Hypothesis: Chronic low‑level UVA exposure accelerates corneal stromal aging by inducing keratocyte senescence that up‑regulates lysyl oxidase–like (LOXL) enzymes, leading to pathological non‑enzymatic collagen cross‑linkage and impaired fibrillogenesis. Simultaneous clearance of senescent keratocytes and pharmacological inhibition of LOXL activity will reverse both cellular and extracellular abnormalities, restoring stromal transparency and biomechanical normoxia.

Mechanistic Rationale: UVA exposure down‑regulates collagen and proteoglycan gene expression in keratocytes [5] and promotes a senescence‑associated secretory phenotype that includes LOXL2/LOXL4 [2]. These enzymes catalyze lysine‑derived cross‑links that exceed the effects of advanced glycation end products, producing stromal stiffening, increased fibril roughness, and light scattering [3][4]. Senolytics such as dasatinib+quercetin eliminate senescent fibroblasts and improve abnormal ECM remodeling in skin [6], suggesting that clearing senescent keratocytes will reduce the SASP‑driven LOXL surge. However, removing the source does not instantly degrade existing pathological cross‑links; direct LOXL inhibition is required to prevent further aberrant linkage and allow matrix remodeling. The combination thus addresses both the cellular trigger and the enzymatic effector.

Predictions: 1) UVA‑exposed mice will show increased p16^INK4a+, SA‑β‑gal+ keratocytes, elevated LOXL2/LOXL4 mRNA, and higher hydroxylysyl pyridinoline cross‑links. 2) Senolytic treatment alone will lower senescence markers but will not normalize cross‑link levels. 3) LOXL inhibition alone will decrease cross‑linking without rescuing keratocyte density. 4) Combined senolytic + LOXL inhibitor will restore keratocyte density, collagen organization (quantified by second‑harmonic generation imaging), corneal haze score, and tensile strength to sham levels.

Experimental Design: Use 8‑week‑old C57BL/6 mice, expose the right eye to 0.5 J/cm² UVA three times weekly for 12 weeks; left eye receives sham. Four treatment arms (n=10 per arm): vehicle, dasatinib+quercetin (D+Q) 5 mg/kg i.p. twice weekly, LOXL2/LOXL4 inhibitor PXS‑5505 30 mg/kg oral daily, and D+Q + PXS‑5505. At week 13 assess: flow cytometry for keratocyte viability, immunofluorescence for p16 and SA‑β‑gal, qPCR for LOXL2/LOXL4, HPLC for hydroxylysyl pyridinoline, slit‑lamp haze grading, SHG imaging for fibril spacing and alignment, and corneal tensile strength testing. Analyze with two‑way ANOVA and Tukey post‑hoc.

Potential Outcomes: If the hypothesis is correct, only the combined therapy group will show significant reductions in senescence markers, pathological cross‑link density, and haze, accompanied by stromal thickness and tensile strength matching sham eyes. Failure of senolytics to lower cross‑links would falsify the mechanistic link between keratocyte senescence and LOXL‑driven ECM alteration; rescue of keratocyte density by LOXL inhibition alone would indicate that cross‑links feed back to impair cell survival, requiring model revision.

Implications: This work reframes UVA‑induced corneal aging as a dual hit of cellular senescence and enzymatically mediated cross‑linking, supporting a combinatorial senolytic‑LOXL strategy that goes beyond current corneal cross‑linking approaches which only increase stromal rigidity. Success would provide a translatable path to preserve transparency in aging populations and UV‑exposed individuals.

References: [1] https://pubmed.ncbi.nlm.nih.gov/41850336/?fc=20240423212545&ff=20260319191530&v=2.19.0.post6+133c1fe [2] https://pubmed.ncbi.nlm.nih.gov/11080534/ [3] https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2019.00066/full [4] https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0292791 [5] https://onlinelibrary.wiley.com/doi/10.1111/acel.12324 [6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10284692/