Biology subjects

Wyss, M. T.

Publications and source records attributed to Wyss, M. T..

9 recordsLinked to original sources

bioRxiv2026

A longitudinal two-photon imaging platform for focal astrocyte ablation in vivo

Investigating the consequences of astrocyte loss in the intact brain is both important and challenging. As integral components of the neuro-glia-vascular unit, astrocytes are involved in a variety of brain processes including water homeostasis, metabolic supply, regulation of cerebral blood flow, and coordination of neuronal circuit activity. Astrocyte impairment has been associated with numerous neurological disorders. However, experimental models combining focal astrocyte ablation with longitudinal in vivo imaging in the intact adult brain have been lacking, limiting efforts to define the causal contribution of astrocyte loss to central nervous system (CNS) pathology and repair. Here, we present an in vivo model of antibody-mediated astrocyte ablation that enables longitudinal imaging and detailed investigation of ensuing cellular responses. It integrates focal induction of aquaporin-4 antibody-mediated astrocyte loss, chronic in vivo two-photon imaging, genetically encoded sensors, and reporter mouse lines. This advancement allows visualization and quantification of cellular and subcellular events in living organisms during lesion progression and recovery. It overcomes many longstanding limitations of previous models that are either constrained by non-specific hypoxic or mechanical tissue damage or require sacrificing animals at discrete time points, hindering the ability to monitor dynamic biological processes over time. In contrast, the selective targeting of astrocytes prevents the formation of the glial border, enabling the investigation of CNS response in a scar-free environment. Overall, this new approach represents a significant technical advancement, enabling comprehensive longitudinal studies of CNS responses to astrocyte loss, thus opening new avenues for understanding astrocytopathy-driven pathology, evaluating therapeutic interventions, and promoting translational research.

neuroscience↗

bioRxiv2026

Developmental Trajectory of Synaptic Remodeling in the Mouse Prefrontal Cortex

The prefrontal cortex (PFC) is a heteromodal association area critical for higher-order cognitive functions. Its protracted maturation extends through adolescence into early adulthood, a period characterized by extensive remodeling of neuronal networks and synaptic architecture. This heightened plasticity supports the refinement of prefrontal circuits necessary to meet the evolving cognitive and behavioral demands of this developmental transition. However, the extended maturation window also increases vulnerability to environmental perturbations, which can lead to lasting synaptic and cognitive impairments. Despite widespread use of developmental disruption models during adolescence, a systematic characterization of synaptic dynamics during normal PFC maturation is lacking. Here, we combined longitudinal in vivo two-photon imaging of dendritic spines with cross-sectional quantification of excitatory and inhibitory synapses, and microglia-mediated synaptic engulfment, in mice from juvenile to adult stages. This integrated approach provides a comprehensive reference atlas of normal prefrontal synaptic maturation, offering a framework for interpreting alterations to synapses in models of developmental disturbance.

neuroscience↗

bioRxiv2025

Pial collaterals propagate neurovascular responses across functional units

Neurovascular coupling refers to the regulation of cerebral blood flow in response to neuronal activity, a process forming the basis for multiple functional neuroimaging techniques. However, the mechanisms that coordinate neurovascular responses across distinct cortical arterial territories remain poorly understood. Here we show that pial collaterals, arterio-arterial connections traditionally considered dormant under physiological conditions, serve as active conduits that propagate neurovascular signals between adjacent cortical territories and functional units. We demonstrate that neuronal activity in the somatosensory cortex triggers direct vascular signaling via endothelial Kir2.1 channels through pial collaterals, synchronizing blood flow responses beyond the activated area. The loss of pial collaterals abolished inter-territorial coupling without affecting local neurovascular responses. These results reveal that pial collaterals are critical regulators of cerebral perfusion.

neuroscience↗

bioRxiv2025

ECgo: All-Optical Induction of Single Endothelial Cell Injury and Capillary Occlusion in the Brain

The ability to induce endothelial cell (EC) damage in the mouse brain with high spatial precision is invaluable for mechanistic studies of brain capillary injury and repair. Here, we introduce an optical method, termed ECgo, that utilizes a new two-photon-excitable porphyrin-based photosensitizer (Ps2P) to selectively obliterate single ECs within the brain microvascular network. Using the developed approach, we were able to induce occlusions of single capillaries with high spatiotemporal control, while preserving the surrounding tissue. Combined with longitudinal two-photon imaging, ECgo enables studies of morphological and functional consequences of targeted single capillary EC injury in vivo under healthy and diseased conditions. SIGNIFICANCE STATEMENTBrain capillary injury is a common feature of aging and many neurological disorders. While a single capillary lesion may appear inconsequential, the cumulative effect of repeated and spatially dispersed capillary insults can lead to substantial brain dysfunction. Understanding how single capillary injuries contribute cumulatively to long-term brain damage requires tools that can precisely target individual capillaries in the living brain. Here, we introduce an optical method that uses a new light-activatable compound to selectively injure single brain capillaries with high spatial accuracy. Our method enables detailed, longitudinal studies of capillary repair, blood flow recovery, local oxygen dynamics, and glial responses following microvascular injury.

neuroscience↗

bioRxiv2024

A low-cost FPGA-based approach for pile-up corrected high-speed in vivo FLIM imaging

Intensity-based two-photon microscopy (2PM) is a cornerstone of biomedical research but lacks the ability to measure concentrations, a pivotal task for longitudinal studies and quantitative comparisons. Fluorescence Lifetime Imaging (FLIM) based on Time-Correlated Single Photon Counting (TCSPC) can overcome those limits but suffers from "pile-up" distortions at high photon count rates, severely limiting acquisition speed. We introduce the "laser period blind time" (LPBT) method to correct pile-up distortions in photon counting electronics, enabling reliable low-cost TCSPC-FLIM at high count rates. The correction was implemented on low-cost hardware based on a field programable gate array (FPGA) and validated using a combination of in silico simulations and in vitro, ex vivo and in vivo measurements. The LBPT approach achieves <3% error in lifetime measurements at count rates more than ten times higher than traditional limits, allowing robust FLIM imaging of sub-second metabolite dynamics with subcellular resolution. Our work enables high-precision, cost-effective FLIM imaging at rates comparable to commercial systems and at a fraction of the cost, facilitating the adoption of FLIM across all areas of research needing affordable, quantitative live imaging solutions.

neuroscience↗

bioRxiv2024

Overactivation of prefrontal astrocytes impairs cognition through the metabolic pathway of central kynurenines

Astrocyte dysfunctions have long been implicated in psychiatric and cognitive disorders, yet the precise mechanisms underlying this association remain elusive. Here, we show that chemogenetic activation of prefrontal astrocytes in mice impairs short-term memory and sensorimotor gating and attenuates the activation of parvalbumin (PV) interneurons in the prefrontal cortex. These alterations are accompanied by increases in prefrontal levels of kynurenic acid (KYNA), a key metabolite of the kynurenine (KYN) pathway, known to be produced by astrocytes, which serves as an endogenous antagonist of NMDA receptors. Pharmacological inhibition of kynurenine aminotransferase II, the key enzyme mediating the transamination of KYN to KYNA, reinstates the astrocyte-mediated impairments in short-term memory and sensorimotor gating, and normalizes the deficits in prefrontal PV interneuron activation. Our study identifies a mechanistic link between overactivation of prefrontal astrocytes, increased production of KYNA, and cognitive as well as cellular dysfunctions involved in major psychiatric disorders and beyond.

neuroscience↗

bioRxiv2024

Lactate-carried Mitochondrial Energy Overflow

We addressed the question of mitochondrial lactate metabolism using genetically-encoded sensors. The organelle was found to contain a dynamic lactate pool that leads to dose- and time-dependent protein lactylation. In neurons, mitochondrial lactate reported blood lactate levels with high fidelity. The exchange of lactate across the inner mitochondrial membrane was found to be mediated by a high affinity H+-coupled transport system involving the mitochondrial pyruvate carrier MPC. Assessment of electron transport chain activity and determination of lactate flux showed that mitochondria are tonic lactate producers, a phenomenon driven by energization and stimulated by hypoxia. We conclude that an overflow mechanism caps the redox level of mitochondria, while saving energy in the form of lactate. One Sentence SummaryMitochondrial lactate production

biochemistry↗

bioRxiv2024

Astrocytes adopt a progenitor-like migratory strategy for regeneration in adult brain

Mature astrocytes become activated upon non-specific tissue damage and contribute to glial scar formation. Proliferation and migration of adult reactive astrocytes after injury is considered very limited. However, the regenerative behavior of individual astrocytes following selective astroglial loss, as seen in astrocytopathies, such as neuromyelitis optica spectrum disorder, remains unexplored. Here, we performed longitudinal in vivo imaging of cortical astrocytes after focal astrocyte ablation in mice. We discovered that perilesional astrocytes develop a remarkable plasticity for efficient lesion repopulation. A subset of mature astrocytes transforms into reactive progenitor-like (REPL) astrocytes that not only undergo multiple asymmetric divisions but also remain in a multinucleated interstage. This regenerative response facilitates efficient migration of newly formed daughter cell nuclei towards unoccupied astrocyte territories. Our findings define the cellular principles of astrocyte plasticity upon focal lesion, unravelling the REPL phenotype as a fundamental regenerative strategy of mature astrocytes to restore astrocytic networks in the adult mammalian brain. Promoting this regenerative phenotype bears therapeutic potential for neurological conditions involving glial dysfunction.

neuroscience↗

bioRxiv2023

Leptomeningeal collaterals regulate reperfusion in ischemic stroke

Recanalization is the mainstay of ischemic stroke treatment. However, even with timely clot removal, many stroke patients recover poorly. Leptomeningeal collaterals (LMCs) are pial anastomotic vessels with yet unknown functions. Utilizing a thrombin-based mouse model of stroke and the gold standard fibrinolytic treatment rt-PA, we here show that LMCs play a critical role in preserving vascular function in ischemic territories. We applied laser speckle contrast imaging, ultrafast ultrasound, and two-photon microscopy, to show that after thrombolysis, LMCs allow for gradual reperfusion resulting in small infarcts. On the contrary, in mice with poor LMCs, distal segments of recanalized arteries collapse and deleterious hyperemia causes hemorrhage and mortality. Accordingly, in stroke patients with poor collaterals undergoing thrombectomy, rapid reperfusion resulted in hemorrhagic transformation and unfavorable recovery. Thus, we identify LMCs as key components regulating reperfusion after stroke. Future therapeutic interventions should aim to enhance collateral function, allowing for gradual reperfusion of ischemic tissues after stroke.

neuroscience↗