Mixed pathologies in pancreatic β cells from subjects with neurodegenerative diseases and their interaction with prion protein

Abstract

Protein misfolding diseases refer to a variety of disorders that develop as a consequence of the misfolding of proteins in various organs. The etiologies of Parkinson's and Alzheimer's disease remain unclear, but it seems that type two diabetes and other prediabetic states could contribute to the appearance of the sporadic forms of these diseases. In addition to amylin deposition, other amyloidogenic proteins implicated in the pathophysiology of neurodegenerative diseases could have important roles in the pathogenesis of this disease. As we have previously demonstrated the presence of α-synuclein deposits in the pancreas of patients with synucleinopathies, as well as tau and Aβ deposits in the pancreatic tissue of Alzheimer's disease patients, we studied the immunoreactivity of amylin, tau and α-synuclein in the pancreas of 138 subjects with neurodegenerative diseases or type two diabetes and assessed whether the pancreatic β-cells of these subjects present cooccurrence of misfolded proteins. Furthermore, we also assessed the pancreatic expression of prion protein (PrP) in these subjects and its interaction, both in the pancreas and brain, with α-synuclein, tau, Aβ and amylin. Our study shows, for the first time, that along with amylin, pancreatic α-synuclein, Aβ, PrP and tau may contribute together to the complex pathophysiology of type two diabetes and in the appearance of insulin resistance in Alzheimer's and Parkinson's disease. Furthermore, we show that the same mixed pathologies that are observed in the brains of patients with neurodegenerative diseases are also present outside the nervous system. Finally, we provide the first histological evidence of an interaction between PrP and Aβ, α-synuclein, amylin or tau in the pancreas and locus coeruleus. These findings will shed more light on the common pathological pathways shared by neurodegenerative diseases and type two diabetes, benefiting the exploration of common therapeutic strategies to prevent or treat these devastating amyloid diseases.

Keywords: Alpha-synuclein; Alzheimer’s disease; Parkinson’s disease; PrP; Tau; Type two diabetes mellitus.

Fig. 1

Amylin, α-synuclein, tau and PrP immunoreactivity in endocrine pancreatic cells. Immunohistochemistry for amylin (a–d), α-synuclein (e–h), Tau (i–l), and PrP (m–p) in pancreatic cells from subjects with a normal neuropathological examination and no history of T2DM (a, c, i, m), with a normal neuropathological examination and history of T2DM (b, f, j, n), with Parkinson`s disease (PD), dementia with Lewy bodies (DLB) or incidental Lewy body disease (ILBD) (c, g, k, o) or with Alzheimer’s disease (AD) (d, h, l, p): 40 × magnification; scale bar = 50 µm. Violin plots showing amylin (q), α-synuclein (r), Tau (s) and PrP^c (t) immunoreactivity quantification in endocrine pancreatic cells: **: p ≤ 0.05, ***: p ≤ 0.001; ****: p ≤ 0.0001

Fig. 2

α-synuclein deposition in pancreatic β cells of subjects with Alzheimer’s disease. Immunohistochemistry for serine 129-phosphorylated α-synuclein immunofluorescence (a) C-terminal cleaved α-synuclein (b) and nitrated α-synuclein (c) from a 70-year-old female with Alzheimer’s disease. α-synuclein PLA (d), with insulin immunofluorescence (e) and DAPI as nuclear counterstaining (f) from a 73-year-old female with Alzheimer’s disease. Serine 129-phosphorylated α-synuclein immunofluorescence (g) and thioflavin S fluorescence (h) in pancreatic β cells from a 77-year-old female with Alzheimer’s disease (i): 40 × magnification; scale bar = 50 µm

Fig. 3

Tau and Aβ inclusions in pancreatic β cells of subjects with Parkinson’s disease, Lewy body dementia and incidental Lewy body disease. Immunohistochemistry for Ser202-Thr205-phosphorylated tau (AT8) (a), Ser262-phosphorylated tau (b), Thr181-phosphorylated tau (AT270) (c), Thr212-Ser214-phosphorylated tau (AT100) (d), Thr231-phosphorylated tau (AT180) (e), Ser422-phosphorylated tau (f), Asp421-cleaved tau (g), tau Alz50 (h), tau MC-1 (i), endocrine oligomeric tau (j), exocrine oligomeric tau (k) and Aβ (l) inclusions in pancreatic cells from subjects with incidental Lewy body disease (a, b, c, f), Parkinson’s disease (d, e, g, h, i, l) and dementia with Lewy body (j, k): a 40 × magnification; scale bar = 50 µm

Fig. 4

PrP pancreatic expression characterization. Immunohistochemistry for PrP with (a–c) and without (d–f) proteinase K digestion in the pancreas from a subject with a normal neuropathological examination and history of T2DM (a, d), a subject with Parkinson’s disease (b, e) and with Alzheimer’s disease (c, f). Dual immunofluorescence for PrP^c and glucagon (g–i), somatostatin (j–l) or insulin (m–o) to assess the cellular localization of PrP in the pancreas from a 73-year-old female with Parkinson’s disease: 40 × magnification; scale bar = 50 µm

Fig. 5

In situ proximity ligation assays (PLA) on pancreatic β cells and the locus coeruleus. PLA for PrP and α-synuclein (a–aʺ), serine 129-phosphorylated α-synuclein (c–cʺ), tau (e–eʺ), oligomeric tau (g–gʺ), Aβ (i–iʺ), Aβ_1-42 (k–kʺ) or amylin (m–mʺ) with insulin immunofluorescence showed an interaction between these proteins in pancreatic β cells from a 73-year-old female with Parkinson’s disease (aʺ, cʺ) and from a 70-year-old male with Alzheimer’s disease (eʺ, gʺ, iʺ, kʺ, mʺ). Interactions between PrP and α-synuclein (bʹ, dʹ), tau (fʹ, hʹ), Aβ (jʹ, lʹ) or amylin (nʹ) were found in the locus coeruleus of the same subjects: DAPI nuclear counterstaining was used, 40 × magnification; scale bar = 50 µm