Zarate, S. M. | bioRxiv Science

bioRxiv2021

Aging reduces calreticulin expression and alters spontaneous calcium signals in astrocytic endfeet of the mouse dorsolateral striatum

Aging-related impairment of the blood brain barrier (BBB) and neurovascular unit (NVU) increases risk for neurodegeneration. Among the various cells participating in BBB and NVU function, spontaneous Ca2+ signals in astrocytic endfeet are crucial for maintaining BBB and NVU integrity. To assess if aging is associated with changes in spontaneous Ca2+ signals within astrocytic endfeet of the dorsolateral striatum (DLS), we expressed a genetically encoded Ca2+ indicator, Lck-GCaMP6f in DLS astrocytes of young (3-4 month) and aging (20-24 month) mice. Compared to young mice, endfeet in the DLS of aging mice demonstrated a decrease in calreticulin (CALR) expression, and dramatic alterations in the dynamics of endfoot membrane-associated and mitochondrial Ca2+ signals. While young mice required both extracellular and endoplasmic reticulum (ER) Ca2+ sources for generating endfoot Ca2+ signals, aging mice showed exclusive dependence on ER Ca2+. These data suggest that aging is associated with significant changes in Ca2+ buffers and Ca2+ signals within astrocytic endfeet, which has important implications for understanding mechanisms involved in aging-related impairment of the BBB and NVU. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=118 SRC="FIGDIR/small/461710v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@1d61571org.highwire.dtl.DTLVardef@19e2f9org.highwire.dtl.DTLVardef@18455cborg.highwire.dtl.DTLVardef@11ca928_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIAging mice show reduced calreticulin expression in astrocytic endfeet C_LIO_LIAging astrocytic endfeet show dramatic changes in spontaneous Ca2+ activity C_LIO_LICa2+ signals in aging endfeet depend exclusively on endoplasmic reticulum Ca2+ C_LI

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bioRxiv2021

Extracellular S100B alters spontaneous Ca2+ fluxes in dopaminergic neurons via L-type voltage gated calcium channels: Implications for Parkinson's disease

Parkinsons disease (PD) is associated with an abnormal increase in S100B within the midbrain and cerebrospinal fluid. In addition, overexpression of S100B in mice accelerates the loss of substantia nigra pars compacta (SNc) dopaminergic (DA) neurons, suggesting a role for this protein in PD pathogenesis. We found that in the mouse SNc, S100B labeled astrocytic processes completely envelop the somata of tyrosine hydroxylase (TH) positive DA neurons. Based on this finding, we rationalized that abnormal increases in extracellularly secreted S100B by astrocytic processes in the SNc could alter DA neuron activity, thereby causing dysregulated midbrain function. To test this hypothesis, we measured the effect of bath perfused S100B peptide on the frequency and amplitude of spontaneous calcium fluxes in identified TH+ and TH- midbrain neurons from 3-week old mouse primary midbrain cultures. Acute exposure to 50 pM S100B caused a 2-fold increase in calcium flux frequency only in TH+ DA neurons. The L-type voltage gated calcium channel (VGCC) inhibitor, diltiazem eliminated S100B-mediated increases in DA neuron calcium flux frequency, while the T-type specific VGCC blocker mibefradil failed to inhibit the stimulatory effect of S100B. Chronic exposure to S100B caused a 3-fold reduction in calcium flux frequencies of TH+ neurons and also reduced calcium flux amplitudes in TH- neurons by [~]4-fold. Together, our results suggest that exposure to S100B pathologically alters spontaneous calcium activity in midbrain neurons via an extracellular mechanism involving L-type VGCCs expressed in DA neurons. These findings are relevant to understanding mechanisms underlying DA neuron loss during PD. Table of Contents Image O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=160 SRC="FIGDIR/small/432751v1_ufig1.gif" ALT="Figure 1"> View larger version (62K): org.highwire.dtl.DTLVardef@7d3fd3org.highwire.dtl.DTLVardef@e96b3corg.highwire.dtl.DTLVardef@7f6d21org.highwire.dtl.DTLVardef@1d5bde4_HPS_FORMAT_FIGEXP M_FIG C_FIG Main PointsO_LIExtracellular S100B increases Ca2+ fluxes in dopaminergic neurons C_LIO_LIL-type VGCCs in dopaminergic neurons are required for S100B-mediated increases in Ca2+ fluxes C_LIO_LIChronic S100B alters Ca2+ fluxes in dopaminergic and non-dopaminergic neurons C_LI

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