Aging is strongly linked to mitochondrial dysfunction, which disrupts energy metabolism and tissue homeostasis. The salivary gland is an energy-dependent organ, and mitochondrial decline contributes to age-related atrophy and impaired secretion. In this study, we investigated whether spermidine can restore mitochondrial function in aging salivary glands. In aging accelerated klotho deficient mouse, spermidine supplementation improved glandular histology, restoring acinar organization and reducing atrophy. Transcriptomic profiling revealed that spermidine induced extensive transcriptional reprogramming, characterized by the upregulation of mitochondrial metabolic pathways and suppression of inflammatory signaling. qRT-PCR and Western blot analyses confirmed increased expression of PPARγ mediated mitochondrial membrane potential such as PGC-1α, NRF1/2, and OXPHOS complex subunits. Furthermore, spermidine elevated mitochondria oxygen consumption rate, including basal respiration, ATP production, maximal respiration, and spare respiratory capacity. These results demonstrated that spermidine improves mitochondria respiratory capacity through activation of the PPAR–PGC-1α–NRF regulatory axis and may serve as a potential therapeutic strategy for restoring mitochondrial homeostasis and preserving salivary gland function during aging.

Ⅰ. INTRODUCTION
Ⅱ. MATERIALS and METHODS
    1. Animals and treatment
    2. Histological analysis
    3. RNA seq analysis
    4. Cell culture and treatment
    5. Western blot analysis
    6. Quantitative reverse transcription polymerasechain reaction (qRT–PCR) analysis
    7. Mitochondrial membrane potential assay (JC-1)
    8. Oxygen consumption rate assay
    9. Statistical analysis
Ⅲ. RESULTS
    1. Spermidine preserves salivary gland histologicalproperty in kl-/- mice
    2. RNA-seq of salivary gland in spermidine treatedkl-/- mice
    3. Spermidine upregulates genes involved in lipidmetabolism and mitochondrial β-oxidation
    4. Spermidine activates mitochondria regulatorysignaling and increases expression of OXPHOScomplexes
    5. Spermidine induces mitochondrial membranepotential and ATP production in kl-/- PSGCs
    6. Spermidine regulates OXPHOS pathways throughPPAR/PGC-1 signaling
Ⅳ. DISCUSSION
AKNOWLEDGEMENTS
REFERENCES

• 응우옌 유이 푸(조선대학교 치과대학 병리학교실) | Nguyen Duy Phu (Department of Pathology, School of Dentistry, Chosun University)
• 안상건(조선대학교 치과대학 병리학교실) | Sang-Gun Ahn (Department of Pathology, School of Dentistry, Chosun University) Corresponding author