Calcium signaling in human and mouse microglia exhibit differential susceptibility to phytocannabinoids

Neurological disorders affect over 40% of the global population and are driven in part by microglia-mediated neuroinflammation that depends on calcium (Ca²⁺) signaling. Cannabis-derived compounds (CBx) modulate microglial activation and cytokine release, however, the impact of understudied CBx on Ca²⁺ signaling pathways controlling inflammatory responses remains largely unknown.

Here, we systematically examined the effects of over 22 CBx on key microglial Ca²⁺ signaling pathways. Using pharmacological modulators, live-cell Ca²⁺ imaging, immunofluorescence, and cytokine and nitric oxide assays, we characterized store-operated Ca²⁺ entry (SOCE) and purinergic signaling dynamics, inflammatory responses, and CBx effects in human (HMC3) and mouse (BV2) microglia under resting and activated conditions.

We found that microglial SOCE in both mouse and human cell line models were potently inhibited by the same three, minor, acidic CBx - CBGA, CBGVA, CBDVA. In BV2, at least seven CBx (CBD, CBG, CBDVA, CBDA, CBGA, CBDV, CBNM) inhibited LPS-induced proinflammatory secretion of nitric oxide (NO) and TNF-α. Despite the profound SOCE inhibition in HMC3, CBx failed to inhibit downstream proinflammatory cytokine release in TNF-α - or IL-1β-activated cells. We found major differences in Ca²⁺ signaling between the models, including purinergic pathways, where HMC3 cells appear to express a more limited purinome with more subdued signaling responses. Purinergic Ca²⁺ responses to ATP in BV2, especially the delayed phase, was suppressed by at least eight CBx, and most prominently by CBDVA, CBGVA and CBGA. We observed partial, indirect involvement of P2X4, P2 X7, and P2Y13 purinoceptors and propose additional Ca²⁺ signaling targets mediating the anti-inflammatory properties of CBx. Additionally, we documented the pro-inflammatory potential of CBCA and CBNA that is likely facilitated by their ability to mobilize intracellular Ca²⁺ levels in both, human and mouse microglia.

These findings provide a comprehensive qualitative and quantitative assessment of how individual CBx influence main Ca²⁺ signaling pathways in microglia and identify novel anti-inflammatory candidates with therapeutic potential for targeting microglial activation.