Symptom Duration-Dependent Protein Abundance Changes in Symptomatic and Asymptomatic Tendons in Early Stage Unilateral Patellar Tendinopathy

Tendinopathy
is a painful overuse disorder marked by a progressive
functional decline. Although chronic disease mechanisms have been
described, early molecular changes remain poorly defined. Here, we
performed temporal proteomic profiling of human patellar tendon biopsies
across one, two, and three months of symptom duration and evaluated
proteome differences between symptomatic and nonsymptomatic contralateral
tendons. Biopsies were collected from participants with unilateral
patellar tendinopathy and symptoms lasting three months or less for
analysis by data-independent acquisition liquid chromatography–mass
spectrometry. Peptide- and protein-level abundances were quantified
as part of a bottom-up proteomics workflow and assessed using two-way
ANOVA with factors of symptom status and symptom duration. Symptom
duration had a significant main effect: 12 proteins and 14 peptides
changed significantly over time, with most peptides corresponding
to the altered proteins. However, there was no interaction between
the symptom status and symptom duration, no sex differences, and no
detectable proteomic difference between symptomatic and contralateral
tendons. These findings indicate that protein-level changes are detectable
within the first three months of tendinopathy, and similar proteomic
changes were also observed in contralateral tendons. Together, these
observations suggest that early phase patellar tendinopathy is associated
with time-dependent proteomic changes that are not confined to the
symptomatic tendon.