Pieterjan Van Maele

Background/Objectives. VHHs (Nanobodies^®) are camelid single-domain antibody fragments with broad applicability in central nervous system (CNS) research, including blood–brain barrier transport, modulation of pathological proteins and molecular detection. However, few VHHs have been developed for cell-type-specific targeting within the brain. Astrocytes play essential roles in CNS homeostasis and contribute to many neurological disorders, making them an appealing target for diagnostic and therapeutic approaches. Here, we report the development and validation of the first VHHs directed against the astrocyte-enriched glutamate transporters GLT-1 and GLAST-1. Methods. VHHs were generated from a camelid immune library using phage display. Target specificity and affinity were evaluated in cells overexpressing the mouse and human transporters, as well as in iPSC-derived astrocytes. Target engagement and astrocyte specificity was further assessed ex vivo on brain sections using immunohistochemistry and in dissociated mouse brain cell suspensions by flow cytometry. VHH in vivo binding was evaluated by stereotactic injections within the brain striatum. Results. One anti-GLT-1 VHH and four anti-GLAST-1 VHHs demonstrated high specificity and apparent nanomolar affinity when binding tocells overexpressing the mouse transporters. The anti-GLT-1 VHH was additionally cross-reactive with the human ortholog, as demonstrated in overexpressing cells and iPSC-derived astrocytes. All VHHs showed target engagement on mouse brain sections and astrocyte specificity in dissociated mouse brain cell suspensions. VHH direct brain delivery resulted in localized transporter-specific signal around the injection site, whereas the non-binding isotype control VHH produced no detectable signal. Conclusions. Here we present the first set of VHHs capable of selectively recognizing astrocyte-enriched glutamate transporters GLT-1 and GLAST-1 in vitro, ex vivo, and in vivo. These VHHs constitute promising tools for astrocyte detection in research applications and the cross-reactive anti-GLT-1 lead might hold potential for future diagnostic or therapeutic strategies, including cell-targeted payload delivery.

Background and objectives: The PWWP domain of lens epithelium-derived growth factor p75 (LEDGF/p75) mediates chromatin engagement through recognition of histone H3 lysine 36 di- and trimethylation (H3K36me2/3) and nucleosomal DNA. LEDGF/p75 plays a role in multiple human diseases. In particular, its interaction with HIV-1 integrase enables viral genome integration. However, the LEDGF PWWP domain remains difficult to target with small molecules as it lacks optimally shaped binding pockets. Here, we report the generation of high-affinity nanobodies (Nbs) to investigate the structure and function of this domain. Methods: Camelids were immunized with recombinant LEDGF PWWP domain, and immune phage display libraries were screened for affinity. Selected Nbs were recombinantly expressed in E. coli and purified. Their interaction with the PWWP domain of LEDGF and its close homolog HRP-2 was characterized using size-exclusion chromatography and surface plasmon resonance. Structural characterization of the Nbs was performed using X-ray crystallography. Functional effects on chromatin engagement were evaluated using an AlphaScreen assay. Results: Nine sequence-distinct Nbs were identified, seven of which were confirmed to bind the LEDGF PWWP domain with nanomolar affinities. Five Nbs also bound the HRP-2 domain, consistent with conserved functional surfaces, while two showed reduced affinity. The crystal structures of two Nbs (NbC03 and NbH10) confirmed there were canonical immunoglobulin folds, while the latter additionally revealed a domain-swapped dimer. Moreover, NbH10 dose-dependently inhibited the interaction between full-length LEDGF/p75 and H3K36me3-modified nucleosomes in vitro. Conclusions: This work establishes a validated panel of Nbs targeting the LEDGF PWWP domain and identifies one Nb capable of functionally disrupting the LEDGF–chromatin interaction. These Nbs serve as valuable tools for functional studies and structure-based drug design.

Background and objectives: The PWWP domain of lens epithelium-derived growth factor p75 (LEDGF/p75) mediates chromatin engagement through recognition of histone H3 lysine 36 di- and trimethylation (H3K36me2/3) and nucleosomal DNA. LEDGF/p75 plays a role in multiple human diseases. In particular, its interaction with HIV-1 integrase enables viral genome integration. However, the LEDGF PWWP domain remains difficult to target with small molecules as it lacks optimally shaped binding pockets. Here we report the generation of high-affinity nanobodies (Nbs) to investigate the structure and function of this domain. Methods: Camelids were immunized with recombinant LEDGF PWWP domain, and immune phage display libraries were screened for affinity. Selected Nbs were recombinantly expressed in E. coli and purified. Their interaction with the PWWP domain of LEDGF and its close homolog HRP-2 was characterized using size-exclusion chromatography and surface plasmon resonance. Structural characterization of the Nbs was performed by X-ray crystallography. Functional effects on chromatin engagement were evaluated using the AlphaScreen assay. Results: Nine sequence-distinct Nbs were identified, seven of which were confirmed to bind the LEDGF PWWP domain with nanomolar affinities. Five Nbs also bound the HRP-2 domain, consistent with conserved functional surfaces, while two showed reduced affinity. Crystal structures of two Nbs (NbC03 and NbH10) confirmed canonical immunoglobulin folds, while the latter additionally revealed a domain-swapped dimer. Moreover, NbH10 dose-dependently inhibited the interaction between full-length LEDGF/p75 and H3K36me3-modified nucleosomes in vitro. Conclusions: This work establishes a validated panel of Nbs targeting the LEDGF PWWP domain and demonstrates their ability to functionally disrupt the LEDGF-chromatin interaction. These Nbs serve as valuable tools towards functional studies and structure-based drug design.