Exploring [11C]CPPC as a CSF1R-targeted PET Imaging Marker for Early Parkinson's Disease Severity

Abstract

Neuroinflammation through enhanced innate immunity is thought play a role in the pathogenesis of Parkinson's disease (PD). Methods for monitoring neuroinflammation in living patients with PD are currently limited to positron emission tomography (PET) ligands that lack specificity in labeling immune cells in the nervous system. The colony stimulating factor 1 receptor (CSF1R) plays a crucial role in microglial function, an important cellular contributor to the nervous system's innate immune response. Using immunologic methods, we show that CSF1R in human brain is colocalized with the microglial marker, ionized calcium binding adaptor molecule 1 (Iba1). In PD, CSF1R immunoreactivity is significantly increased in PD across multiple brain regions, with the largest differences in the midbrain versus controls. Autoradiography revealed significantly increased [³H]JHU11761 binding in the inferior parietal cortex of PD patients. PET imaging demonstrated that higher [¹¹C]CPPC binding in the striatum was associated with greater motor disability in PD. Furthermore, increased [¹¹C]CPPC binding in various regions correlated with more severe motor disability and poorer verbal fluency. This study finds that CSF1R expression is elevated in PD and that [¹¹C]CPPC-PET imaging of CSF1R is indicative of motor and cognitive impairments in the early stages of the disease. Moreover, the study underscores the significance of CSF1R as a promising biomarker for neuroinflammation in Parkinson's disease, suggesting its potential use for non-invasive assessment of disease progression and severity, leading to earlier diagnosis and targeted interventions.

Keywords: Biological Sciences; Neuroscience; Parkinson’s disease; microglia; neuroinflammation.

Figure 1.

Increased levels of CSF1R in brains of human PD patients. (A) Representative confocal images with DAPI(blue), IBA1(green) and CSF1R(red) in the Midbrain and Cingulate cortex of age-matched healthy control and PD patients. White dashed lines demark the region from where high-magnification images were generated. Scale bars, 200μm (low-magnification images) and 50μm (high-magnification images). (B) CSF1R+ cells with IBA1+ cells are quantified. n = 4 biologically independent sample. Data are shown as the mean ± SEM. p values were determined by unpaired two-tailed Student’s t-tests. *p < 0.05, versus healthy control. (C) Representative immunoblots with CSF1R and β-actin antibodies in the Midbrain (MB), Cingulate cortex (Cing), Posterior cingulate cortex (Post), Temporal cortex (Temp), Cerebellar cortex (CB) and Caudate (Caud) of age-matched healthy control and PD patients. (D) Relative CSF1R levels normalized to β -actin was quantified. n = 4 biologically independent sample. Data are shown as the mean ± SEM. p values were determined by unpaired two-tailed Student’s t-tests. *p < 0.05, **p < 0.005, ***p < 0.0005, versus healthy control.

Figure 2.

In vitro CSF1R autoradiography with ³H-JHU11761 in human inferior parietal cortex with and without Parkinson’s disease. Labels show diagnosis of Parkinson’s disease (PD) or C (control) with donor age and sex. Tritium scales standards on the left depict densities beginning at 5.89 nmol/g (1) and serially decrease until (7), 0.09 nmol/g. Grey matter B_max is indicated to the left of each case. PD age range 65–72. Control age range 90–97.

Figure 3.

B_max of ³H-JHU11761 from human frozen sections of A) inferior parietal cortex grey matter (IPCGM) and white matter (IPCWM), and B) white matter and C) grey matter B_max in the caudate nucleus (CN), midbrain (MB), and basal ganglia (BG). IPCGM and IPCWM shown separately due to difference in y-axis scale. *p<0.05.

Figure 4.

Regional total volume of distribution (V_T) of [¹¹C]CPPC, a CSF1R PET radioligand, in people with mild or moderate PD, defined by motor disability, and controls of a similar age. * = p<0.05 and ** = p<0.004 for ANOVA and post-hoc test between Moderate PD vs. Mild PD and or Moderate PD vs. healthy controls. ACC = anterior cingulate cortex, CBx = cerebellar cortex, FC = frontal cortex, Hp = hippocampus, OC = occipital cortex, PC = parietal cortex, PCC = posterior cingulate cortex, Str = striatum, TC = temporal cortex, Th = thalamus. Dot = outliers.

Figure 5.

Scatter plots and linear relationship between [¹¹C]CPPC V_T and ADL disability from motor symptoms, measured by MDS-UPDRS Part II in regions of interest that showed a statistically significant relationship (p<0.005).