MRPS9 (mitochondrial ribosomal protein S9) is a structural component of the mitochondrial small ribosomal subunit essential for mitochondrial translation 1. As a nuclear-encoded protein, MRPS9 is critical for synthesizing the 13 oxidative phosphorylation subunits encoded by mitochondrial DNA 1. The protein functions within the 82-protein mitoribosomal complex composed of 12S rRNA, 16S rRNA, and associated proteins 2. Mechanistically, MRPS9 regulates neuronal survival through the PI3K/Akt/mTOR signaling pathway 3. MRPS9 overexpression activates this pathway, inhibiting neuronal apoptosis and promoting cell viability under ischemic stress conditions 3. The protein interacts with other mitoribosomal components; perturbation of related mitoribosomal proteins (like DAP3/MRPS29) reduces MRPS9 protein levels, indicating coordinated assembly of the small subunit 1. Clinically, MRPS9 dysregulation is implicated in ischemic stroke (IS) and end-stage renal disease (ESRD) comorbidity 4. Bioinformatic analyses identified MRPS9 as a hub gene in IS-related epigenetic networks 5, with significant downregulation observed in comorbid IS-ESRD patients 4. The protein also appears relevant to cancer prognosis, as MRPS9-AS1 (an antisense lncRNA) associates with prognostic signatures in renal cell carcinoma and colon cancer 6 7. These findings highlight MRPS9's dual role in mitochondrial bioenergetics and disease pathogenesis.