A cAMP signalosome in primary cilia drives gene expression and kidney cyst formation.

The primary cilium constitutes an organelle that orchestrates signal transduction independently from the cell body. Dysregulation of this intricate molecular architecture leads to severe human diseases, commonly referred to as ciliopathies. However, the molecular underpinnings how ciliary signaling orchestrates a specific cellular output remain elusive. By combining spatially resolved optogenetics with RNA sequencing and imaging, we reveal a novel cAMP signalosome that is functionally distinct from the cytoplasm. We identify the genes and pathways targeted by the ciliary cAMP signalosome and shed light on the underlying mechanisms and downstream signaling. We reveal that chronic stimulation of the ciliary cAMP signalosome transforms kidney epithelia from tubules into cysts. Counteracting this chronic cAMP elevation in the cilium by small molecules targeting activation of phosphodiesterase-4 long isoforms inhibits cyst growth. Thereby, we identify a novel concept of how the primary cilium controls cellular functions and maintains tissue integrity in a specific and spatially distinct manner and reveal novel molecular components that might be involved in the development of one of the most common genetic diseases, polycystic kidney disease.

Development of oxaalkyne and alkyne fatty acids as novel tracers to study fatty acid beta-oxidation pathways and intermediates.

Fatty acid beta-oxidation is a key process in mammalian lipid catabolism. Disturbance of this process results in severe clinical symptoms, including dysfunction of the liver, a major beta-oxidizing tissue. For a thorough understanding of this process, a comprehensive analysis of involved fatty acid and acyl-carnitine intermediates is desired, but capable methods are lacking. Here, we introduce oxaalkyne and alkyne fatty acids as novel tracers to study the beta-oxidation of long- and medium-chain fatty acids in liver lysates and primary hepatocytes. Combining these new tracer tools with highly sensitive chromatography and mass spectrometry analyses, this study confirms differences in metabolic handling of fatty acids of different chain length. Unlike longer chains, we found that medium-chain fatty acids that were activated inside or outside of mitochondria by different acyl-CoA synthetases could enter mitochondria in the form of free fatty acids or as carnitine esters. Upon mitochondrial beta-oxidation, shortened acyl-carnitine metabolites were then produced and released from mitochondria. In addition, we show that hepatocytes ultimately also secreted these shortened acyl chains into their surroundings. Furthermore, when mitochondrial beta-oxidation was hindered, we show that peroxisomal beta-oxidation likely acts as a salvage pathway, thereby maintaining the levels of shortened fatty acid secretion. Taken together, we conclude that this new method based on oxaalkyne and alkyne fatty acids allows for metabolic tracing of the beta-oxidation pathway in tissue lysate and in living cells with unique coverage of metabolic intermediates and at unprecedented detail.

Multiplexed and single cell tracing of lipid metabolism.

Cellular lipid metabolism is a complex network process comprising dozens of enzymes, multiple organelles and more than a thousand lipid species. Tracing metabolic reactions in this network is a major technological and scientific challenge. Using a click-chemistry mass spectrometry reporter strategy, we have developed a specific, highly sensitive and robust tracing procedure for alkyne-labeled lipids. The method enables sample multiplexing, which improves sample comparison. We demonstrate this by a time-resolved analysis of hepatocyte glycerolipid metabolism with parallel quantitative monitoring of 120 labeled lipid species. The subfemtomole sensitivity enabled a single cell analysis of fatty acid incorporation into neutral and membrane lipids. The results demonstrate the robustness of lipid homeostasis at the single cell level.

Association of Disease-Modifying Treatment With Outcome in Patients With Relapsing Multiple Sclerosis and Isolated MRI Activity.

BACKGROUND AND OBJECTIVES: Isolated value of MRI metrics in relapsing multiple sclerosis (RMS) as a surrogate marker of response to disease-modifying treatment (DMT) and, thus, as decision criteria for DMT escalation in the absence of clinical signs of disease activity is still a matter of debate. The aim of this study was to investigate whether DMT escalation based on isolated MRI activity affects clinical outcome. METHODS: Combining data from 5 MS centers in Austria and Switzerland, we included patients with RMS aged at least 18 years who (1) had initiated first-line, low-to-moderate-efficacy DMT (interferon ß, glatiramer acetate, teriflunomide, or dimethyl fumarate) continued for ≥12 months, (2) were clinically stable (no relapses or disability progression) on DMT for 12 months, (3) had MRI at baseline and after 12 months on DMT, and (4) had available clinical follow-up for ≥2 years after the second MRI. The primary endpoint was occurrence of relapse during follow-up. The number of new T2 lesions (T2L) and DMT strategy (continuing low-/moderate-efficacy DMT vs escalating DMT) were used as covariates in regression analyses. RESULTS: A total of 131 patients with RMS, median age of 36 (25th-75th percentiles: 29-43) years, 73% women, were included and observed over a median period of 6 (5-9) years after second MRI. Sixty-two (47%) patients had relapse. Patients who continued first-line DMT had a 3-fold increased risk of relapse given 2 new T2L (hazard ratio [HR] 3.2, lower limit [LL] of 95% CI: 1.5) and a 4-fold increased risk given ≥3 new T2L (HR 4.0, LL-CI: 2.1). Escalation of DMT lowered the risk of relapse in patients with 2 new T2L by approximately 80% (HR 0.2, upper limit [UL] of 95% CI: 1.3) and with ≥3 new T2L by 70% (HR 0.3, UL-CI: 0.8). In case of only 1 new T2L, the increased risk of relapse and the treatment effect did not reach statistical significance of 5%. DISCUSSION: In our real-world cohort of patients clinically stable under low-to-moderate-efficacy DMT, escalation of DMT based on isolated MRI activity decreased risk of further relapse when at least 2 new T2L had occurred. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that clinically stable patients with MS on low-/moderate-efficacy DMT with ≥3 new T2L on MRI who escalate DMT have a reduced risk of relapse and Expanded Disability Status Scale progression.

Cold-induced expression of a truncated adenylyl cyclase 3 acts as rheostat to brown fat function.

Promoting brown adipose tissue (BAT) activity innovatively targets obesity and metabolic disease. While thermogenic activation of BAT is well understood, the rheostatic regulation of BAT to avoid excessive energy dissipation remains ill-defined. Here, we demonstrate that adenylyl cyclase 3 (AC3) is key for BAT function. We identified a cold-inducible promoter that generates a 5' truncated AC3 mRNA isoform (Adcy3-at), whose expression is driven by a cold-induced, truncated isoform of PPARGC1A (PPARGC1A-AT). Male mice lacking Adcy3-at display increased energy expenditure and are resistant to obesity and ensuing metabolic imbalances. Mouse and human AC3-AT are retained in the endoplasmic reticulum, unable to translocate to the plasma membrane and lack enzymatic activity. AC3-AT interacts with AC3 and sequesters it in the endoplasmic reticulum, reducing the pool of adenylyl cyclases available for G-protein-mediated cAMP synthesis. Thus, AC3-AT acts as a cold-induced rheostat in BAT, limiting adverse consequences of cAMP activity during chronic BAT activation.

AdipoQ-a simple, open-source software to quantify adipocyte morphology and function in tissues and in vitro.

The different adipose tissues (ATs) can be distinguished according to their function. For example, white AT stores energy in form of lipids, whereas brown AT dissipates energy in the form of heat. These functional differences are represented in the respective adipocyte morphology; whereas white adipocytes contain large, unilocular lipid droplets, brown adipocytes contain smaller, multilocular lipid droplets. However, an automated, image analysis pipeline to comprehensively analyze adipocytes in vitro in cell culture as well as ex vivo in tissue sections is missing. We here present AdipoQ, an open-source software implemented as ImageJ plugins that allows us to analyze adipocytes in tissue sections and in vitro after histological and/or immunofluorescent labeling. AdipoQ is compatible with different imaging modalities and staining methods, allows batch processing of large datasets and simple post-hoc analysis, provides a broad band of parameters, and allows combining multiple fluorescent readouts. Therefore AdipoQ is of immediate use not only for basic research but also for clinical diagnosis.

Cell-Autonomous Control of Neuronal Dendrite Expansion via the Fatty Acid Synthesis Regulator SREBP.

During differentiation, neurons require a high lipid supply for membrane formation as they elaborate complex dendritic morphologies. While glia-derived lipids support neuronal growth during development, the importance of cell-autonomous lipid production for dendrite formation has been unclear. Using Drosophila larva dendritic arborization (da) neurons, we show that dendrite expansion relies on cell-autonomous fatty acid production. The nociceptive class four (CIV) da neurons form particularly large space-filling dendrites. We show that dendrite formation in these CIVda neurons additionally requires functional sterol regulatory element binding protein (SREBP), a crucial regulator of fatty acid production. The dendrite simplification in srebp mutant CIVda neurons is accompanied by hypersensitivity of srebp mutant larvae to noxious stimuli. Taken together, our work reveals that cell-autonomous fatty acid production is required for proper dendritic development and establishes the role of SREBP in complex neurons for dendrite elaboration and function.