Being a large multidomain protein, LRRK2 has several
confirmed
pathological mutant variants for PD, and the incidence of these variants
shows ethnicity biases. I1371V, a mutation in the GTPase domain, has
been reported in East-Asian populations, but there are no studies
reported on dopaminergic (DA) neurons differentiated from this variant.
The aim here was to assess the yield, function, and α-synuclein
pathology of DA neurons differentiated from LRRK2 I1371V iPSCs. FACS
analysis of neural progenitors (NPs) showed a comparable immunopositive
population of cells for neural and glial progenitor markers nestin
and S100β; however, NPs from I1371V iPSCs showed lower clonogenic
and proliferative capacities than healthy control NPs as determined
by the neurosphere assay and Ki67 expression. Floor plate cells obtained
from I1371V NPs primed with FGF8 showed distinctly lower immunopositivity
for FOXA2 and CLIC5 than healthy control FPCs and similar DOC2B expression.
On SHH addition, a similar mature neuronal population was obtained
from both groups; however, the yield of TH-immunopositive cells was
significantly lower in I1371V, with lower expression of mature DA
neuronal markers En1, Nurr1, and DAT. Vesicular dopamine release and
intracellular Ca2+ response with KCl stimulation were lower
in I1371V DA neurons, along with a significantly reduced expression
of resting vesicle marker VMAT2. A concurrently lower expression of
PSD95/Syn-I immunopositive puncta was observed in I1371V differentiated
cells. Further, higher phosphorylation of α-synuclein and aggregation
of oligomeric α-synuclein in I1371V DA neurons were observed.
Our data demonstrated conclusively for the first time that mutations
in the I1371V allele of LRRK2 showed developmental deficit from the
FPC stage and generated a lower yield/number of TH-immunopositive
neurons with impairment in their function and synapse density along
with increased α-synuclein pathology.