INTRODUCTION
Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative
disease that targets both upper and lower motor neurons within the brain
and spinal cord. Tragically, ALS is characterized by a brief survival
span of 2-3 years, with only 10-20% of patients surpassing a decade of
life post-diagnosis. Familial cases, attributable to genetic mutations,
account for 5-10% of all ALS cases, with the rest classified as
sporadic . Despite intense ongoing research, current medications such as
Riluzole, Edaravone, Relyvrio, and Qalsody provide only a modest delay
in disease progression. The pathogenesis of ALS is a complex interplay
of multiple processes occurring within motor neurons (MNs), encompassing
amongst other proposed mechanism: excitotoxicity, endoplasmic reticulum
(ER) stress, mitochondrial dysfunction, oxidative stress, RNA processing
aberrations, protein misfolding, endosomal trafficking disruptions,
impaired axonal transport or neuroinflammation . Computational models
have underscored the significance of disturbances in calcium
(Ca2+) homeostasis and energy imbalances as pivotal
factors predicting neuronal dysfunction and degeneration in ALS .
One distinguishing feature in early ALS-affected MNs is the excessive
influx of Ca2+ ions due to high-frequency rhythmic
activity and an increased expression of Ca2+-permeable
AMPA receptors . These MNs exhibit low expression of
Ca2+ buffering proteins like parvalbumin and calbindin
. Overexpression of these proteins has been shown to confer resistance
to ALS-induced toxicity in MNs . Conversely, MNs that exhibit resistance
to ALS degeneration, such as those of oculomotor and Onuf’s nuclei,
possess higher levels of Ca2+ buffering proteins .
Notably, ALS-associated mutations, including those in VAPB ,SIGMAR1 and SOD1 can potentiate Ca2+deregulation and heighten vulnerability to the effects of
Ca2+ influx . These findings emphasize the inherent
susceptibility of MNs to intracellular Ca2+ overload
as a significant risk factor for degeneration .
Mitochondria play a pivotal role in regulating intracellular
Ca2+ levels through the mitochondrial uniporter,
particularly crucial in MNs with low intrinsic cytosolic
Ca2+ buffering capacity. In these vulnerable MNs,
mitochondria are responsible for absorbing over 50% of intracellular
Ca2+ increases, setting them apart from other cell
types. Consequently, the pronounced demand placed on specialized
Ca2+ storage organelles makes MNs even more
susceptible to Ca2+ imbalances , especially in ALS
where mitochondria are frequently damaged . Indeed, impaired
mitochondrial Ca2+ buffering in MNs derived from
patient-induced pluripotent stem cells carrying mutations inTARDBP or C9orf72 has been reported .
Apart from excessive Ca2+ influx and diminished
Ca2+ buffering capacity, augmented
Ca2+ leakage from ER stores in MNs can further
contribute to cytosolic Ca2+ overload. Ryanodine
receptors (RyR) are tetrameric channels that play a crucial role in
mediating Ca2+-induced Ca2+ release
from the ER, play a crucial role in this process . RyR channels are
activated by Ca2+ and can also be triggered by the
oxidation of redox-sensing thiols by reactive oxygen species (ROS),
creating a positive feedback loop exacerbating pathological cytoplasmic
Ca2+ overload . The endogenous ligand of RyR, FKBP12
(calstabin), normally stabilizes RyR, preventing Ca2+leakage from the ER. Reduced FKBP12 levels in MNs of ALS patients
underscore the importance of maintaining equilibrium between FKBP12 and
RyR in neurodegeneration .
Overall, this cumulative evidence suggests the prospect of RyRs as a
potential therapeutic targets for ameliorating intracellular
Ca2+ dysregulation and forestalling
Ca2+-induced neurodegeneration within susceptible
neurons and neuromuscular units in ALS. In this context, we introduce a
novel class of triazole molecules, empirically validated as FKBP12
ligands to facilitate FKBP12-RyR binding. This binding capability serves
to stabilize the Ca2+ flux mediated by RyR, as
demonstrated in our previous works . In this study, we introduce MP
compounds, novel FKBP12 ligands that exhibit cytosolic calcium
modulating activity, with the potential to be used for the treatment of
ALS. This proposal is based on the encouraging results observed in
transgenic SOD1G93A mice, a mouse model that
recapitulates the key clinical, electrophysiological, and
histopathological features of the disease. .