Abstract
Aminoglycoside antibiotics remain essential for treatment of severe Gram-negativebacterial infections, yet their clinical use is limited by the risk of irreversible sensorineural
hearing loss. Many signaling pathways change during ototoxic injury, but transcriptional
change alone does not establish whether a pathway is protective, maladaptive, or merely
reactive in the intact mammalian cochlea. This dissertation tests the hypothesis that
Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling, and
particularly JAK2-dependent signaling, contributes to cochlear resilience during
aminoglycoside ototoxic stress.
To nominate candidate pathways, early gentamicin-responsive hair-cell
transcriptomic data were integrated with LINCS/L1000 perturbational connectivity
mapping. This analysis identified JAK/STAT signaling as a biologically plausible and
clinically relevant pathway for experimental interrogation. In vivo testing then showed that
the biological meaning of this nomination could not be inferred from the screen alone. In
adult mouse models, systemic dual JAK1/2 inhibition with momelotinib worsened hearing
loss and cochlear damage in an inflammatory kanamycin paradigm. Subsequent kinase
specific pharmacologic studies refined this finding: systemic JAK1-biased inhibition with
upadacitinib or tofacitinib did not produce a statistically significant sensitization phenotype
under the conditions tested, whereas inhibitors with substantial JAK2 activity, including
fedratinib and ruxolitinib, consistently increased cochlear vulnerability to kanamycin.
These effects included worsened auditory brainstem response thresholds, reduced
suprathreshold neural output, impaired outer hair cell-dependent cochlear amplification,
and expanded physiologic injury.
To localize the effect genetically, Jak2 was conditionally deleted in Pax2-lineage
otic tissues. Pax2-Cre;Jak2fl/fl mice showed little baseline auditory impairment, but they
were markedly more susceptible to chronic kanamycin exposure. Following injury, these
mice developed exaggerated auditory threshold shifts, greater DPOAE dysfunction,
reduced suprathreshold response amplitudes, prolonged response latencies, and
evidence of altered central gain. Whole-cochlea proteomic analyses provided
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mechanistic support for these functional findings by implicating disruption of
gp130/IL6ST-associated signaling, GH-JAK2-IGF-linked trophic pathways, FGF2
signaling and structural maintenance programs. These data support a model in which
JAK2-dependent signaling maintains a protective trophic and reparative reserve in the
stressed cochlea.
A complementary developmental gain-of-function study demonstrated that chronic
Pax2-lineage activation of JAK2 disrupts auditory maturation, producing broad-spectrum
hearing loss, cochlear amplifier dysfunction, abnormal early brainstem transmission, and
possible changes in neurite and synaptic architecture at baseline. However, because the
gain-of-function cohort was assessed at P28 for auditory physiology and at approximately
P30 for cochlear histology, without later longitudinal follow-up, the current data cannot
determine whether the phenotype represents delayed cochlear maturation that might
partially normalize or a permanent developmental defect. Together, these studies indicate
that JAK2 signaling is context dependent: reduced JAK2 activity sensitizes the mature
cochlea to aminoglycoside injury, whereas chronic developmental hyperactivation
perturbs auditory circuit refinement.Together, these studies indicate that JAK2 signaling
is context dependent: reduced JAK2 activity sensitizes the mature cochlea to
aminoglycoside injury, whereas chronic developmental hyperactivation perturbs auditory
circuit refinement. Overall, this dissertation identifies JAK2-dependent signaling as a
major determinant of cochlear resilience during aminoglycoside ototoxic stress and raises
the translational possibility that JAK2-active inhibitors may increase ototoxic risk in
susceptible clinical settings.