Activity-induced Ca2+ signaling in perisynaptic Schwann cells of the early postnatal mouse is mediated by P2Y1 receptors and regulates muscle fatigue

Abstract

Perisynaptic glial cells respond to neural activity by increasing cytosolic calcium, but the significance of this pathway is unclear. Terminal/perisynaptic Schwann cells (TPSCs) are a perisynaptic glial cell at the neuromuscular junction that respond to nerve-derived substances such as acetylcholine and purines. Here, we provide genetic evidence that activity-induced calcium accumulation in neonatal TPSCs is mediated exclusively by one subtype of metabotropic purinergic receptor. In P2ry1 mutant mice lacking these responses, postsynaptic, rather than presynaptic, function was altered in response to nerve stimulation. This impairment was correlated with a greater susceptibility to activity-induced muscle fatigue. Interestingly, fatigue in P2ry1 mutants was more greatly exacerbated by exposure to high potassium than in control mice. High potassium itself increased cytosolic levels of calcium in TPSCs, a response which was also reduced P2ry1 mutants. These results suggest that activity-induced calcium responses in TPSCs regulate postsynaptic function and muscle fatigue by regulating perisynaptic potassium.

Purinergic-Dependent Glial Regulation of Synaptic Plasticity of Competing Terminals and Synapse Elimination at the Neuromuscular Junction

“…This blockade was reversible because Ca 2+ elevations were induced after a 20-min washout of the drug (300.20% ± 12.00% DF/F0, n = 20 PSCs; paired t test, p < 0.0001). This is consistent with recent work showing that purine-induced PSC Ca 2+ responses are mediated exclusively by P2Y1Rs (Heredia et al, 2018) and further confirms that ATP-dependent activation of PSCs is mediated by P2Y1Rs.…”

“…These results using single-cell electroporation are similar to those using bulk loading of the Ca 2+ indicator in PSCs (Darabid et al, 2013). Moreover, PSCs also responded to the local application of ATP (5 mM; Figure 1C; 131.50% ± 48.19% DF/F0; N = 4), which is the main neurotransmitter activating PSCs at developing NMJs (Darabid et al, 2013;Heredia et al, 2018) and is commonly used to assess PSC excitability and health (Arbour et al, 2015;Darabid et al, 2013;Rochon et al, 2001). Altogether, these results confirm that PSCs at a dually innervated NMJ decode synaptic competition and that PSCs can be targeted specifically by single-cell electroporation without undesired effects.…”

“…We next investigated the mechanisms by which PSCs differentially regulate competing inputs. During synaptic competition, PSC Ca 2+ activity is mediated by P2YRs activated by ATP (Darabid et al, 2013;Heredia et al, 2018). Interestingly, although their presence on other synaptic elements cannot be ruled out, P2Y1Rs are located on PSCs during synaptic competition, clustered near presynaptic release sites (Darabid et al, 2013).…”

“…This time window allows analysis of synapse elimination progression (Kopp et al, 2000;Personius and Balice-Gordon, 2001;Personius et al, 2007), including the period of differential synaptic plasticity of terminals (P7-P8). Unlike constitutive knockout (KO) of P2Y1Rs (Heredia et al, 2018), the ages we targeted allow fetal and early post-natal maturation of NMJs (<P4) to proceed normally and limit the recruitment of compensatory mechanisms. The state of innervation (a correlate of the progression of synapse elimination) was determined by the number of mono-and polyinnervated NMJs at the soleus muscle.…”

“…Interestingly, we recently showed that, during NMJ development, persiynaptic schwann cells (PSCs) decode the synaptic activity of competing inputs, via purinergic type 2Y receptors, based on differential synaptically induced intracellular Ca 2+ elevations (Darabid et al, 2013). Furthermore, in purinergic type 2Y1 receptor (P2Y1R) knockout mice, synaptically induced Ca 2+ elevations in PSCs are obliterated (Heredia et al, 2018). PSCs' ability to decode synaptic activity could endow them with the capacity to differentially regulate the synaptic strength of competing terminals and, thus, influence the outcome of synaptic competition and elimination.…”