TMEM176B regulates phagosome maturation of glial cells and its increased activity contributes to the therapy of Alzheimer’s disease

Abstract Background Given recent interest in using amyloid b (Aβ)‐targeted antibodies as a therapy for patients with Alzheimer’s disease (AD), removal of Aβ by phagocytosis likely protective early in AD. Impaired phagocytic function of glial cells surrounding Aβ plaques during later stages in AD likely contributes to worsened disease outcomes, therefore enhancing phagocytic activity of glial cells could be a potent strategy for AD therapy. Method Changes in TMEM176B expression according to the progression of AD pathology was assessed by measuring TMEM176B protein in human AD brain lysates and TMEM176B transcripts in Ab‐treated primary rat astrocytes. The roles of TMEM176B in phagosome maturation of glial cells was investigated by measuring Rab5, Rab7, LAMP1, LAMP2, cathepsin D, and LC3B in presence of Aβ. Intracellular pH of glial cells was detected using fluorescent dye‐based pHrodo Red AM intracellular pH indicator (Invitrogen, Carlsbad, CA). In 5xFAD and 3xTg AD mice model, therapeutic effects of AAV‐TMEM176B was examined. AAV (adenovirus‐associated virus)‐TMEM176B (1 – 2×10 10 GC) was intracerebroventricularly injected, and Aβ plaque and p‐tau in brains were assessed 3 months later. Behavioral studies such as Y‐maze, Morris water maze, and novel‐object‐recognition were conducted to exam the effect of TMEM176B overexpression in alleviation of cognition decline. Result In human AD brains, Tmem176B expression was increased in moderate AD (Braak III‐IV) was decreased in severe AD (Braak V‐VI). TMEM176B was upregulated by acute Aβ treatment in primary rat astrocytes, and was gradually downregulated concomitantly with impairment of Aβ phagocytosis activity by chronic exposure to Aβ. The TMEM176B agonistic compound augmented phagosome maturation and phagosomal acidification, which led to increased Aβ phagocytosis and lysosomal degradation. Studies confirmed that intracerebroventrical administration of AAV carrying TMEM176B in AD mice results in enhanced glial phagocytosis followed by lowered Aβ burden in brain. Moreover, overexpression of TMEM176B by AAV injection significantly improved cognition impairment of AD mice. Conclusion Data from these studies suggest that TMEM176B plays a direct and critical role in phagolysosmal function of glial cells and AD pathogenesis and highlight this ion channel as a potential therapeutic target for treating AD.