Mitochondrial diversity probed in mouse cerebellum elucidates cell type-specific fine-tuning of mitochondrial biology

Mitochondria house a variety of cellular functions, including catabolic and anabolic pathways, apoptosis and Ca2+ handling. These functions critically depend on nuclear-encoded proteins given that mitochondrial DNA only encodes for 13 proteins, which are incorporated into the respiratory chain. While mitochondria differ in morphology and functions among tissues in vivo, mitochondrial diversity among cell types is less well understood – especially in heterogeneous tissues such as the nervous system. Here, I present an in vivo tool for the characterization of cell type-specific mitochondria in mouse. Via the MitoTag mouse model, mitochondria from the cell type of interest are tagged in a Cre recombinase-dependent manner with GFP, which is localized to the outer mitochondrial membrane (GFP-OMM). This tagging allows for the immunocapture of organelles and their subsequent investigation through functional assays and omics-based screenings. We applied the MitoTag approach to the cerebellum and profiled the mitochondrial proteome of Purkinje cells, granule cells and astrocytes. Among these cell types, we found 196 proteins differentially enriched, of which 19 candidates were independently confirmed as cell type-enriched mitochondrial ‘markers’. Further analysis revealed functional specializations that we corroborated in independent assays using immunocaptured mitochondria. Specifically, astrocytic mitochondria superiorly oxidized long-chain fatty acids, while neuronal mitochondria demonstrated enhanced Ca2+ uptake via the mitochondrial calcium uniporter in granule cells and enhanced contact sites with the endoplasmic reticulum via regulator of microtubule dynamics protein 3 in Purkinje cells. In studies across species, I confirmed that neural mitochondrial diversity is conserved in the nervous system of mammals, aves and amphibian. Hence, we used neuronal and astrocytic mitochondrial ‘markers’ to show mitochondrial pathology in mouse models and human cases of Alzheimer’s disease and amyotrophic lateral sclerosis. The MitoTag approach enables mitochondrial research in a defined cellular context in vivo. Future applications will reveal the cell type-specific fine-tuning of mitochondria in many contexts, such as development, aging and diseases, as well as their contribution to the selective vulnerability of certain cell types

Targeting the TCA cycle can ameliorate widespread axonal energy deficiency in neuroinflammatory lesions

Inflammation in the central nervous system can impair the function of neuronal mitochondria and contributes to axon degeneration in the common neuroinflammatory disease multiple sclerosis (MS). Here we combine cell-type-specific mitochondrial proteomics with in vivo biosensor imaging to dissect how inflammation alters the molecular composition and functional capacity of neuronal mitochondria. We show that neuroinflammatory lesions in the mouse spinal cord cause widespread and persisting axonal ATP deficiency, which precedes mitochondrial oxidation and calcium overload. This axonal energy deficiency is associated with impaired electron transport chain function, but also an upstream imbalance of tricarboxylic acid (TCA) cycle enzymes, with several, including key rate-limiting, enzymes being depleted in neuronal mitochondria in experimental models and in MS lesions. Notably, viral overexpression of individual TCA enzymes can ameliorate the axonal energy deficits in neuroinflammatory lesions, suggesting that TCA cycle dysfunction in MS may be amendable to therapy

Chronic exposure to insecticides impairs honeybee optomotor behaviour

Honeybees use wide-field visual motion information to calculate the distance they have flown from the hive, and this information is communicated to conspecifics during the waggle dance. Seed treatment insecticides, including neonicotinoids and novel insecticides like sulfoxaflor, display detrimental effects on wild and managed bees, even when present at sublethal quantities. These effects include deficits in flight navigation and homing ability, and decreased survival of exposed worker bees. Neonicotinoid insecticides disrupt visual motion detection in the locust, resulting in impaired escape behaviors, but it had not previously been shown whether seed treatment insecticides disrupt wide-field motion detection in the honeybee. Here, we show that sublethal exposure to two commonly used insecticides, imidacloprid (a neonicotinoid) and sulfoxaflor, results in impaired optomotor behavior in the honeybee. This behavioral effect correlates with altered stress and detoxification gene expression in the brain. Exposure to sulfoxaflor led to sparse increases in neuronal apoptosis, localized primarily in the optic lobes, however there was no effect of imidacloprid. We propose that exposure to cholinergic insecticides disrupts the honeybee’s ability to accurately encode wide-field visual motion, resulting in impaired optomotor behaviors. These findings provide a novel explanation for previously described effects of neonicotinoid insecticides on navigation and link these effects to sulfoxaflor for which there is a gap in scientific knowledge

CCL17-expressing dendritic cells drive atherosclerosis by restraining regulatory T cell homeostasis in mice

Immune mechanisms are known to control the pathogenesis of atherosclerosis. However, the exact role of DCs, which are essential for priming of immune responses, remains elusive. We have shown here that the DC-derived chemokine CCL17 is present in advanced human and mouse atherosclerosis and that CCL17+ DCs accumulate in atherosclerotic lesions. In atherosclerosis-prone mice, Ccl17 deficiency entailed a reduction of atherosclerosis, which was dependent on Tregs. Expression of CCL17 by DCs limited the expansion of Tregs by restricting their maintenance and precipitated atherosclerosis in a mechanism conferred by T cells. Conversely, a blocking antibody specific for CCL17 expanded Tregs and reduced atheroprogression. Our data identify DC-derived CCL17 as a central regulator of Treg homeostasis, implicate DCs and their effector functions in atherogenesis, and suggest that CCL17 might be a target for vascular therapy

Neoadjuvant systemic therapy in melanoma: recommendations of the International Neoadjuvant Melanoma Consortium

Advances in the treatment of metastatic melanoma have improved responses and survival. However, many patients continue to experience resistance or toxicity to treatment, highlighting a crucial need to identify biomarkers and understand mechanisms of response and toxicity. Neoadjuvant therapy for regional metastases might improve operability and clinical outcomes over upfront surgery and adjuvant therapy, and has become an established role for drug development and biomarker discovery in other cancers (including locally advanced breast cancer, head and neck squamous cell carcinomas, gastroesophageal cancer, and anal cancer). Patients with clinically detectable stage III melanoma are ideal candidates for neoadjuvant therapy, because they represent a high-risk patient population with poor outcomes when treated with upfront surgery alone. Neoadjuvant therapy is now an active area of research for melanoma with numerous completed and ongoing trials (since 2014) with disparate designs, endpoints, and analyses under investigation. We have, therefore, established the International Neoadjuvant Melanoma Consortium with experts in medical oncology, surgical oncology, pathology, radiation oncology, radiology, and translational research to develop recommendations for investigating neoadjuvant therapy in melanoma to align future trial designs and correlative analyses. Alignment and consistency of neoadjuvant trials will facilitate optimal data organisation for future regulatory review and strengthen translational research across the melanoma disease continuum