Biology subjects

Hoekstra, M.

Publications and source records attributed to Hoekstra, M..

4 recordsLinked to original sources

bioRxiv2025

Presynaptic Release Probability Determines the Need for Sleep

Sleep is universal among animals with synapses, yet the synaptic functions determining the need for sleep remain elusive. By directly measuring synaptic transmission at anatomically defined synapses in Drosophila, we found that synaptic strength remained stable or declined after sleep deprivation in a circuit-specific manner. In contrast, presynaptic release probability (Pr) consistently decreased with sleep loss across circuits and species, stemming from reduced Ca2+ influx or weakened vesicle-channel coupling at presynaptic terminals, and recovered after sleep. Bidirectional manipulations of Pr altered sleep pressure, establishing a causal relationship between presynaptic function and sleep need. Non-synaptic sleep-regulatory signaling pathways consistently modulate Pr but not synaptic strength. Thus, our findings identify Pr, rather than synaptic strength, as the conserved synaptic substrate underlying sleep need.

neuroscience↗

bioRxiv2025

Increased numbers of CD4+ T-cells in hypocretin/orexin region of Narcolepsy Type 1

Narcolepsy type 1 (NT1) is proposed to be an autoimmune disorder targeting hypothalamic hypocretin (orexin, Hcrt) neurons. Hcrt reactive T-cells have been identified in blood and cerebrospinal fluid (CSF) of NT1 patients. However, it remains unknown whether T-cells infiltrate the brain. Since T-cells can be retained for a lifetime in tissues as tissue resident memory T-cells after primary antigen exposure, we now systematically assess the presence of CD4+ and CD8+ T-cells in NT1 brains to determine their regional distribution and potential autoimmune involvement in NT1 neuropathology. We immunohistochemically stained and quantified CD4+ and CD8+ T-cells in post-mortem brain tissue of NT1 patients (n=5) and matched controls (n=5) in the Hcrt region, paraventricular nucleus (PVN) and median eminence (ME) as well as in the substantia nigra (SN) and locus coeruleus (LC). To phenotypically characterize CD4+ T-cells, we performed double staining with CD49a or C-X-C chemokine receptor type 6 (CXCR6). Furthermore, we stained for fibrinogen to estimate blood-brain barrier integrity, as well as microglia markers and an astrocyte marker to evaluate acute immune reactivity in the Hcrt region of NT1 brains. In NT1 there was an 11-fold increase in total number of CD4+ T-cells in the Hcrt region, but not in the PVN, ME, nor SN or LC. These CD4+ T-cells exhibited tissue residential memory features with double staining with CD49a or CXCR6. There were no changes in blood-brain barrier integrity, microglia and astrocyte staining intensities between NT1 and controls. In addition, the total number of CD4+ T-cells in the Hcrt region showed significant negative correlations with mean sleep latency in NT1 cases. Our findings suggest an enrichment of CD4+ T-cells specifically in the Hcrt region of NT1 indicating prior local antigen engagement. Moreover, greater CD4+ T-cell presence in the Hcrt region of NT1 was associated with increased symptom severity, as reflected by shorter sleep latency. These data support the hypothesis that CD4+ T-cells infiltrate the Hcrt region, where they may contribute to the autoimmune process that initiates NT1.

neuroscience↗

bioRxiv2024

Neuronal autophagosomes are transported to astrocytes for degradation

Autophagy is a vital catabolic process responsible for the degradation of cytosolic components, playing a key role in cellular homeostasis and survival. At synapses, autophagy is crucial for regulating neuronal activity and utilizes a specialized machinery. While considerable progress has been made in understanding the initiation of autophagy and autophagosome formation, the mechanisms governing the clearance of autophagosomes from synaptic sites remain poorly understood. Here, we identify a novel pathway in which astrocytes actively participate in the clearance of pre-synaptic autophagosomes. Using neurons derived from human induced pluripotent stem cell (hiPSC) lines expressing fluorescent autophagy markers and chimeric mouse models, we demonstrate that neuronal autophagosomal vesicles are physically transferred to astrocytes, a process that is enhanced when synaptic activity is suppressed. Autophagosome transfer does not require direct physical cellular contact, but it does require Dynamin and cholesterol-dependent endocytosis for the internalized neuronal autophagosomes to ultimately fuse with astrocytic lysosomes. Our findings reveal a previously unrecognized mechanism of neuronal autophagosome clearance that does not require slow axonal retrograde transport but their transfer to nearby astrocytes.

neuroscience↗

bioRxiv2022

Time to run: Late rather than early exercise training in mice remodels the gut microbiome and reduces atherosclerosis development

The metabolic and inflammatory processes that are implicated in the development of cardiovascular diseases are under control of the biological clock. While skeletal muscle function exhibits circadian rhythms, it is unclear to what extent the beneficial health effects of exercise are restricted to unique time windows. We aimed to study whether the timing of exercise training differentially modulates the development of atherosclerosis and elucidate underlying mechanisms. We endurance-trained atherosclerosis-prone female APOE*3-Leiden.CETP mice fed a Western-type diet, a well-established human-like model for cardiometabolic diseases, for one hour five times a week for four weeks either in their early or in their late active phase on a treadmill. We monitored metabolic parameters, the development of atherosclerotic lesions in the aortic root and assessed the composition of the gut microbiota. Late, but not early, exercise training reduced fat mass by 19% and the size of early-stage atherosclerotic lesions by as much as 29% compared to sedentary animals. No correlation between cholesterol exposure and lesion size was evident, as no differences in plasma lipid levels were observed, but circulating levels of the pro-inflammatory markers ICAM-1 and VCAM-1 were reduced with late exercise. Strikingly, we observed a time-of-day-dependent effect of exercise training on the composition of the gut microbiota as only late training increased the abundance of gut bacteria producing short-chain fatty acids with proposed anti-inflammatory properties. Together, these findings indicate that timing is a critical factor to the beneficial anti-atherosclerotic effects of exercise with a great potential to further optimize training recommendations for patients.

physiology↗