The olfactory bulb proteotype differs across frontotemporal dementia spectrum.

Mild olfactory dysfunction has been observed in frontotemporal dementias (FTD). However, the underlying molecular mechanisms associated to this deficit are poorly understood. We applied quantitative proteomics to analyze pathological effects on the olfactory bulb (OB) from progressive supranuclear palsy (PSP) and frontotemporal lobar degeneration (FTLD-TDP43) subjects respect to elderly non-FTD group. Our data revealed: i) a mitochondrial and calcium homeostasis impairment in PSP and ii) a disruption of protein synthesis and vesicle trafficking in FTLD-TDP43. Although differential OB proteomes clearly differ between both FTD phenotypes, functional analyses pointed out an imbalance in survival signaling in both pathologies. A common alteration of olfactory mitogen-activated protein kinases (MAPKs), calcium/calmodulin dependent protein kinase II (CAMKII), and protein kinase C (PKC) signaling pathways was observed in PSP and FTLD subjects. In contrast, a specific shut off in mitogen-activated protein kinase kinase 4 (SEK1/MKK4)/stress-activated protein kinase (SAPK) axis was exclusively observed in PSP, whereas a specific phosphoinositide-dependent protein kinase 1 (PDK1) inactivation was observed in FTLD-TDP43. In summary, our data contribute to a better understanding of the molecular mechanisms that are modulated in PSP and FTLD-TDP43 at olfactory level, highlighting cross-disease similarities and differences in the regulation of survival pathways across FTD spectrum. SIGNIFICANCE: This work reflects differential olfactory molecular disarrangements in PSP and FTLD-TDP43, two clinically similar FTD disorders, but with different neuropathological signature. Besides FTDs present mild olfactory dysfunction, our data provide basic information for understanding the implication of the OB in the pathophysiology of FTDs.