Abstract
Background: Cladribine (CdA), an oral prodrug approved for the treatment
of relapsing multiple sclerosis, selectively depletes lymphocytes. CdA
passes the blood-brain barrier suggesting a potential effect on CNS
resident cells. Objective: We examined, if CdA modifies the phenotype
and function of naïve and activated primary mouse microglia, when
applied in different concentrations including 0.1-1 µM that putatively
overlaps human CSF concentrations. Methods: Primary microglia cultures
without stimulation or in the presence of proinflammatory
lipopolysaccharide (LPS) or anti-inflammatory IL-4 were co-treated with
different concentrations of CdA for 24 hours. Viability was assessed by
MTT assay. Phagocytotic ability and morphology were examined by flow
cytometry, and random migration by IncuCyte Zoom and TrackMate. Change
in gene expression was examined by qPCR, and protein secretion by Meso
Scale Discovery. Results: LPS and IL-4 upregulated deoxycytidine kinase
(DCK) expression. Only activated microglia were affected by CdA, and
this was unrelated to viability. CdA 0.1-1 µM significantly reduced
granularity, phagocytotic ability and random migration of activated
microglia. CdA 10 µM increased the IL-4-induced gene expression of Arg1
and LPS-induced expression of IL-1beta, TNF, iNOS, and Arg1, but protein
secretion remained unaffected. CdA 10 µM potentiated the increased
expression of anti-inflammatory TNFR2 but not TNFR1 induced by LPS.
Conclusion: Microglia acquire a less activated phenotype when treated
with 0.1–1 µM CdA that putatively overlaps human CSF concentrations.
This may be related to the upregulated gene expression of DCK upon
activation and suggests a potential alternative mechanism of CdA with
direct effect on CNS resident cells.