Biology subjects

Pirkmajer, S.

Publications and source records attributed to Pirkmajer, S..

5 recordsLinked to original sources

bioRxiv2026

β-Adrenergic inhibition of exocytotic surface deposition of MHCII molecules in reactive astrocytes is mediated by amisyn

Degeneration of the locus coeruleus, a noradrenergic nucleus, reduces noradrenaline bioavailability in the central nervous system and promotes neuroinflammation via reactive astrocytes, although the underlying mechanisms remain unclear. We investigated whether interferon-{gamma}-induced expression of major histocompatibility complex class II (MHCII), a marker of pro-inflammatory reactive astrocytes, is regulated by adrenergic receptors and amisyn. {beta}-Adrenergic, but not -adrenergic, stimulation increased cyclic adenosine monophosphate (cAMP) and reduced MHCII expression, as detected immunocytochemically, in human and rat astrocytes. {beta}-Adrenergic treatment altered transient exocytosis of lysosome-like vesicles, increasing event frequency and reducing fusion-pore conductance and dwell time, thereby limiting MHCII surface expression. Overexpression of wild-type amisyn inhibited surface expression of MHCII and the lysosomal marker CD63 and reduced fusion-pore conductance and dwell time. Conversely, amisyn knockdown enhanced full fusion exocytosis of larger vesicles and abolished {beta}-adrenergic effects, indicating that amisyn mediates {beta}-adrenergic inhibition of exocytosis and MHCII surface deposition.

neuroscience↗

bioRxiv2026

Intrinsic IL-6 expression reduces rhIL-6-induced JAK/STAT activation and promotes glucose and oleic acid oxidation in cultured human myoblasts

Interleukin-6 (IL-6), produced by skeletal muscle and extramuscular tissues, regulates skeletal muscle function through the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. However, the interaction between intrinsic (locally produced) IL-6 and extrinsic (circulating) IL-6 in skeletal muscle remains unclear. We investigated whether and how intrinsic expression of IL-6 in cultured primary human myoblasts influences their response to extrinsic stimulation with recombinant human IL-6 (rhIL-6). Using gene silencing, we found that suppression of intrinsic IL-6 enhanced rhIL-6-induced phosphorylation of STAT1 and STAT3. Silencing STAT3 also increased rhIL-6-induced STAT1 phosphorylation, but silencing STAT1 had no effect on STAT3 phosphorylation. Pretreatment of myoblasts with neutralising anti-IL-6 antibodies increased phosphorylation of STAT1 and STAT3 induced by 50 ng/mL rhIL-6, whereas pretreatment with 5 ng/mL rhIL-6 reduced this response. Despite increased JAK/STAT signalling, IL-6 silencing decreased glucose and oleic acid uptake and oxidation under both basal and rhIL-6-stimulated conditions. Collectively, our results imply that intrinsic IL-6 restrains activation of the JAK/STAT pathway by extrinsic IL-6, but acts synergistically with it to promote myoblast energy metabolism.

cell biology↗

bioRxiv2025

Low-load blood flow restriction training and ischemia modulate expression of Na+,K+-ATPase and FXYDs in human skeletal muscle

Anterior cruciate ligament (ACL) rupture leads to muscle deconditioning and downregulation of Na+,K+-ATPase (NKA). Low-load blood flow restriction (LL-BFR) training was shown to improve muscle function after ACL injury, but its effects on NKA are unknown. We analysed expression of NKA and its FXYD regulators in knee muscles from ACL-injured subjects undergoing LL-BFR, low-load training with sham blood flow restriction (LL-Sham), or no training (Control). Additionally, we dissected effects of ischemia components by subjecting cultured human myotubes to glucose deprivation and/or hypoxia. The LL-BFR group had higher vastus lateralis mRNA levels of NKA1, NKA{beta}3, and FXYD5 than the LL-Sham group. In vitro, NKA1, NKA{beta}1, and NKA{beta}3 mRNA and NKA1 and NKA{beta}1 protein levels were downregulated by sustained ischemia and glucose deprivation, but not hypoxia, while FXYD5 protein was upregulated by glucose deprivation. Conversely, intermittent ischemia had no effect on NKA or FXYD expression. In conclusion, our study shows that LL-BFR training induces specific transcriptional adaptations in vastus lateralis after ACL injury, potentially contributing to functional improvements. Moreover, it shows that glucose availability plays a major role in modulating NKA and FXYD expression in muscle cells under ischemic conditions. NEW & NOTEWORTHYO_LIThis is the first study exploring effects of low-load BFR training on Na+,K+-ATPase (NKA) and FXYD expression in knee muscles after anterior cruciate ligament injury. C_LIO_LIEffects of ischemia components were analysed by subjecting cultured human myotubes to glucose deprivation and/or hypoxia. C_LIO_LILL-BFR training induces specific transcriptional adaptations in vastus lateralis after ACL injury, potentially contributing to functional improvements. C_LIO_LIGlucose plays a major role in modulating NKA and FXYD expression in cultured myotubes under ischemic conditions. C_LI

physiology↗

bioRxiv2025

PDK1: one abbreviation, two kinases, relentless confusion

Despite peer review, hundreds of biomedical articles contain errors due to identical abbreviations that refer to different proteins. This includes PDK1, denoting both pyruvate dehydrogenase kinase 1 and 3-phosphoinositide-dependent protein kinase 1. Our analysis shows that one-out-of-five articles with the term PDK1 on PubMed, published in 2019-2026, state incorrect antibodies, refer to incorrect sequences for PCR, gene silencing, or plasmids, merge the properties of the two proteins, or incorrectly cite the other protein. Confusion extends to websites of biotechnology providers, where PDK1 antibodies and recombinant proteins were misattributed. To mitigate PDK1 abbreviation misuse, we recommend using unique protein abbreviations, clear antibody and sequence identification, and implementation of more rigorous peer review processes, supported by our newly developed PDK1-TermTracker citation network visualization and analysis service.

biochemistry↗

bioRxiv2018

Comparison of the effects of metformin on MDA-MB-231 breast cancer cells in a monolayer culture and in tumour spheroids as a function of nutrient concentrations

Metabolic pathways of cancer cells depend on the concentrations of nutrients in their micro-environment. However, they can vary also between monolayer cultures of cancer cells and tumour spheroids. Here we examined whether the absence of glucose, pyruvate and glutamine increases the sensitivity of MDA-MB-231 cells to metabolic drug metformin using two in vitro cell models (monolayer culture and tumour spheroids). To evaluate the effects of nutrient depletion in more detail, we tested the effects of metformin in commonly used media (DMEM, MEM and RPMI-1640) that differ mainly in the concentrations of amino acids. We used MTS, Hoechst and propidium iodide assay to determine cell number, viability and survival, respectively. We evaluated the effects of metformin on the size of tumour spheroids and determined cell survival by calcein and propidium iodide staining. Finally, we observed the effects of metformin in nutrient depleted conditions on the phosphorylation of AMP-activated protein kinase using Western blotting. Our main finding is that the effects of metformin on MDA-MB-231 cells depend on in vitro cell model used (monolayer culture vs. tumour spheroids). While metformin did not have any major effect on proliferation of MDA-MB-231 cells grown in complete cell culture media in a monolayer culture, it disintegrated tumour spheroids in MEM and RPMI-1640 medium. The effects of metformin on tumour spheroids were most pronounced in MEM, which is deficient of several non-essential amino acids. Glutamine depletion had no effect on the sensitivity of MDA-MB-231 cells to metformin in all tested conditions, whereas pyruvate depletion sensitized MDA-MB-231 cells to metformin in a monolayer culture only in MEM. Taken together, our results show that media formulation as well as in vitro cell model (monolayer culture vs. tumour spheroids) must be considered, when we evaluate the effects of metformin on MDA-MB-231 cells as a function of nutrient availability.

cancer biology↗