Mónica Vara-Pérez

Emerging evidence suggests that Parkinson’s disease (PD) may have its origin in the enteric nervous system (ENS), from where α-synuclein (αS) pathology spreads to the brain^1,2,3,4. Decades before the onset of motor symptoms, patients with PD suffer from constipation and present with circulating T cells responsive to αS, suggesting that peripheral immune responses initiated in the ENS may be involved in the early stages of PD^1,5,6,7. However, cellular mechanisms that trigger αS pathology in the ENS and its spread along the gut–brain axis remain elusive. Here we demonstrate that muscularis macrophages (ME-Macs), housekeepers of ENS integrity and intestinal homeostasis, modulate αS pathology and neurodegeneration in models of PD^8,9. ME-Macs contain misfolded αS, adopt a signature reflecting endolysosomal dysfunction and modulate the expansion of T cells that travel from the ENS to the brain through the dura mater as αS pathology progresses. Directed ME-Mac depletion leads to reduced αS pathology in the ENS and central nervous system, prevents T cell expansion and mitigates neurodegeneration and motor dysfunction, suggesting a role for ME-Macs as early cellular initiators of αS pathology along the gut–brain axis. Understanding these mechanisms could pave the way for early-stage biomarkers in PD.

Brain–immune cross-talk and neuroinflammation critically shape brain physiology in health and disease. A detailed understanding of the brain immune landscape is essential for developing new treatments for neurological disorders. Single-cell technologies offer an unbiased assessment of the heterogeneity, dynamics and functions of immune cells. Here we provide a protocol that outlines all the steps involved in performing single-cell multi-omic analysis of the brain immune compartment. This includes a step-by-step description on how to microdissect the border regions of the mouse brain, together with dissociation protocols tailored to each of these tissues. These combine a high yield with minimal dissociation-induced gene expression changes. Next, we outline the steps involved for high-dimensional flow cytometry and droplet-based single-cell RNA sequencing via the 10x Genomics platform, which can be combined with cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) and offers a higher throughput than plate-based methods. Importantly, we detail how to implement CITE-seq with large antibody panels to obtain unbiased protein-expression screening coupled to transcriptome analysis. Finally, we describe the main steps involved in the analysis and interpretation of the data. This optimized workflow allows for a detailed assessment of immune cell heterogeneity and activation in the whole brain or specific border regions, at RNA and protein level. The wet lab workflow can be completed by properly trained researchers (with basic proficiency in cell and molecular biology) and takes between 6 and 11 h, depending on the chosen procedures. The computational analysis requires a background in bioinformatics and programming in R.

Melanoma cells exploit mitophagy and hypoxia signaling to promote their growth. In a recent study, we found that loss of B-cell lymphoma 2 (BCL-2)/adenovirus E1B 19kDa protein-interacting protein 3 (BNIP3) curbed Hypoxia Inducible Factor 1 alpha (HIF-1α) levels and melanoma growth in vivo. Insufficient levels of BNIP3 boost iron-driven prolyl hydroxylase 2 (Phd2)-mediated degradation of HIF-1α by exacerbating nuclear receptor activator 4 (Ncoa4)-mediated ferritinophagy. Thus, BNIP3 promotes melanoma growth by controlling iron metabolism.

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In the past years, we have learnt that tumors co-evolve with their microenvironment, and that the active interaction between cancer cells and stromal cells plays a pivotal role in cancer initiation, progression and treatment response. Among the players involved, the pathways regulating mitochondrial functions have been shown to be crucial for both cancer and stromal cells. This is perhaps not surprising, considering that mitochondria in both cancerous and non-cancerous cells are decisive for vital metabolic and bioenergetic functions and to elicit cell death. The central part played by mitochondria also implies the existence of stringent mitochondrial quality control mechanisms, where a specialized autophagy pathway (mitophagy) ensures the selective removal of damaged or dysfunctional mitochondria. Although the molecular underpinnings of mitophagy regulation in mammalian cells remain incomplete, it is becoming clear that mitophagy pathways are intricately linked to the metabolic rewiring of cancer cells to support the high bioenergetic demand of the tumor. In this review, after a brief introduction of the main mitophagy regulators operating in mammalian cells, we discuss emerging cell autonomous roles of mitochondria quality control in cancer onset and progression. We also discuss the relevance of mitophagy in the cellular crosstalk with the tumor microenvironment and in anti-cancer therapy responses.

Whereas significant anti-tumor responses are observed in most BRAF^V600E-mutant melanoma patients exposed to MAPK-targeting agents, resistance almost invariably develops. Here, we show that in therapy-responsive cells BRAF inhibition induces downregulation of the processing of Sterol Regulator Element Binding (SREBP-1) and thereby lipogenesis. Irrespective of the escape mechanism, therapy-resistant cells invariably restore this process to promote lipid saturation and protect melanoma from ROS-induced damage and lipid peroxidation. Importantly, pharmacological SREBP-1 inhibition sensitizes BRAF^V600E-mutant therapy-resistant melanoma to BRAF^V600E inhibitors both in vitro and in a pre-clinical PDX in vivo model. Together, these data indicate that targeting SREBP-1-induced lipogenesis may offer a new avenue to overcome acquisition of resistance to BRAF-targeted therapy. This work also provides evidence that targeting vulnerabilities downstream of oncogenic signaling offers new possibilities in overcoming resistance to targeted therapies.

Aerobic glycolysis (‘Warburg effect’) is used by cancer cells to fuel tumor growth. Interestingly, metastatic melanoma cells rely on glutaminolysis rather than aerobic glycolysis for their bioenergetic needs through the tricarboxylic acid (TCA) cycle. Here, we compared the effects of glucose or glutamine on melanoma cell proliferation, migration and oxidative phosphorylation in vitro. We found that glutamine-driven melanoma cell’s aggressive traits positively correlated with increased expression of HIF1α and its pro-autophagic target BNIP3. BNIP3 silencing reduced glutamine-mediated effects on melanoma cell growth, migration and bioenergetics. Hence, BNIP3 is a vital component of the mitochondria quality control required for glutamine-driven melanoma aggressiveness.

Dendritic cell (DC)-based vaccines against cancer have been extensively developed over the past two decades. Typically DC-based cancer immunotherapy entails loading patient-derived DCs with an appropriate source of tumor-associated antigens (TAAs) and efficient DC stimulation through a so-called "maturation cocktail" (typically a combination of pro-inflammatory cytokines and Toll-like receptor agonists), followed by DC reintroduction into patients. DC vaccines have been documented to (re)activate tumor-specific T cells in both preclinical and clinical settings. There is considerable clinical interest in combining DC-based anticancer vaccines with T cell-targeting immunotherapies. This reflects the established capacity of DC-based vaccines to generate a pool of TAA-specific effector T cells and facilitate their infiltration into the tumor bed. In this Trial Watch, we survey the latest trends in the preclinical and clinical development of DC-based anticancer therapeutics. We also highlight how the emergence of immune checkpoint blockers and adoptive T-cell transfer-based approaches has modified the clinical niche for DC-based vaccines within the wide cancer immunotherapy landscape.