Calcium signalling in glial cells

Role of Microglia and Astrocytes in Alzheimer’s Disease: From Neuroinflammation to Ca2+ Homeostasis Dysregulation

Alzheimer’s disease (AD) is the most common form of dementia worldwide, with a complex, poorly understood pathogenesis. Cerebral atrophy, amyloid-β (Aβ) plaques, and neurofibrillary tangles represent the main pathological hallmarks of the AD brain. Recently, neuroinflammation has been recognized as a prominent feature of the AD brain and substantial evidence suggests that the inflammatory response modulates disease progression. Additionally, dysregulation of calcium (Ca2+) homeostasis represents another early factor involved in the AD pathogenesis, as intracellular Ca2+ concentration is essential to ensure proper cellular and neuronal functions. Although growing evidence supports the involvement of Ca2+ in the mechanisms of neurodegeneration-related inflammatory processes, scant data are available on its contribution in microglia and astrocytes functioning, both in health and throughout the AD continuum. Nevertheless, AD-related aberrant Ca2+ signalling in astrocytes and microglia is crucially involved in the mechanisms underpinning neuroinflammatory processes that, in turn, impact neuronal Ca2+ homeostasis and brain function. In this light, we attempted to provide an overview of the current understanding of the interactions between the glia cells-mediated inflammatory responses and the molecular mechanisms involved in Ca2+ homeostasis dysregulation in AD.

Spatio-temporal expression analysis of the calcium-binding protein calumenin in the rodent brain

Calumenin is a Ca²⁺-binding protein that belongs to the CREC superfamily. It contains six EF-hand domains that exhibit a low affinity for Ca²⁺ as well as an endoplasmic reticulum retention signal. Calumenin exhibits a broad and relatively high expression in various brain regions during development as demonstrated by in situ hybridization. Signal intensity of calumenin is highest during the early development and then declines over time to reach a relatively low expression in adult animals. Immunohistochemistry indicates that at the P0 stage, calumenin expression is most abundant in migrating neurons in the zones around the lateral ventricle. In the brain of adult animals, it is expressed in various glial and neuronal cell types, including immature neurons in subgranular zone of hippocampal dentate gyrus. At the subcellular level, calumenin is identified in punctuate and diffuse distribution mostly in somatic regions where it co-localizes with endoplasmic reticulum (ER) and partially Golgi apparatus. Upon subcellular fractionation, calumenin is enriched in fractions containing membranes and is only weakly present in soluble fractions. This study points to a possible important role of calumenin in migration and differentiation of neurons, and/or in Ca²⁺ signaling between glial cells and neurons.