Altered brain energy metabolism related to astrocytes in tauopathies

Abstract

AbstractBackgroundAccumulated evidence suggests altered energy metabolism in the brain of tauopathies. In Alzheimer’s disease (AD) and progressive supranuclear palsy (PSP), decreased fluorodeoxyglucose (FDG) uptake in the cingulate cortex is considered a marker of neurodegeneration. However, its underlying pathogenesis remains unknown. It is hypothesized that lactate, a glucose metabolite, is produced in astrocytes and subsequently shuttles to neurons as an energy substrate. The current study aims to examine alterations in lactate and glucose concentrations and their association with astrocytic activities in the cingulate cortex of patients with AD and PSP.MethodThirty AD, 30 PSP, and 30 healthy control (HC) subjects were enrolled. Lactate, glucose, and myoinositol (mI), an astroglial marker, in the anterior cingulate cortex (ACC) and posterior cingulate cortex (PCC) were determined by magnetic resonance spectroscopy (MRS) (3T scanner, SPECIAL sequence, TR/TE 3000/8.5ms, LCModel analysis) (Figure 1). Tau depositions were assessed using PET imaging with 18F‐PM‐PBB3.ResultAll the patients with AD and PSP were confirmed to have the typical distribution of tau pathology. Lactate, glucose, and mI levels were higher in the ACC in PSP and AD, and PCC in AD compared to HC (p < 0.05) (Figure 2). In these cortical regions, lactate levels showed a positive correlation with mI levels (p < 0.05) (Figure 3). Lactate levels in the PCC in AD patients showed a positive correlation with Clinical Dementia Rating‐Sum of Boxes (CDR‐SB) scores (p < 0.05) (Figure 4). Moreover, mI levels in the ACC in PSP patients were negatively correlated with Frontal Assessment Battery (FAB) scores (p < 0.05) (Figure 4).ConclusionWe found elevated lactate and glucose levels accompanied by an increased astroglial marker mainly in the PCC in AD and ACC in PSP patients. Moreover, elevated lactate and mI levels in the cingulate cortex reflected the cognitive decline of AD and PSP, respectively. The excess lactate and glucose levels in the disease‐specific regions might reflect decreased energy utilization as shown in previous FDG‐PET studies. Given the residual lactate levels were correlated with mI levels, we speculated that the impaired lactate shuttle of reactivated astrocytes disrupts energy metabolism, leading to cognitive dysfunctions.