Biology subjects

Hultqvist, G.

Publications and source records attributed to Hultqvist, G..

4 recordsLinked to original sources

bioRxiv2026

Paralemmin-2 is a membrane-anchored cytoskeletal constituent of Axon Initial Segments and nodes of Ranvier

The axon initial segment (AIS) and nodes of Ranvier (NoR) are essential for action potential initiation and propagation. They share many features of their molecular architecture, and their assembly mechanisms converge on the membrane-associated periodic skeleton (MPS). Here, we identify Paralemmin-2 (Palm2) as a component of both the AIS and NoR. Palm2 depletion shortens the AIS and reduces neuronal excitability. Endogenous Palm2 in the AIS is non-periodic, but upon overexpression it associates with the MPS, localizing to actin rings and reducing {beta}IV-spectrin abundance and periodicity. In NoR of the central and peripheral nervous system, Palm2 localizes to different subdomains - nodal or paranodal, respectively. Palm2, and its homolog Palm1, bind the deubiquitinase USP7, implicating paralemmins in proteostasis at the MPS. The complementary localizations of Palm2 and Palm1 at the AIS/NoR or axon shafts, respectively, parallel the distributions of {beta}-spectrin and ankyrin isoforms between these axonal compartments. We propose that Palm2 modulates the submembrane cytoskeleton and its membrane attachment, and thus contributes to the assembly, functioning and remodeling of the AIS and NoR.

cell biology↗

bioRxiv2025

Engineered Fab glycosylation of a blood-brain barrier transporter single-chain variable fragment preserved functionality but did not impact anti-drug antibody formation

The single-chain variable fragment (scFv) of the 8D3 antibody enables blood-brain barrier transport via transferrin receptor-mediated transcytosis. However, when fused to therapeutic antibodies, scFv8D3 increased immunogenicity and triggered anti-drug antibodies (ADA). Sialylation of N-linked glycans can critically influence protein immunogenicity, potentially conferring immunosuppressive properties and extended half-life. We investigated whether introducing sialic acid residues to scFv8D3 through engineered fragment antigen-binding (Fab) glycosylation could reduce ADA formation. We generated two novel variants with distinct N-linked glycosylation motifs (NXT/S), which both displayed sialic acid residues and retained functionality, as evidenced by the preservation of transferrin receptor binding and brain uptake. However, Fab glycosylation did not significantly alter pharmacokinetics or ADA production in mice. Our findings demonstrated that introducing Fab glycosylation is feasible, without compromising biological activity. Nonetheless, this strategy alone was insufficient to mitigate immunogenicity, underscoring the need for alternative approaches to improve the long-term safety of brain-targeting therapeutics. Statement of significanceSialylation of N-linked glycans can critically influence protein immunogenicity. We introduced N-linked Fab glycosylation sites into a scFv-based therapeutic construct with the aim of reducing ADA production upon repeated administration to mice. Although the sialylated variants retained functionality, pharmacokinetics and ADA levels remained unaffected, suggesting limited immunomodulation via engineered sialylation.

bioengineering↗

bioRxiv2025

Paralemmin-3 sustains the integrity of the lateral plasma membrane and subsurface cisternae of auditory hair cells

In the mammalian inner ear, cochlear inner hair cells (IHCs) enable accurate and faithful synaptic sound encoding, while outer hair cells (OHCs) perform frequency-specific sound amplification and fine-tuning through their intrinsic voltage-dependent somatic electromotility. This latter process is facilitated by the unique trilaminate structure of the OHC lateral wall, which consists of the plasma membrane that is densely occupied by the transmembrane motor protein Prestin, the submembrane actin- and spectrin-based cytoskeleton, and the endomembranous subsurface cisternae. This complex system provides mechanical resilience while allowing for cell expansion and contraction during electromotility. Whereas the ultrastructure of the lateral wall is well described, its molecular architecture remains largely elusive. Here, we identified Paralemmin-3 (Palm3) as a novel protein specifically localized to the lateral walls of auditory HCs to play a crucial role in connecting the plasma membrane to the underlying cytoskeleton and subsurface cisternae. Palm3-KO mice display early-onset and progressive hearing impairment that results from diminished cochlear amplification. Subsequent multiscale morphological analyses revealed structural collapse of OHCs that led to progressive and extensive OHC loss along the tonotopic axis. Palm3-KO OHCs exhibited disrupted expression and distribution of several membrane-associated proteins - including spectrin isoforms and Prestin - suggesting an essential role of Palm3 in plasma membrane scaffolding. Electron tomography of OHC lateral walls revealed significantly fewer and structurally perturbed subsurface cisternae. Finally, adeno-associated virus (AAV)-mediated rescue of Palm3 during early postnatal development partly restored hearing function, enhanced OHC survival, and restored OHC cell shape as well as membrane protein expression levels. In summary, Palm3 is a key component of the submembrane cytoskeleton in cochlear hair cells, playing a fundamental role in hair cell biology and hearing, and emerges as an attractive candidate for the long-elusive "pillar" component of the hair cell lateral wall ultrastructure.

cell biology↗

bioRxiv2023

Effect of ketamine on early synaptic mistuning and emotional behavior deficits in AppNL-F mouse model of Alzheimer's disease.

Alzheimers disease is the most common neurodegenerative disease and constitute 75% of dementia cases worldwide. Unfortunately, efficient and affordable treatments are still lacking for this mental illness, it is therefore urgent to identify new pharmacological targets. Whereas the late phases of the disease are well described, recent evidence suggest synaptic impairments at a pre-amyloid {beta} (A{beta}) plaque stage. Astrocytes are playing a crucial role in the tuning of synaptic transmission and several studies have pointed out severe astrocyte reactivity in Alzheimers disease, especially around A{beta} plaques. Reactive astrocytes show altered physiology and function, suggesting they could have a role in the early pathophysiology of Alzheimers disease. In this study we used the AppNL-F knock-in mouse model of Alzheimers disease which carries two disease-causing mutations inserted in the amyloid precursor protein (App) gene. This strain does not start to develop A{beta} plaques until nine months of age. To better understand early changes in Alzheimers disease, we investigated synaptic function, at both neuronal and astrocytic levels, in six months old AppNL-F mice and correlate the synaptic dysfunction with emotional behavior. Electrophysiological recordings in the hippocampus revealed an overall synaptic mistuning at a pre-plaque stage of the pathology, associated to an intact social memory but a stronger depressive-like behavior. Astrocytes displayed a reactive-like morphology and a higher tonic GABA current compared to control mice. Interestingly, we here show that the synaptic impairments in hippocampal slices are partially corrected by a pre-treatment with the monoamine oxidase B (MAO-B) blocker deprenyl or the fast-acting antidepressant ketamine (5mg/kg). Thus, we propose that reactive astrocytes can induce synaptic mistuning early in Alzheimers disease, before plaques deposition, and that these changes are associated with emotional symptoms. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=144 SRC="FIGDIR/small/540486v2_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@fb19a7org.highwire.dtl.DTLVardef@151454borg.highwire.dtl.DTLVardef@9c7a12org.highwire.dtl.DTLVardef@112633e_HPS_FORMAT_FIGEXP M_FIG GRAPHICAL ABSTRACT C_FIG

neuroscience↗