Biology subjects

Lauritzen, M.

Publications and source records attributed to Lauritzen, M..

11 recordsLinked to original sources

bioRxiv2025

Two-photon microscopy of brain endothelial glycocalyx uncovers spatial heterogeneity, vesicular transport, and lectin-binding kinetics in the living brain

The endothelial glycocalyx is a key regulator of cerebrovascular function and remains one of the most difficult structures to study in vivo. Here we uncover new structural and dynamical features of the brain endothelial glycocalyx using in vivo two-photon microscopy. We identified glycocalyx enrichment at endothelial junctions and arteriolar branch points, visualized its Vesicular transport in real-time, and found evidence for its compositional Variations along the arteriovenous axis. Fluorescence recovery after photobleaching revealed two distinct kinetics of wheat germ agglutinin binding, including a previously undescribed one. Finally, super-localization of the glycocalyx estimated glycocalyx thickness as 775{+/-}17 nm and 622{+/-}34 nm before and after enzymatic shedding, reconciling discrepancies between past optical and electron microscopy estimates. Together these findings establish the first miltiscale framework of glycocalyx distribution and heterogeneity, transport, and molecular interaction kinetics in the living brain.

neuroscience↗

bioRxiv2025

Brain precapillary sphincters modulate myogenic tone in adult and aged mice

Brain precapillary sphincters, which are surrounded by contractile pericytes and are located at the junction of penetrating arterioles and first-order capillaries, can increase their diameter by [~]30% in a few seconds during sensory stimulation, allowing for rapid control of capillary blood flow over a wide dynamic range. We hypothesized that these properties could help precapillary sphincters maintain the capillary blood flow and shield the downstream capillaries during surges in blood pressure. To test this, we visualized microvessels in adult and old anaesthetized mice using in vivo two-photon microscopy. We showed that a blood pressure surge disrupts both microvascular myogenic response and neurovascular coupling in both adult and old mice, with old mice exhibiting a more diminished myogenic response. Similarly, laser ablation of contractile pericytes encircling precapillary sphincters disrupted neurovascular coupling and myogenic response. The resistance provided by precapillary sphincters may be increasingly important in old mice, where we found changes in the topology of microvessels, potentially affecting microvascular blood flow. Old mice displayed more tortuous penetrating arterioles, reduced pial collateral arteriolar density and altered capillary densities: reduced in the arterial end and increased in the venous end. Our results illustrate how blood pressure surges affect brain microvascular function, underscore the protective role of precapillary sphincters during cerebrovascular autoregulation in response to blood pressure surges and compare vascular topology in adult and old mice in vivo.

neuroscience↗

bioRxiv2025

Multi-omic analysis reveals the unique glycan landscape of the blood-brain barrier glycocalyx

The blood-brain barrier (BBB) glycocalyx is the dense layer of glycans and glycoconjugates that coats the luminal surface of the central nervous system (CNS) vasculature. Despite being the first point of contact between the blood and brain, not much is known about the BBB glycocalyx. Here, we performed a multi-omic investigation of the BBB glycocalyx which revealed a unique glycan landscape characterized by enrichment of sialic acid, chondroitin sulfate, and hyaluronan. We found that the BBB glycocalyx was thicker than glycocalyces in the peripheral vasculature and that hyaluronan was the major contributor to its ultrastructure. Using endothelial RNA sequencing, we found potential genetic determinants for these differences, including BBB enrichment of genes involved in sialic acid addition and peripheral enrichment of Tmem2 and Hyal2, the only known cell-surface hyaluronidases. Glycocalyx degradation and increases in vascular permeability are widely associated with inflammation. However, we found that the BBB glycocalyx remains largely unchanged in neuroinflammation during the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis and that its degradation is not sufficient to alter BBB permeability in health. Moreover, we showed that CNS endothelial sialic acid removal delays onset of EAE, indicating that BBB glycocalyx sialic acid may contribute to the progression of neuroinflammation. These findings underscore the unique and robust nature of the BBB glycocalyx and provide targets and tools for future studies into its role in health and neuroinflammation.

molecular biology↗

bioRxiv2024

The neurovascular coupling response of the aged brain is brain-state dependent.

Brain aging lead to reduced cerebral blood flow and cognitive decline, but how normal aging affects neurovascular coupling (NVC) in the awake brain is unclear. Here, we investigated NVC in relation to calcium changes in vascular mural cells (VMCs) in awake adult and aged mice. We show that NVC responses are reduced and prolonged in the aged brain and that this is more pronounced at the capillary level than in arterioles. However, the overall NVC response, measured as the time integral of vasodilation, is the same in two age groups. In adult, but not in aged mice, the NVC response correlated with Ca2+ signaling in VMCs, while the overall Ca2+ kinetics were slower in aged than in adult mice. In particular, the rate of Ca2+ transport, and the Ca2+ sensitivity of VMCs were reduced in aged mice, explaining the reduced and prolonged vasodilation. Spontaneous locomotion was less frequent and reduced in aged mice as compared to young adult mice, and this was reflected in the slow but prolonged NVC and vascular Ca2+ responses. Taken together, our data characterize the NVC in the aged awake brain as slow but prolonged, and underscoring the importance of brain state in understanding age-related mechanisms.

neuroscience↗

bioRxiv2022

Two-photon microscopy in vivo reveals brain vessel type-specific loss of glycocalyx caused by apoM/S1P signaling impairment.

Increases in adsorptive mediated transcytosis (AMT) at the blood-brain barrier (BBB) are linked to many brain disorders. In a healthy brain, AMT is suppressed by sphingosine-1-phosphate (S1P) receptor 1 (S1PR1) signaling. Low levels of S1P lead to a rise in AMT, but the mechanisms are incompletely understood. Here, we explored whether the rises in AMT are caused by the loss of the endothelial glycocalyx (gcx). We used two-photon microscopy in mice with low S1P plasma levels (Apom-/-) and developed a novel photobleaching approach to measure gcx in vivo at distinct classes of cerebral microvessels, i.e., arterioles, capillaries and venules. We show that S1P signaling impairment reduced gcx in arterioles but not in other vessel segments. The location of gcx loss corresponded to the vascular topology of AMT increases. The S1PR1 agonist SEW2871 restores low levels of AMT in Apom-/- mice but did not restore the gcx within the same time window. We propose that while the gcx loss may contribute to AMT increase, restoring gcx is not necessary for AMT to return to normal. These data establish a new imaging method to study gcx in the living mouse brain, demonstrate zonation of gcx in cerebral microvessels, and suggest differences in vascular susceptibility to gcx loss in disease states.

neuroscience↗

bioRxiv2022

Astrocytic Ca2+ signals partake in inhibitory neurovascular coupling in a brain state-dependent manner.

Neurovascular coupling (NVC) modulates cerebral blood flow to match increased metabolic demand during neuronal excitation. Activation of inhibitory interneurons also increase blood flow, but the basis for this inhibitory NVC is unclear. We performed two-photon microscopy in awake mice to examine the correlation between astrocytic Ca2+ and NVC, evoked by activity in either all (VGATIN) or parvalbumin-positive GABAergic interneurons (PVIN). Optogenetic stimulation of VGATIN and PVIN in the somatosensory cortex triggered astrocytic Ca2+ increases that were abolished by anaesthesia. PVIN evoked astrocytic Ca2+ responses with a short latency that preceded NVC, whereas VGATIN evoked Ca2+ increases that were delayed relative to the NVC response. The early onset in PVIN evoked Ca2+ increases dependent on noradrenaline release from locus coeruleus, which also affected inhibitory NVC. Therefore, NVC mechanisms should be studied in awake mice and, though the relationship between interneuron activity and astrocytic Ca2+ is complex, we found a correlation between astrocyte activity and NVC in PVIN.

neuroscience↗

bioRxiv2020

Nitric oxide, KATP channels and endothelin-1 modulate brain pericyte function, vascular tone and neurovascular coupling

Neurotransmitter-mediated signaling correlates strongly to changes in cerebral blood flow (CBF), and functional neuroimaging relies on the robust coupling between activity and CBF, i.e. neurovascular coupling (NVC). We here reveal that key endothelial signaling molecules, nitric oxide (eNO) and endothelin-1 (ET1), modulate pericyte contractility and that pericyte ATP-sensitive potassium (KATP) channels interact with endothelial factors to modulate vascular tone and NVC. We show that NVC requires local synthesis of cGMP, but not NO derived from endothelial cells. The potent endothelial vasoconstrictor ET1 contracted pericytes by IP3 receptor mediated Ca2+ release and blocked NVC. In comparison, pericyte KATP channel openers increased the diameter of capillaries by deactivation of L-type Ca2+ channels while KATP blockers shortened the NVC response. All vasoactive stimuli produced the largest diameter changes at the first capillary that branches off from the penetrating arteriole. Our results reveal that three different signaling pathways mediate the effects of NO, ET1 and KATP channels on brain pericytes and capillary blood flow by mechanisms similar to vascular smooth muscle despite great differences in morphology.

neuroscience↗

bioRxiv2019

Apolipoprotein M-bound sphingosine-1-phosphate regulates blood-brain barrier paracellular permeability and transcytosis

ABTRACTThe blood-brain barrier (BBB) is formed by the endothelial cells lining cerebral microvessels. Here, we report that the BBB permeability is modified by apolipoprotein M (apoM)-bound sphingosine 1-phosphate (S1P). We used two-photon microscopy to monitor changes in BBB permeability in apoM-deficient mice (apoM-/-), showing significant increases in paracellular BBB permeability to small molecules without structural changes in junctional complexes between endothelial cells. Lack of apoM-bound S1P increased vesicle-mediated transfer of albumin across endothelium of brain pial and penetrating arterioles, whereas transcytosis in capillaries and venules remained unchanged. S1PR1 agonist SEW2871 rapidly normalized BBB permeability along both the paracellular and transcellular routes in apoM-/- mice. Thus, apoM-bound S1P maintains low paracellular BBB permeability for small molecules in all cerebral microvessels and low levels of adsorptive transcytosis in penetrating arterioles. Modulation of apoM/S1P-dependent signaling may be a novel strategy for the protection of brain endothelial cells to preserve the BBB function.

neuroscience↗

bioRxiv2019

Sensory Stimulation-Induced Astrocytic Calcium Signaling in Electrically Silent Ischemic Penumbra

Middle cerebral artery occlusion (MCAO) induces ischemia characterized by a densely ischemic focus, and a less densely ischemic penumbral zone in which neurons and astrocytes display age-dependent dynamic variations in spontaneous Ca2+ activities. However, it is unknown whether penumbral nerve cells respond to sensory stimulation early after stroke onset, which is critical for understanding stimulation-induced stroke therapy. In this study, we investigated the ischemic penumbras capacity to respond to somatosensory input. We examined adult (3- to 4-month-old) and old (18- to 24-month-old) male mice at 2-4 hours after MCAO, using two-photon microscopy to record somatosensory stimulation-induced neuronal and astrocytic Ca2+ signals in the ischemic penumbra. In both adult and old mice, MCAO abolished spontaneous and stimulation-induced electrical activity in the penumbra, and strongly reduced stimulation-induced Ca2+ responses in neuronal somas (35-82%) and neuropil (92-100%) in the penumbra. In comparison, after stroke, stimulation-induced astrocytic Ca2+ responses in the penumbra were only moderately reduced (by 54-62%) in adult mice, and were even better preserved (reduced by 31-38%) in old mice.\n\nOur results suggest that somatosensory stimulation evokes astrocytic Ca2+ activity in the ischemic penumbra. We hypothesize that the relatively preserved excitability of astrocytes, most prominent in aged mice, may modulate protection from ischemic infarcts during early somatosensory activation of an ischemic cortical area. Future neuroprotective efforts in stroke may target spontaneous or stimulation-induced activity of astrocytes in the ischemic penumbra.

neuroscience↗

bioRxiv2019

Modification of oxygen consumption and blood flow in mouse somatosensory cortex by cell-type-specific neuronal activity

Gamma activity arises from the interplay between pyramidal neurons and fast-spiking parvalbumin (PV) interneurons, is an integral part of higher cognitive functions and is assumed to contribute importantly to brain metabolic responses. Cerebral metabolic rate of oxygen (CMRO2) responses were evoked by optogenetic stimulation of cortical PV interneurons and pyramidal neurons. We found that CMRO2 responses depended on neuronal activation, but not on the power of gamma activity induced by optogenetic stimulation. This implies that evoked gamma activity per se is not energy demanding. Optogenetic stimulation of PV interneurons during somatosensory stimulation reduced excitatory neuronal activity but did not potentiate O2 consumption as previously hypothesized. In conclusion, our data suggest that activity-driven CMRO2 responses depend on neuronal excitation rather than the cerebral rhythmic activity they induce. Excitation of both excitatory and inhibitory neurons requires energy, but inhibition of cortical excitatory neurons by interneurons does not potentiate activity-driven energy consumption.

neuroscience↗

bioRxiv2017

A comprehensive profile of circulating RNAs in human serum

Non-coding RNA (ncRNA) molecules have fundamental roles in cells and many are also stable in body fluids as extracellular RNAs. In this study, we used RNA sequencing (RNA-seq) to investigate the profile of small non-coding RNA (sncRNA) in human serum. We analyzed 10 billion lllumina reads from 477 serum samples, included in the Norwegian population-based Janus Serum Bank (JSB). We found that the core serum RNA repertoire includes 258 micro RNAs (miRNA), 441 piwi-interacting RNAs (piRNA), 411 transfer RNAs (tRNA), 24 small nucleolar RNAs (snoRNA), 125 small nuclear RNAs (snRNA) and 123 miscellaneous RNAs (misc-RNA). We also investigated biological and technical variation in expression, and the results suggest that many RNA molecules identified in serum contain signs of biological variation. They are therefore unlikely to be random degradation by-products. In addition, the presence of specific fragments of tRNA, snoRNA, Vault RNA and Y_RNA indicates protection from degradation. Our results suggest that many circulating RNAs in serum can be potential biomarkers.

bioinformatics↗