metabolism as well as genetic and epigenetic control of the expression of genes and proteins in order to ensure cell and tissue survival. At low doses of IR, directly irradiated cells may already exert non-targeted effects (NTE) involving the release of molecular mediators, such as radicals, cytokines, DNA fragments, small RNAs, and proteins (sometimes in the form of extracellular vehicles or exosomes), which can induce damage of unirradiated neighboring bystander or distant (abscopal) cells as well as immune responses. Such non-targeted effects (NTE) are contributing to low-dose phenomena, such as hormesis, adaptive responses, low-dose hypersensitivity, and genomic instability, and they are also promoting suppression and/or activation of immune cells. All of these are parts of the main defense systems of cells and tissues, including IR-induced innate and adaptive immune responses. The present review is focused on the prominent role of mitochondria in these processes, which are determinants of cell survival and anti-tumor RT.

Macrophages Promote Tumor Cell Extravasation across an Endothelial Barrier through Thin Membranous Connections

Macrophages are important players involved in the progression of breast cancer, including in seeding the metastatic niche. However, the mechanism by which macrophages in the lung parenchyma interact with tumor cells in the vasculature to promote tumor cell extravasation at metastatic sites is not clear. To mimic macrophage-driven tumor cell extravasation, we used an in vitro assay (eTEM) in which an endothelial monolayer and a matrigel-coated filter separated tumor cells and macrophages from each other. The presence of macrophages promoted tumor cell extravasation, while macrophage conditioned media was insufficient to stimulate tumor cell extravasation in vitro. This finding is consistent with a requirement for direct contact between macrophages and tumor cells. We observed the presence of Thin Membranous Connections (TMCs) resembling similar structures formed between macrophages and tumor cells called tunneling nanotubes, which we previously demonstrated to be important in tumor cell invasion in vitro and in vivo. To determine if TMCs are important for tumor cell extravasation, we used macrophages with reduced levels of endogenous M-Sec (TNFAIP2), which causes a defect in tunneling nanotube formation. As predicted, these macrophages showed reduced macrophage-tumor cell TMCs. In both, human and murine breast cancer cell lines, there was also a concomitant reduction in tumor cell extravasation in vitro when co-cultured with M-Sec deficient macrophages compared to control macrophages. We also detected TMCs formed between macrophages and tumor cells through the endothelial layer in the eTEM assay. Furthermore, tumor cells were more frequently found in pores under the endothelium that contain macrophage protrusions. To determine the role of macrophage-tumor cell TMCs in vivo, we generated an M-Sec deficient mouse. Using an in vivo model of experimental metastasis, we detected a significant reduction in the number of metastatic lesions in M-Sec deficient mice compared to wild type mice. There was no difference in the size of the metastases, consistent with a defect specific to tumor cell extravasation and not metastatic outgrowth. Additionally, with an examination of time-lapse intravital-imaging (IVI) data sets of breast cancer cell extravasation in the lungs, we could detect the presence of TMCs between extravascular macrophages and vascular tumor cells. Overall, our data indicate that macrophage TMCs play an important role in promoting the extravasation of circulating tumor cells in the lungs.

Mitochondrial transfer in PC-3 cells fingerprinted in ferroptosis sensitivity: a brand new approach targeting cancer metabolism

Despite recent therapeutic advancements, cancer remains one of the leading causes of death worldwide, with mitochondrial dysfunction being associated with cancer initiation and progression, along with chemotherapeutic resistance and ferroptotic cell death failure; however, the significance of mitochondria in various cancer types remains a matter of debate for the moment. The aim of this study is to ascertain the outcome of transferring healthy mitochondria into the aggressive and rapidly proliferating prostate cancer (PC-3) cells and afterwards evaluate the efficacy of combination therapy with or without the ferroptosis inducer erastin. In this sense, normal mitochondria were first isolated from human umbilical cord-derived mesenchymal stem cells, human umbilical vein endothelial cells, and human embryonic kidney cells and were later transferred into PC-3 cells and rhodamine 6G-treated PC-3 cells exhibiting mitochondrial dysfunction. Next, cell proliferation and sensitivity to cisplatin were measured using Cell Counting Kit-8 and the Malondialdehyde Assay Lipid Peroxidation Kit, respectively, along with ferroptotic damage. Transferring the healthy mitochondria into PC-3 cells was observed to increase cell proliferation and rescue the cisplatin-induced cell death, but not the erastin-induced ferroptosis, as in mitochondrial transfer effectively enhanced erastin-mediated ferroptosis in PC-3 cells. Hence, the introduction of healthy mitochondria into the highly aggressive and proliferating cancer cells would be deemed a brand new therapeutic strategy for a variety of cancers.

Ex vivo gene therapy for lysosomal storage disorders: future perspectives

INTRODUCTION

Lysosomal storage disorders (LSD) are a group of monogenic rare diseases caused by pathogenic variants in genes that encode proteins related to lysosomal function. These disorders are good candidates for gene therapy for different reasons: they are monogenic, most of lysosomal proteins are enzymes that can be secreted and cross-correct neighboring cells, and small quantities of these proteins are able to produce clinical benefits in many cases. Ex vivo gene therapy allows for autologous transplant of modified cells from different sources, including stem cells and hematopoietic precursors.

AREAS COVERED

Here, we summarize the main gene therapy and genome editing strategies that are currently being used as ex vivo gene therapy approaches for lysosomal disorders, highlighting important characteristics, such as vectors used, strategies, types of cells that are modified and main results in different disorders.

EXPERT OPINION

Clinical trials are already ongoing, and soon approved therapies for LSD based on ex vivo gene therapy approaches should reach the market.

In colon cancer cells fascin1 regulates adherens junction remodeling

Adherens junctions (AJs) are a defining feature of all epithelial cells. They regulate epithelial tissue architecture and integrity, and their dysregulation is a key step in tumor metastasis. AJ remodeling is crucial for cancer progression, and it plays a key role in tumor cell survival, growth, and dissemination. Few studies have examined AJ remodeling in cancer cells consequently, it remains poorly understood and unleveraged in the treatment of metastatic carcinomas. Fascin1 is an actin-bundling protein that is absent from the normal epithelium but its expression in colon cancer is linked to metastasis and increased mortality. Here, we provide the molecular mechanism of AJ remodeling in colon cancer cells and identify for the first time, fascin1's function in AJ remodeling. We show that in colon cancer cells fascin1 remodels junctional actin and actomyosin contractility which makes AJs less stable but more dynamic. By remodeling AJs fascin1 drives mechanoactivation of WNT/β-catenin signaling and generates "collective plasticity" which influences the behavior of cells during cell migration. The impact of mechanical inputs on WNT/β-catenin activation in cancer cells remains poorly understood. Our findings highlight the role of AJ remodeling and mechanosensitive WNT/β-catenin signaling in the growth and dissemination of colorectal carcinomas.

[Cystinosis: From the gene identification to the first gene therapy clinical trial]

Cystinosis is an autosomal recessive metabolic disease characterized by lysosomal accumulation of cystine in all the cells of the body. Infantile cystinosis begins in infancy by a renal Fanconi syndrome and eventually leads to multi-organ failure, including the kidney, eye, thyroid, muscle, and pancreas, eventually causing premature death in early adulthood. The current treatment is the drug cysteamine that only delays the progression of the disease. We identified the gene involved, CTNS, and showed that the encoded protein, cystinosin, is a proton-driven cystine transporter. We generated a mouse model of cystinosis, the Ctns-/- mice, that recapitulates the main disease complications. The goal was next to develop a gene therapy approach for cystinosis. We used bone marrow stem cells as a vehicle to bring the healthy CTNS gene to tissues, and we showed that wild-type hematopoietic stem and progenitor cell (HSPC) transplantation led to abundant tissue integration of bone marrow-derived cells, significant decrease of tissue cystine accumulation and long-term kidney, eye and thyroid preservation. We then developed an autologous transplantation approach of HSPCs modified ex vivo using a lentiviral vector to introduce a functional CTNS cDNA, and showed its efficacy in Ctns-/- mice. We conducted the pharmacology/toxicology studies, developed the manufacturing process using human CD34+ cells, and design the clinical trial. We received Food and Drug Administration (FDA)-clearance to start a phase 1/2 clinical trial for cystinosis in December 2018. Six patients have been treated so far. In this review, we describe the path to go from the gene to a gene therapy approach for cystinosis.

Macrophages Promote Tumor Cell Extravasation across an Endothelial Barrier through Thin Membranous Connections

Macrophages are important players involved in the progression of breast cancer, including in seeding the metastatic niche. However, the mechanism by which macrophages in the lung parenchyma interact with tumor cells in the vasculature to promote tumor cell extravasation at metastatic sites is not clear. To mimic macrophage-driven tumor cell extravasation, we used an in vitro assay (eTEM) in which an endothelial monolayer and a matrigel-coated filter separated tumor cells and macrophages from each other. The presence of macrophages promoted tumor cell extravasation while macrophage conditioned media was insufficient to stimulate tumor cell extravasation in vitro . This finding is consistent with a requirement for direct contact between macrophages and tumor cells. We observed the presence of Thin Membranous Connections (TMCs) resembling similar structures formed between macrophages and tumor cells called tunneling nanotubes which we previously demonstrated to be important in tumor cell invasion in vitro and in vivo (Hanna 2019). To determine if TMCs are important for tumor cell extravasation, we used macrophages with reduced levels of endogenous M-Sec (TNFAIP2), which causes a defect in tunneling nanotube formation. As predicted, these macrophages showed reduced macrophage-tumor cell TMCs. In both, human and murine breast cancer cell lines, there was also a concomitant reduction in tumor cell extravasation in vitro when co-cultured with M-Sec deficient macrophages compared to control macrophages. We also detected TMCs formed between macrophages and tumor cells through the endothelial layer in the eTEM assay. Furthermore, tumor cells were more frequently found in pores under the endothelium that contain macrophage protrusions. To determine the role of macrophage-tumor cell TMCs in vivo , we generated an M-Sec deficient mouse. Using an in vivo model of experimental metastasis, we detected a significant reduction in the number of metastatic lesions in M-Sec deficient mice compared to wild type mice. There was no difference in the size of the metastases, consistent with a defect specific to tumor cell extravasation and not metastatic outgrowth. Additionally, examination of time-lapse intravital-imaging (IVI) data sets of breast cancer cell extravasation in the lung, we could detect the presence of TMCs between extravascular macrophages and vascular tumor cells. Overall, our data indicate that macrophage TMCs play an important role in promoting the extravasation of circulating tumor cells in the lung.

Protective effect of the tunneling nanotube-TNFAIP2/M-sec system on podocyte autophagy in diabetic nephropathy

Podocyte injury leading to albuminuria is a characteristic feature of diabetic nephropathy (DN). Hyperglycemia and advanced glycation end products (AGEs) are major determinants of DN. However, the underlying mechanisms of podocyte injury remain poorly understood. The cytosolic protein TNFAIP2/M-Sec is required for tunneling nanotubes (TNTs) formation, which are membrane channels that transiently connect cells, allowing organelle transfer. Podocytes express TNFAIP2 and form TNTs, but the potential relevance of the TNFAIP2-TNT system in DN is unknown. We studied TNFAIP2 expression in both human and experimental DN and the renal effect of tnfaip2 deletion in streptozotocin-induced DN. Moreover, we explored the role of the TNFAIP2-TNT system in podocytes exposed to diabetes-related insults. TNFAIP2 was overexpressed by podocytes in both human and experimental DN and exposre of podocytes to high glucose and AGEs induced the TNFAIP2-TNT system. In diabetic mice, tnfaip2 deletion exacerbated albuminuria, renal function loss, podocyte injury, and mesangial expansion. Moreover, blockade of the autophagic flux due to lysosomal dysfunction was observed in diabetes-injured podocytes both in vitro and in vivo and exacerbated by tnfaip2 deletion. TNTs allowed autophagosome and lysosome exchange between podocytes, thereby ameliorating AGE-induced lysosomal dysfunction and apoptosis. This protective effect was abolished by tnfaip2 deletion, TNT inhibition, and donor cell lysosome damage. By contrast, Tnfaip2 overexpression enhanced TNT-mediated transfer and prevented AGE-induced autophagy and lysosome dysfunction and apoptosis. In conclusion, TNFAIP2 plays an important protective role in podocytes in the context of DN by allowing TNT-mediated autophagosome and lysosome exchange and may represent a novel druggable target.Abbreviations: AGEs: advanced glycation end products; AKT1: AKT serine/threonine kinase 1; AO: acridine orange; ALs: autolysosomes; APs: autophagosomes; BM: bone marrow; BSA: bovine serum albumin; CTSD: cathepsin D; DIC: differential interference contrast; DN: diabetic nephropathy; FSGS: focal segmental glomerulosclerosis; HG: high glucose; KO: knockout; LAMP1: lysosomal-associated membrane protein 1; LMP: lysosomal membrane permeabilization; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; PI3K: phosphoinositide 3-kinase; STZ: streptozotocin; TNF: tumor necrosis factor; TNFAIP2: tumor necrosis factor, alpha-induced protein 2; TNTs: tunneling nanotubes; WT: wild type.

Hematopoietic stem and progenitors cells gene editing: Beyond blood disorders

Lessons learned from decades-long practice in the transplantation of hematopoietic stem and progenitor cells (HSPCs) to treat severe inherited disorders or cancer, have set the stage for the current ex vivo gene therapies using autologous gene-modified hematopoietic stem and progenitor cells that have treated so far, hundreds of patients with monogenic disorders. With increased knowledge of hematopoietic stem and progenitor cell biology, improved modalities for patient conditioning and with the emergence of new gene editing technologies, a new era of hematopoietic stem and progenitor cell-based gene therapies is poised to emerge. Gene editing has the potential to restore physiological expression of a mutated gene, or to insert a functional gene in a precise locus with reduced off-target activity and toxicity. Advances in patient conditioning has reduced treatment toxicities and may improve the engraftment of gene-modified cells and specific progeny. Thanks to these improvements, new potential treatments of various blood- or immune disorders as well as other inherited diseases will continue to emerge. In the present review, the most recent advances in hematopoietic stem and progenitor cell gene editing will be reported, with a focus on how this approach could be a promising solution to treat non-blood-related inherited disorders and the mechanisms behind the therapeutic actions discussed.

TNTdetect.AI: A Deep Learning Model for Automated Detection and Counting of Tunneling Nanotubes in Microscopy Images

BACKGROUND

Tunneling nanotubes (TNTs) are cellular structures connecting cell membranes and mediating intercellular communication. TNTs are manually identified and counted by a trained investigator; however, this process is time-intensive. We therefore sought to develop an automated approach for quantitative analysis of TNTs.

METHODS

We used a convolutional neural network (U-Net) deep learning model to segment phase contrast microscopy images of both cancer and non-cancer cells. Our method was composed of preprocessing and model development. We developed a new preprocessing method to label TNTs on a pixel-wise basis. Two sequential models were employed to detect TNTs. First, we identified the regions of images with TNTs by implementing a classification algorithm. Second, we fed parts of the image classified as TNT-containing into a modified U-Net model to estimate TNTs on a pixel-wise basis.

RESULTS

The algorithm detected 49.9% of human expert-identified TNTs, counted TNTs, and calculated the number of TNTs per cell, or TNT-to-cell ratio (TCR); it detected TNTs that were not originally detected by the experts. The model had 0.41 precision, 0.26 recall, and 0.32 f-1 score on a test dataset. The predicted and true TCRs were not significantly different across the training and test datasets (p = 0.78).

CONCLUSIONS

Our automated approach labeled and detected TNTs and cells imaged in culture, resulting in comparable TCRs to those determined by human experts. Future studies will aim to improve on the accuracy, precision, and recall of the algorithm.

Cystinosin deficient rats recapitulate the phenotype of nephropathic cystinosis

The lysosomal storage disease cystinosis is caused by mutations in CTNS, encoding a cystine transporter, and in its severest form leads to proximal tubule dysfunction followed by kidney failure. Patients receive the drug-based therapy cysteamine from diagnosis. However, despite long-term treatment, cysteamine only slows the progression of end-stage renal disease. Pre-clinical testing in cystinotic rodents is required to evaluate new therapies; however, the current models are sub-optimal. To solve this problem we generated a new cystinotic rat model using CRISPR/Cas9-mediated gene editing to disrupt exon 3 of Ctns and measured various parameters over a 12-month time-course. Ctns^-/- rats display hallmarks of cystinosis by 3-6 months of age as seen by a failure to thrive, excessive thirst and urination, cystine accumulation in tissues, corneal cystine crystals, a loss of Lrp2 in proximal tubules and immune cell infiltration. High levels of glucose, calcium, albumin and protein are excreted at 6-months of age, consistent with the onset of Fanconi syndrome, with a progressive diminution of urine urea and creatinine from 9-months of age, indicative of chronic kidney disease. The kidney histology and immunohistochemistry showed proximal tubule atrophy and glomerular damage as well as classic 'swan neck' lesions. Overall, Ctns^-/- rats show a disease progression that more faithfully recapitulates nephropathic cystinosis than existing rodent models. The Ctns^-/- rat provides an excellent new rodent model of nephropathic cystinosis that is ideally suited for conducting pre-clinical drug testing and a powerful tool to advance cystinosis research.

Advantages and Limitations of Gene Therapy and Gene Editing for Friedreich's Ataxia

Friedreich's ataxia (FRDA) is an inherited, multisystemic disorder predominantly caused by GAA hyper expansion in intron 1 of frataxin (FXN) gene. This expansion mutation transcriptionally represses FXN, a mitochondrial protein that is required for iron metabolism and mitochondrial homeostasis, leading to neurodegerative and cardiac dysfunction. Current therapeutic options for FRDA are focused on improving mitochondrial function and increasing frataxin expression through pharmacological interventions but are not effective in delaying or preventing the neurodegeneration in clinical trials. Recent research on in vivo and ex vivo gene therapy methods in FRDA animal and cell models showcase its promise as a one-time therapy for FRDA. In this review, we provide an overview on the current and emerging prospects of gene therapy for FRDA, with specific focus on advantages of CRISPR/Cas9-mediated gene editing of FXN as a viable option to restore endogenous frataxin expression. We also assess the potential of ex vivo gene editing in hematopoietic stem and progenitor cells as a potential autologous transplantation therapeutic option and discuss its advantages in tackling FRDA-specific safety aspects for clinical translation.

Tunneling Nanotubes between Cells Migrating in ECM Mimicking Fibrous Environments

Simple Summary

Tumor cells grow, spread, and invade in a three-dimensional manner, but most experimental approaches in cancer cell biology focus on the behavior of cells in two-dimensional spaces. Patterns of cell invasion and spread in 2D may not accurately depict cell behavior in 3D tumors. We cultivated and investigated malignant mesothelioma cells on a 3D scaffold composed of nanofibers positioned in parallel and crosshatched network configurations to overcome this barrier. We focused on studying long extensions called tunneling nanotubes (TNTs) protruding from cells and connecting with other cells, which have been shown to transmit signals from cell to cell and extend into the tumor microenvironments in a 3D manner. This manuscript describes the biophysics of the formation and function of cancer cell TNTs. These findings will impact the research community by accurately assessing how TNTs affect cancer cell invasion and migration in their natural 3D microenvironment using a novel bioengineered platform.

Abstract

Tunneling nanotubes (TNTs) comprise a unique class of actin-rich nanoscale membranous protrusions. They enable long-distance intercellular communication and may play an integral role in tumor formation, progression, and drug resistance. TNTs are three-dimensional, but nearly all studies have investigated them using two-dimensional cell culture models. Here, we applied a unique 3D culture platform consisting of crosshatched and aligned fibers to fabricate synthetic suspended scaffolds that mimic the native fibrillar architecture of tumoral extracellular matrix (ECM) to characterize TNT formation and function in its native state. TNTs are upregulated in malignant mesothelioma; we used this model to analyze the biophysical properties of TNTs in this 3D setting, including cell migration in relation to TNT dynamics, rate of TNT-mediated intercellular transport of cargo, and conformation of TNT-forming cells. We found that highly migratory elongated cells on aligned fibers formed significantly longer but fewer TNTs than uniformly spread cells on crossing fibers. We developed new quantitative metrics for the classification of TNT morphologies based on shape and cytoskeletal content using confocal microscopy. In sum, our strategy for culturing cells in ECM-mimicking bioengineered scaffolds provides a new approach for accurate biophysical and biologic assessment of TNT formation and structure in native fibrous microenvironments.

Development of a fibrin-mediated gene delivery system for the treatment of cystinosis via design of experiment

Cystinosis is a rare disease, caused by a mutation in the gene cystinosin and characterised by the accumulation of cystine crystals. Advantages of biomaterial-mediated gene delivery include reduced safety concerns and the possibility to cure organs that are difficult to treat using systemic gene transfer methods. This study developed novel fibrin hydrogels for controlled, localised gene delivery, for the treatment of cystinosis. In the first part, fabrication parameters (i.e., DNA, thrombin, and aprotinin concentrations) were optimised, using a Design of Experiment (DOE) methodology. DOE is a statistical engineering approach to process optimisation, which increases experimental efficiency, reduces the number of experiments, takes into consideration interactions between different parameters, and allows the creation of predictive models. This study demonstrated the utility of DOE to the development of gene delivery constructs. In the second part of the study, primary fibroblasts from a patient with cystinosis were seeded on the biomaterials. Seeded cells expressed the recombinant CTNS and showed a decrease in cystine content. Furthermore, conditioned media contained functional copies of the recombinant CTNS. These were taken up by monolayer cultures of non-transfected cells. This study described a methodology to develop gene delivery constructs by using a DOE approach and ultimately provided new insights into the treatment of cystinosis.

In Vitro and In Vivo Models to Study Nephropathic Cystinosis

The development over the past 50 years of a variety of cell lines and animal models has provided valuable tools to understand the pathophysiology of nephropathic cystinosis. Primary cultures from patient biopsies have been instrumental in determining the primary cause of cystine accumulation in the lysosomes. Immortalised cell lines have been established using different gene constructs and have revealed a wealth of knowledge concerning the molecular mechanisms that underlie cystinosis. More recently, the generation of induced pluripotent stem cells, kidney organoids and tubuloids have helped bridge the gap between in vitro and in vivo model systems. The development of genetically modified mice and rats have made it possible to explore the cystinotic phenotype in an in vivo setting. All of these models have helped shape our understanding of cystinosis and have led to the conclusion that cystine accumulation is not the only pathology that needs targeting in this multisystemic disease. This review provides an overview of the in vitro and in vivo models available to study cystinosis, how well they recapitulate the disease phenotype, and their limitations.

Deficiency of the sedoheptulose kinase (Shpk) does not alter the ability of hematopoietic stem cells to rescue cystinosis in the mouse model

Cystinosis is an autosomal recessive lysosomal storage disorder caused by mutations in the CTNS gene encoding the lysosomal cystine transporter, cystinosin, and leading to multi-organ degeneration including kidney failure. A clinical trial for cystinosis is ongoing to test the safety and efficacy of transplantation of autologous hematopoietic stem and progenitor cells (HSPCs) ex vivo gene-modified to introduce functional CTNS cDNA. Preclinical studies in Ctns-/- mice previously showed that a single HSPC transplantation led to significant tissue cystine decrease and long-term tissue preservation. The main mechanism of action involves the differentiation of the transplanted HSPCs into macrophages within tissues and transfer of cystinosin-bearing lysosomes to the diseased cells via tunneling nanotubes. However, a major concern was that the most common cystinosis-causing mutation in humans is a 57-kb deletion that eliminates not only CTNS but also the adjacent sedopheptulose kinase SHPK/CARKL gene encoding a metabolic enzyme that influences macrophage polarization. Here, we investigated if absence of Shpk could negatively impact the efficiency of transplanted HSPCs to differentiate into macrophages within tissues and then to prevent cystinosis rescue. We generated Shpk knockout mouse models and detected a phenotype consisting of perturbations in the pentose phosphate pathway (PPP), the metabolic shunt regulated by SHPK. Shpk-/- mice also recapitulated the urinary excretion of sedoheptulose and erythritol found in cystinosis patients homozygous for the 57-kb deletion. Transplantation of Shpk-/--HSPCs into Ctns-/- mice resulted in significant reduction in tissue cystine load and restoration of Ctns expression, as well as improved kidney architecture comparable to WT-HSPC recipients. Altogether, these data demonstrate that absence of SHPK does not alter the ability of HSPCs to rescue cystinosis, and then patients homozygous for the 57-kb deletion should benefit from ex vivo gene therapy and can be enrolled in the ongoing clinical trial. However, because of the limits inherent to animal models, outcomes of this patient population will be carefully compared to the other enrolled subjects.

Hematopoietic Stem Cell Gene Therapy for Cystinosis: From Bench-to-Bedside

Cystinosis is an autosomal recessive metabolic disease that belongs to the family of lysosomal storage disorders. The gene involved is the CTNS gene that encodes cystinosin, a seven-transmembrane domain lysosomal protein, which is a proton-driven cystine transporter. Cystinosis is characterized by the lysosomal accumulation of cystine, a dimer of cysteine, in all the cells of the body leading to multi-organ failure, including the failure of the kidney, eye, thyroid, muscle, and pancreas, and eventually causing premature death in early adulthood. The current treatment is the drug cysteamine, which is onerous and expensive, and only delays the progression of the disease. Employing the mouse model of cystinosis, using Ctns-/- mice, we first showed that the transplantation of syngeneic wild-type murine hematopoietic stem and progenitor cells (HSPCs) led to abundant tissue integration of bone marrow-derived cells, a significant decrease in tissue cystine accumulation, and long-term kidney, eye and thyroid preservation. To translate this result to a potential human therapeutic treatment, given the risks of mortality and morbidity associated with allogeneic HSPC transplantation, we developed an autologous transplantation approach of HSPCs modified ex vivo using a self-inactivated lentiviral vector to introduce a functional version of the CTNS cDNA, pCCL-CTNS, and showed its efficacy in Ctns-/- mice. Based on these promising results, we held a pre-IND meeting with the Food and Drug Administration (FDA) to carry out the FDA agreed-upon pharmacological and toxicological studies for our therapeutic candidate, manufacturing development, production of the GMP lentiviral vector, design Phase 1/2 of the clinical trial, and filing of an IND application. Our IND was cleared by the FDA on 19 December 2018, to proceed to the clinical trial using CD34+ HSPCs from the G-CSF/plerixafor-mobilized peripheral blood stem cells of patients with cystinosis, modified by ex vivo transduction using the pCCL-CTNS vector (investigational product name: CTNS-RD-04). The clinical trial evaluated the safety and efficacy of CTNS-RD-04 and takes place at the University of California, San Diego (UCSD) and will include up to six patients affected with cystinosis. Following leukapheresis and cell manufacturing, the subjects undergo myeloablation before HSPC infusion. Patients also undergo comprehensive assessments before and after treatment to evaluate the impact of CTNS-RD-04 on the clinical outcomes and cystine and cystine crystal levels in the blood and tissues for 2 years. If successful, this treatment could be a one-time therapy that may eliminate or reduce renal deterioration as well as the long-term complications associated with cystinosis. In this review, we will describe the long path from bench-to-bedside for autologous HSPC gene therapy used to treat cystinosis.

Rab11a mediates cell-cell spread and reassortment of influenza A virus genomes via tunneling nanotubes

Influenza A virus [IAV] genomes comprise eight negative strand RNAs packaged into virions in the form of viral ribonucleoproteins [vRNPs]. Rab11a plays a crucial role in the transport of vRNPs from the nucleus to the plasma membrane via microtubules, allowing assembly and virus production. Here, we identify a novel function for Rab11a in the inter-cellular transport of IAV vRNPs using tunneling nanotubes [TNTs]as molecular highways. TNTs are F-Actin rich tubules that link the cytoplasm of nearby cells. In IAV-infected cells, Rab11a was visualized together with vRNPs in these actin-rich intercellular connections. To better examine viral spread via TNTs, we devised an infection system in which conventional, virion-mediated, spread was not possible. Namely, we generated HA-deficient reporter viruses which are unable to produce progeny virions but whose genomes can be replicated and trafficked. In this system, vRNP transfer to neighboring cells was observed and this transfer was found to be dependent on both actin and Rab11a. Generation of infectious virus via TNT transfer was confirmed using donor cells infected with HA-deficient virus and recipient cells stably expressing HA protein. Mixing donor cells infected with genetically distinct IAVs furthermore revealed the potential for Rab11a and TNTs to serve as a conduit for genome mixing and reassortment in IAV infections. These data therefore reveal a novel role for Rab11a in the IAV life cycle, which could have significant implications for within-host spread, genome reassortment and immune evasion.

Clinical Development of Cell Therapies to Halt Lysosomal Storage Diseases: Results and Lessons Learned

Although cross-correction was discovered more than 50 years ago, and held the promise of drastically improving disease management, still no cure exists for lysosomal storage diseases (LSDs). Cell therapies hold the potential to halt disease progression: either a subset of autologous cells can be ex vivo/ in vivo transfected with the functional gene or allogenic wild type stem cells can be transplanted. However, majority of cell-based attempts have been ineffective, due to the difficulties in reversing neuronal symptomatology, in finding appropriate gene transfection approaches, in inducing immune tolerance, reducing the risk of graft versus host disease (GVHD) when allogenic cells are used and that of immune response when engineered viruses are administered, coupled with a limited secretion and uptake of some enzymes. In the last decade, due to advances in our understanding of lysosomal biology and mechanisms of cross-correction, coupled with progresses in gene therapy, ongoing pre-clinical and clinical investigations have remarkably increased. Even gene editing approaches are currently under clinical experimentation. This review proposes to critically discuss and compare trends and advances in cell-based and gene therapy for LSDs. Systemic gene delivery and transplantation of allogenic stem cells will be initially discussed, whereas proposed brain targeting methods will be then critically outlined.

α-Synuclein fibrils subvert lysosome structure and function for the propagation of protein misfolding between cells through tunneling nanotubes

The accumulation of α-synuclein (α-syn) aggregates in specific brain regions is a hallmark of synucleinopathies including Parkinson disease (PD). α-Syn aggregates propagate in a "prion-like" manner and can be transferred inside lysosomes to recipient cells through tunneling nanotubes (TNTs). However, how lysosomes participate in the spreading of α-syn aggregates is unclear. Here, by using super-resolution (SR) and electron microscopy (EM), we find that α-syn fibrils affect the morphology of lysosomes and impair their function in neuronal cells. In addition, we demonstrate that α-syn fibrils induce peripheral redistribution of lysosomes, likely mediated by transcription factor EB (TFEB), increasing the efficiency of α-syn fibrils' transfer to neighboring cells. We also show that lysosomal membrane permeabilization (LMP) allows the seeding of soluble α-syn in cells that have taken up α-syn fibrils from the culture medium, and, more importantly, in healthy cells in coculture, following lysosome-mediated transfer of the fibrils. Moreover, we demonstrate that seeding occurs mainly at lysosomes in both donor and acceptor cells, after uptake of α-syn fibrils from the medium and following their transfer, respectively. Finally, by using a heterotypic coculture system, we determine the origin and nature of the lysosomes transferred between cells, and we show that donor cells bearing α-syn fibrils transfer damaged lysosomes to acceptor cells, while also receiving healthy lysosomes from them. These findings thus contribute to the elucidation of the mechanism by which α-syn fibrils spread through TNTs, while also revealing the crucial role of lysosomes, working as a Trojan horse for both seeding and propagation of disease pathology.

Role of Tunneling Nanotubes in Viral Infection, Neurodegenerative Disease, and Cancer

The network of tunneling nanotubes (TNTs) represents the filamentous (F)-actin rich tubular structure which is connected to the cytoplasm of the adjacent and or distant cells to mediate efficient cell-to-cell communication. They are long cytoplasmic bridges with an extraordinary ability to perform diverse array of function ranging from maintaining cellular physiology and cell survival to promoting immune surveillance. Ironically, TNTs are now widely documented to promote the spread of various pathogens including viruses either during early or late phase of their lifecycle. In addition, TNTs have also been associated with multiple pathologies in a complex multicellular environment. While the recent work from multiple laboratories has elucidated the role of TNTs in cellular communication and maintenance of homeostasis, this review focuses on their exploitation by the diverse group of viruses such as retroviruses, herpesviruses, influenza A, human metapneumovirus and SARS CoV-2 to promote viral entry, virus trafficking and cell-to-cell spread. The later process may aggravate disease severity and the associated complications due to widespread dissemination of the viruses to multiple organ system as observed in current coronavirus disease 2019 (COVID-19) patients. In addition, the TNT-mediated intracellular spread can be protective to the viruses from the circulating immune surveillance and possible neutralization activity present in the extracellular matrix. This review further highlights the relevance of TNTs in ocular and cardiac tissues including neurodegenerative diseases, chemotherapeutic resistance, and cancer pathogenesis. Taken together, we suggest that effective therapies should consider precise targeting of TNTs in several diseases including virus infections.

Molecular Mechanisms and Treatment Options of Nephropathic Cystinosis

Nephropathic cystinosis is a severe, monogenic systemic disorder that presents early in life and leads to progressive organ damage, particularly affecting the kidneys. It is caused by mutations in the CTNS gene, which encodes the lysosomal transporter cystinosin, resulting in intralysosomal accumulation of cystine. Recent studies demonstrated that the loss of cystinosin is associated with disrupted autophagy dynamics, accumulation of distorted mitochondria, and increased oxidative stress, leading to abnormal proliferation and dysfunction of kidney cells. We discuss these molecular mechanisms driving nephropathic cystinosis. Further, we consider how unravelling molecular mechanisms supports the identification and development of new strategies for cystinosis by the use of small molecules, biologicals, and genetic rescue of the disease in vitro and in vivo.

Umbilical mesenchymal stem cell-derived extracellular vesicles as enzyme delivery vehicle to treat Morquio A fibroblasts

BACKGROUND

Mucopolysaccharidosis IVA (Morquio A syndrome) is a lysosomal storage disease caused by the deficiency of enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS), which results in the accumulation of the glycosaminoglycans (GAGs), keratan sulfate, and chondroitin-6-sulfate in the lysosomes of all tissues causing systemic dysfunction. Current treatments include enzyme replacement therapy (ERT) which can treat only certain aspects of the disease such as endurance-related biological endpoints. A key challenge in ERT is ineffective enzyme uptake in avascular tissues, which makes the treatment of the corneal, cartilage, and heart valvular tissue difficult. The aim of this study was to culture human umbilical mesenchymal stem cells (UMSC), demonstrate presence of GALNS enzyme activity within the extracellular vesicles (EVs) derived from these UMSC, and study how these secreted EVs are taken up by GALNS-deficient cells and used by the deficient cell's lysosomes.

METHODS

We obtained and cultured UMSC from the umbilical cord tissue from anonymous donors from the Saint Louis Cord Blood Bank. We characterized UMSC cell surface markers to confirm phenotype by cell sorting analyses. In addition, we confirmed that UMSC secrete GALNS enzyme creating conditioned media for co-culture experiments with GALNS deficient cells. Lastly, we isolated EVs derived from UMSC by ultracentrifugation to confirm source of GALNS enzyme.

RESULTS

Co-culture and confocal microscopy experiments indicated that the lysosomal content from UMSC migrated to deficient cells as evidenced by the peak signal intensity occurring at 15 min. EVs released by UMSC were characterized indicating that the EVs contained the active GALNS enzyme. Uptake of GALNS within EVs by deficient fibroblasts was not affected by mannose-6-phosphate (M6P) inhibition, suggesting that EV uptake by these fibroblasts is gradual and might be mediated by a different means than the M6P receptor.

CONCLUSIONS

UMSC can deliver EVs containing functional GALNS enzyme to deficient cells. This enzyme delivery method, which was unaffected by M6P inhibition, can function as a novel technique for reducing GAG accumulation in cells in avascular tissues, thereby providing a potential treatment option for Morquio A syndrome.

The Role of Exosomes in Lysosomal Storage Disorders

Exosomes, small membrane-bound organelles formed from endosomal membranes, represent a heterogenous source of biological and pathological biomarkers capturing the metabolic status of a cell. Exosomal cargo, including lipids, proteins, mRNAs, and miRNAs, can either act as inter-cellular messengers or are shuttled for autophagic/lysosomal degradation. Most cell types in the central nervous system (CNS) release exosomes, which serve as long and short distance communicators between neurons, astrocytes, oligodendrocytes, and microglia. Lysosomal storage disorders are diseases characterized by the accumulation of partially or undigested cellular waste. The exosomal content in these diseases is intrinsic to each individual disorder. Emerging research indicates that lysosomal dysfunction enhances exocytosis, and hence, in lysosomal disorders, exosomal secretion may play a role in disease pathogenesis. Furthermore, the unique properties of exosomes and their ability to carry cargo between adjacent cells and organs, and across the blood-brain barrier, make them attractive candidates for use as therapeutic delivery vehicles. Thus, understanding exosomal content and function may have utility in the treatment of specific lysosomal storage disorders. Since lysosomal dysfunction and the deficiency of at least one lysosomal enzyme, glucocerebrosidase, is associated with the development of parkinsonism, the study and use of exosomes may contribute to an improved understanding of Parkinson disease, potentially leading to new therapeutics.

Peering into tunneling nanotubes-The path forward

The identification of Tunneling Nanotubes (TNTs) and TNT-like structures signified a critical turning point in the field of cell-cell communication. With hypothesized roles in development and disease progression, TNTs' ability to transport biological cargo between distant cells has elevated these structures to a unique and privileged position among other mechanisms of intercellular communication. However, the field faces numerous challenges-some of the most pressing issues being the demonstration of TNTs in vivo and understanding how they form and function. Another stumbling block is represented by the vast disparity in structures classified as TNTs. In order to address this ambiguity, we propose a clear nomenclature and provide a comprehensive overview of the existing knowledge concerning TNTs. We also discuss their structure, formation-related pathways, biological function, as well as their proposed role in disease. Furthermore, we pinpoint gaps and dichotomies found across the field and highlight unexplored research avenues. Lastly, we review the methods employed to date and suggest the application of new technologies to better understand these elusive biological structures.

Opportunities and Challenges in Tunneling Nanotubes Research: How Far from Clinical Application?

Tunneling nanotubes (TNTs) are recognized long membrane nanotubes connecting distance cells. In the last decade, growing evidence has shown that these subcellular structures mediate the specific transfer of cellular materials, pathogens, and electrical signals between cells. As intercellular bridges, they play a unique role in embryonic development, collective cell migration, injured cell recovery, cancer treatment resistance, and pathogen propagation. Although TNTs have been considered as potential drug targets for treatment, there is still a long way to go to translate the research findings into clinical practice. Herein, we emphasize the heterogeneous nature of TNTs by systemically summarizing the current knowledge on their morphology, structure, and biogenesis in different types of cells. Furthermore, we address the communication efficiency and biological outcomes of TNT-dependent transport related to diseases. Finally, we discuss the opportunities and challenges of TNTs as an exciting therapeutic approach by focusing on the development of efficient and safe drugs targeting TNTs.

Pathogenic Stress Induces Human Monocyte to Express an Extracellular Web of Tunneling Nanotubes

Actin-based tunneling nanotubes are a means of intercellular communication between remote cells. In the last decade, this type of nanotube was described in a wide variety of cell types and it became widely accepted that communication through these nanotubes is related to response to environmental changes. Few reports, however, are available regarding the expression of similar nanotubes in vivo or in primary cells. Moreover, the functional significance of this intercellular communication for health and disease is largely unknown. In this context, and as a first step in unraveling these questions, we examined the formation of similar nanotubes in primary peripheral human monocytes. To that end, we combined the use of a live cell imaging system along with advanced methods of fluorescent and scanning electron microscopy. This experimental approach reveals for the first time that the bacterial lipopolysaccharide endotoxin induces a transient expression of an unexpected abundance of actin-based tunneling nanotubes associated with vesicles. In addition, it was found that a similar response can be achieved by treating human monocytes with various bacterial and yeast membrane components, as well as with a viral component analog. In all these cases, this response is mediated by distinct complexes of toll-like receptors. Therefore, we suggest that the observed phenomena are related to a broad type of monocyte pathogen response, and raise the possibility that the phenomena described above may be involved in many clinical situations related to inflammation as a new topic of study.

Immune Cell Connection by Tunneling Nanotubes: The Impact of Intercellular Cross-Talk on the Immune Response and Its Therapeutic Applications

Direct intercellular communication is an important prerequisite for the development of multicellular organisms, the regeneration of tissue, and the maintenance of various physiological activities. Tunnel nanotubes (TNTs), which have diameters of approximately 50-1500 nm and lengths of up to several cell diameters, can connect cells over long distances and have emerged as one of the most important recently discovered types of efficient communication between cells. Moreover, TNTs can also directly transfer organelles, vehicles, proteins, genetic material, ions, and small molecules from one cell to adjacent and even distant cells. However, the mechanism of intercellular communication between various immune cells within the complex immune system has not been fully elucidated. Studies in the past decades have confirmed the existence of TNTs in many types of cells, especially in various kinds of immune cells. TNTs display different structural and functional characteristics between and within different immunocytes, playing a major role in the transmission of signals across various kinds of immune cells. In this review, we introduce the discovery and structure of TNTs, as well as their different functional properties within different immune cells. We also discuss the roles of TNTs in potentiating the immune response and their potential therapeutic applications.

Brain cell type-specific endocytosis of arylsulfatase A identifies limitations of enzyme-based therapies for metachromatic leukodystrophy

Enzyme replacement therapies, allogeneic bone marrow transplantation and gene therapies are treatment options for lysosomal storage diseases caused by inherited deficiencies of soluble lysosomal enzymes. Independent from the approach, the enzyme must be delivered to lysosomes of deficient patient cells. Little is known about the dissemination of enzyme within a tissue where cells compete for uptake via different receptor systems, binding affinities and endocytic rates. To evaluate dissemination and lysosomal targeting of a lysosomal enzyme in the CNS, we analysed receptor-mediated endocytosis of arylsulfatase A (ASA) by different types of brain-derived cell lines and primary murine brain cells. For ASA expressed by chinese hamster ovary cells for enzyme replacement therapy of metachromatic leukodystrophy, endocytic rates decline from microglia to neurons and astrocytes and to oligodendrocytes. Only immature oligodendrocytes endocytose significant amounts of enzyme. Uptake by non-microglial cells is due to mannose 6-phosphate receptors, whereas several receptor systems participate in endocytosis by microglial cells. Interestingly, ASA expressed by microglial cells cannot be taken up in a mannose 6-phosphate dependent manner. The resulting failure to correct non-microglial cells corroborates in vivo data and indicates that therapeutic effects of allogeneic bone marrow transplantation and hematopoietic stem cell gene therapy on metachromatic leukodystrophy are independent of metabolic cross-correction of neurons, astrocytes and oligodendrocytes by receptor-mediated endocytosis.

Super-resolution imaging of the dynamic cleavage of intercellular tunneling nanotubes

As a new method of cell-cell communication, tunneling nanotubes (TNTs) play important roles in cell-cell signaling and mass exchanges. However, a lack of powerful tools to visualize dynamic TNTs with high temporal/spatial resolution restricts the exploration of their formation and cleavage, hindering the complete understanding of its mechanism. Herein, we present the first example of using stochastic optical reconstruction microscopy (STORM) to observe the tube-like structures of TNTs linking live cells with an easily prepared fluorescent dye. Because of this new imaging microscopy, the cleavage process of TNTs was observed with a high spatial resolution.

A Ticket to Ride: The Implications of Direct Intercellular Communication via Tunneling Nanotubes in Peritoneal and Other Invasive Malignancies

It is well established that the role of the tumor microenvironment (TME) in cancer progression and therapeutic resistance is crucial, but many of the underlying mechanisms are still being elucidated. Even with better understanding of molecular oncology and identification of genomic drivers of these processes, there has been a relative lag in identifying and appreciating the cellular drivers of both invasion and resistance. Intercellular communication is a vital process that unifies and synchronizes the diverse components of the tumoral infrastructure. Elucidation of the role of extracellular vesicles (EVs) over the past decade has cast a brighter light on this field. And yet even with this advance, in addition to diffusible soluble factor-mediated paracrine and endocrine cell communication as well as EVs, additional niches of intratumoral communication are filled by other modes of intercellular transfer. Tunneling nanotubes (TNTs), tumor microtubes (TMs), and other similar intercellular channels are long filamentous actin-based cellular conduits (in most epithelial cancer cell types, ~15-500 µm in length; 50–1000+ nm in width). They extend and form direct connections between distant cells, serving as conduits for direct intercellular transfer of cell cargo, such as mitochondria, exosomes, and microRNAs; however, many of their functional roles in mediating tumor growth remain unknown. These conduits literally create a physical bridge to create a syncytial network of dispersed cells amidst the intercellular stroma-rich matrix. Emerging evidence suggests that they provide a cellular mechanism for induction and emergence of drug resistance and contribute to increased invasive and metastatic potential. They have been imaged in vitro and also in vivo and ex vivo in tumors from human patients as well as animal models, thus not only proving their existence in the TME, but opening further speculation about their exact role in the dynamic niche of tumor ecosystems. TNT cellular networks are upregulated between cancer and stromal cells under hypoxic and other conditions of physiologic and metabolic stress. Furthermore, they can connect malignant cells to benign cells, including vascular endothelial cells. The field of investigation of TNT-mediated tumor-stromal, and tumor-tumor, cell-cell communication is gaining momentum. The mixture of conditions in the microenvironment exemplified by hypoxia-induced ovarian cancer TNTs playing a crucial role in tumor growth, as just one example, is a potential avenue of investigation that will uncover their role in relation to other known factors, including EVs. If the role of cancer heterocellular signaling via TNTs in the TME is proven to be crucial, then disrupting formation and maintenance of TNTs represents a novel therapeutic approach for ovarian and other similarly invasive peritoneal cancers.

Improving Molecular Therapy in the Kidney

Mutations in approximately 80 genes have been implicated as the cause of various genetic kidney diseases. However, gene delivery to kidney cells from the blood is inefficient because of the natural filtering functions of the glomerulus, and research into and development of gene therapy directed toward kidney disease has lagged behind as compared with hepatic, neuromuscular, and ocular gene therapy. This lack of progress is in spite of numerous genetic mouse models of human disease available to the research community and many vectors in existence that can theoretically deliver genes to kidney cells with high efficiency. In the past decade, several groups have begun to develop novel injection techniques in mice, such as retrograde ureter, renal vein, and direct subcapsular injections to help resolve the issue of gene delivery to the kidney through the blood. In addition, the ability to retarget vectors specifically toward kidney cells has been underutilized but shows promise. This review discusses how recent advances in gene delivery to the kidney and the field of gene therapy can leverage the wealth of knowledge of kidney genetics to work toward developing gene therapy products for patients with kidney disease.

Tunneling Nanotubes and the Eye: Intercellular Communication and Implications for Ocular Health and Disease

Cellular communication is an essential process for the development and maintenance of all tissues including the eye. Recently, a new method of cellular communication has been described, which relies on formation of tubules, called tunneling nanotubes (TNTs). These structures connect the cytoplasm of adjacent cells and allow the direct transport of cellular cargo between cells without the need for secretion into the extracellular milieu. TNTs may be an important mechanism for signaling between cells that reside long distances from each other or for cells in aqueous environments, where diffusion-based signaling is challenging. Given the wide range of cargoes transported, such as lysosomes, endosomes, mitochondria, viruses, and miRNAs, TNTs may play a role in normal homeostatic processes in the eye as well as function in ocular disease. This review will describe TNT cellular communication in ocular cell cultures and the mammalian eye in vivo, the role of TNTs in mitochondrial transport with an emphasis on mitochondrial eye diseases, and molecules involved in TNT biogenesis and their function in eyes, and finally, we will describe TNT formation in inflammation, cancer, and stem cells, focusing on pathological processes of particular interest to vision scientists.

Mitochondrial characteristics contribute to proliferation and migration potency of MDA-MB-231 cancer cells and their response to cisplatin treatment

AIM

Despite recent advances in therapeutic strategies, cancer is still a leading cause of mortality worldwide. Mitochondrial dysfunction is implicated in cancer initiation and metastasis, and even in chemo- and radio-resistance. However, the precise role of mitochondria in cancer is crosstalk and controversial. This study is trying to find out the effect of transferring normal mitochondria into the highly aggressive and proliferative MDA-MB-231 cancer cells, and to evaluate the effect of the transfer with/without a combination therapy with cisplatin.

MATERIALS AND METHODS

Normal mitochondria were isolated from human umbilical cord derived-mesenchymal stem cells. The mitochondria were transferred into the MDA-MB-231 cells, and also into cells with mitochondrial dysfunction induced by rhodamine red 6 (R6G). Cell proliferation and sensitivity of the cells to cisplatin were measured by cell counting after the mitochondria transfer. Also, apoptosis was evaluated by DAPI staining and in situ cell death detection (TdT-mediated dUTP nickend labeling; TUNEL) methods. Migration capability of the cells was studied by transwell assay.

KEY FINDINGS

Transfer of normal mitochondria into MDA-MB-231 cells increased cell proliferation. However, the transfer of mitochondria enhanced cisplatin-induced apoptosis in MDA-MB-231 cells in which mitochondria were already disrupted. Introduction of normal cell-derived mitochondria into the MDA-MB-231 cells increased their invasive, but decreased the migration potency of the cells in the group with mitochondrial dysfunction (MDA + RG6 + Cisplatin).

CONCLUSION

The introduction of healthy mitochondria to highly aggressive and proliferative cells would be considered as a new therapeutic modality for some types of cancer.

Mesenchymal stem cells elicit macrophages into M2 phenotype via improving transcription factor EB-mediated autophagy to alleviate diabetic nephropathy

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease. Chronic inflammation is recognized as a key causal factor in the development and progression of DN, and the imbalance of M1/M2 macrophages (Mφ) contributes to this process. Mesenchymal stem cells (MSCs) have been reported to prevent renal injuries via immune regulation in diabetic models, but whether these benefits are owing to the regulation of Mφ, and the underlying signaling pathways are unknown. Here, we showed that MSCs elicited Mφ into M2 phenotype and prevented renal injuries in DN mice, but these effects were abolished when the Mφ were depleted by clodronate liposomes (Lipo-Clod), suggesting that Mφ were necessary for renal protection of MSCs in DN mice. Moreover, the MSCs promoted M2 polarization was attributable to the activation of transcription factor EB (TFEB) and subsequent restore of lysosomal function and autophagy activity in Mφ. Furthermore, in vivo adoptive transfer of Mφ^{in vivo} (Mφ from DN + MSCs mice) or Mφ^MSCs (Mφ cocultured with MSCs in vitro) to DN mice improved renal function. While, TFEB knockdown in Mφ significantly abolished the protective role of Mφ^MSCs . Altogether, these findings revealed that MSCs suppress inflammatory response and alleviate renal injuries in DN mice via TFEB-dependent Mφ switch.

Macrophage polarization impacts tunneling nanotube formation and intercellular organelle trafficking

Tunneling nanotubes (TNTs) are cellular extensions enabling cytosol-to-cytosol intercellular interaction between numerous cell types including macrophages. Previous studies of hematopoietic stem and progenitor cell (HSPC) transplantation for the lysosomal storage disorder cystinosis have shown that HSPC-derived macrophages form TNTs to deliver cystinosin-bearing lysosomes to cystinotic cells, leading to tissue preservation. Here, we explored if macrophage polarization to either proinflammatory M1-like M(LPS/IFNγ) or anti-inflammatory M2-like M(IL-4/IL-10) affected TNT-like protrusion formation, intercellular transport and, ultimately, the efficacy of cystinosis prevention. We designed new automated image processing algorithms used to demonstrate that LPS/IFNγ polarization decreased bone marrow-derived macrophages (BMDMs) formation of protrusions, some of which displayed characteristics of TNTs, including cytoskeletal structure, 3D morphology and size. In contrast, co-culture of macrophages with cystinotic fibroblasts yielded more frequent and larger protrusions, as well as increased lysosomal and mitochondrial intercellular trafficking to the diseased fibroblasts. Unexpectedly, we observed normal protrusion formation and therapeutic efficacy following disruption of anti-inflammatory IL-4/IL-10 polarization in vivo by transplantation of HSPCs isolated from the Rac2-/- mouse model. Altogether, we developed unbiased image quantification systems that probe mechanistic aspects of TNT formation and function in vitro, while HSPC transplantation into cystinotic mice provides a complex in vivo disease model. While the differences between polarization cell culture and mouse models exemplify the oversimplicity of in vitro cytokine treatment, they simultaneously demonstrate the utility of our co-culture model which recapitulates the in vivo phenomenon of diseased cystinotic cells stimulating thicker TNT formation and intercellular trafficking from macrophages. Ultimately, we can use both approaches to expand the utility of TNT-like protrusions as a delivery system for regenerative medicine.

Potential use of stem cells as a therapy for cystinosis

Cystinosis is an autosomal recessive metabolic disease that belongs to the family of lysosomal storage disorders (LSDs). Initial symptoms of cystinosis correspond to the renal Fanconi syndrome. Patients then develop chronic kidney disease and multi-organ failure due to accumulation of cystine in all tissue compartments. LSDs are commonly characterized by a defective activity of lysosomal enzymes. Hematopoietic stem and progenitor cell (HSPC) transplantation is a treatment option for several LSDs based on the premise that their progeny will integrate in the affected tissues and secrete the functional enzyme, which will be recaptured by the surrounding deficient cells and restore physiological activity. However, in the case of cystinosis, the defective protein is a transmembrane lysosomal protein, cystinosin. Thus, cystinosin cannot be secreted, and yet, we showed that HSPC transplantation can rescue disease phenotype in the mouse model of cystinosis. In this review, we are describing a different mechanism by which HSPC-derived cells provide cystinosin to diseased cells within tissues, and how HSPC transplantation could be an effective one-time treatment to treat cystinosis but also other LSDs associated with a lysosomal transmembrane protein dysfunction.

Tuberculosis Exacerbates HIV-1 Infection through IL-10/STAT3-Dependent Tunneling Nanotube Formation in Macrophages

The tuberculosis (TB) bacillus, Mycobacterium tuberculosis (Mtb), and HIV-1 act synergistically; however, the mechanisms by which Mtb exacerbates HIV-1 pathogenesis are not well known. Using in vitro and ex vivo cell culture systems, we show that human M(IL-10) anti-inflammatory macrophages, present in TB-associated microenvironment, produce high levels of HIV-1. In vivo, M(IL-10) macrophages are expanded in lungs of co-infected non-human primates, which correlates with disease severity. Furthermore, HIV-1/Mtb co-infected patients display an accumulation of M(IL-10) macrophage markers (soluble CD163 and MerTK). These M(IL-10) macrophages form direct cell-to-cell bridges, which we identified as tunneling nanotubes (TNTs) involved in viral transfer. TNT formation requires the IL-10/STAT3 signaling pathway, and targeted inhibition of TNTs substantially reduces the enhancement of HIV-1 cell-to-cell transfer and overproduction in M(IL-10) macrophages. Our study reveals that TNTs facilitate viral transfer and amplification, thereby promoting TNT formation as a mechanism to be explored in TB/AIDS potential therapeutics.

Expansion of Islet-Resident Macrophages Leads to Inflammation Affecting β Cell Proliferation and Function in Obesity

The nature of obesity-associated islet inflammation and its impact on β cell abnormalities remains poorly defined. Here, we explore immune cell components of islet inflammation and define their roles in regulating β cell function and proliferation. Islet inflammation in obese mice is dominated by macrophages. We identify two islet-resident macrophage populations, characterized by their anatomical distributions, distinct phenotypes, and functional properties. Obesity induces the local expansion of resident intra-islet macrophages, independent of recruitment from circulating monocytes. Functionally, intra-islet macrophages impair β cell function in a cell-cell contact-dependent manner. Increased engulfment of β cell insulin secretory granules by intra-islet macrophages in obese mice may contribute to restricting insulin secretion. In contrast, both intra- and peri-islet macrophage populations from obese mice promote β cell proliferation in a PDGFR signaling-dependent manner. Together, these data define distinct roles and mechanisms for islet macrophages in the regulation of islet β cells.

Concise Review: Intercellular Communication Via Organelle Transfer in the Biology and Therapeutic Applications of Stem Cells

The therapeutic potential of stem cell-based therapies may be largely dependent on the ability of stem cells to modulate host cells rather than on their differentiation into host tissues. Within the last decade, there has been considerable interest in the intercellular communication mediated by the transfer of cytoplasmic material and organelles between cells. Numerous studies have shown that mitochondria and lysosomes are transported between cells by various mechanisms, such as tunneling nanotubes, microvesicles, and cellular fusion. This review will focus on the known instances of organelle transfer between stem cells and differentiated cells, what effects it has on recipient cells and how organelle transfer is regulated. Stem Cells 2019;37:14-25.