Melhem, S. | Search bioRxiv

bioRxiv2026

Localisation of corticosteroids in male mouse kidney by mass spectrometry imaging

Renal sodium balance is important for blood pressure homeostasis and is regulated by corticosteroids, chiefly aldosterone but also glucocorticoids. Abundance of these hormones in functional subregions of the kidney is unknown, previous work being limited to measurements in plasma and urine, and in microdialysate from kidney medulla. Here mass spectrometry imaging (MSI) was applied to map corticosteroids in kidney to understand how their distribution overlays with functional targets. Male C57BL6 mice, aged 10 weeks, were fed diets containing 0.03%, 0.3% or 3% w:w sodium for two weeks and kidneys harvested at cull. Steroids were localised as Girard T derivatives on cryosections using Matrix assisted laser desorption ionisation Fourier transform ion cyclotron MSI, with confirmation by liquid extraction surface analysis. Co-registration was performed on sections stained with hematoxylin and eosin. Corticosterone localised along the papilla, medulla and inner cortex, whereas 11-dehydrocorticosterone was concentrated in the medulla. Higher amounts of aldosterone were present in medulla and outer cortex. Distribution patterns were unchanged by dietary salt, but amounts of corticosterone were elevated, particularly in outer cortex with low salt diet. MSI holds great promise to dissect corticosteroid signalling in functional zones of the kidney.

biochemistry↗

bioRxiv2022

FTD-tau S320F mutation stabilizes local structure and allosterically promotes amyloid motif-dependent aggregation

Amyloid deposition of the microtubule-associated protein tau is a unifying theme in a multitude of neurodegenerative diseases. Disease-associated missense mutations in tau are associated with frontotemporal dementia (FTD) and enhance tau aggregation propensity. However, the molecular mechanism of how mutations in tau promote tau assembly into amyloids remains obscure. There is a need to understand how tau folds into pathogenic conformations to cause disease. Here we describe the structural mechanism for how an FTD-tau S320F mutation drives spontaneous aggregation. We use recombinant protein and synthetic peptide systems, computational modeling, cross-linking mass spectrometry, and cell models to investigate the mechanism of spontaneous aggregation of the S320F FTD-tau mutant. We discover that the S320F mutation drives the stabilization of a local hydrophobic cluster which allosterically exposes the 306VQIVYK311 amyloid motif. We identify a suppressor mutation that reverses the S320F aggregation phenotype through the reduction of S320F-based hydrophobic clustering in vitro and in cells. Finally, we use structure-based computational design to engineer rapidly aggregating tau sequences by optimizing nonpolar clusters in proximity to the S320 site revealing a new principle that governs the regulation of tau aggregation. We uncover a mechanism for regulating aggregation that balances transient nonpolar contacts within local protective structures or in longer-range interactions that sequester amyloid motifs. The introduction of a pathogenic mutation redistributes these transient interactions to drive spontaneous aggregation. We anticipate deeper knowledge of this process will permit control of tau aggregation into discrete structural polymorphs to aid design of reagents that can detect disease-specific tau conformations.

biophysics↗