Hypothesis

Chronic dysregulation of kinase signaling reshapes the selective autophagy hierarchy, causing mitophagy to be deprioritized despite overall autophagy upregulation, and this shift drives age‑related neuronal loss.

Mechanistic Rationale

Selective autophagy receptors (SARs) such as p62, OPTN and NIX compete for limited LC3 pools. Their affinity is tuned by phosphorylation: CK2 phosphorylates NIX to boost mitophagy, while Hrr25 phosphorylates OPTN to favor ER‑phagy 1 2. In aging neurons, CK2 activity declines whereas stress‑activated kinases (e.g., mTORC1‑S6K) increase, altering the phosphorylation landscape. We propose that the resulting shift in SAR phosphorylation reduces NIX‑LC3 binding relative to p62‑LC3, reorganizing the cargo‑eat‑me hierarchy so that protein aggregates are cleared preferentially while damaged mitochondria persist. This explains why broad autophagy inducers (e.g., rapamycin) often fail to improve mitochondrial health in aged models 3.

Testable Predictions

1. In aged mouse brain, phospho‑NIX levels will be lower and phospho‑p62 higher compared with young controls, correlating with reduced mitophagy flux.
2. Pharmacological restoration of CK2 activity (using a brain‑penetrant CK2 activator) will increase NIX phosphorylation, re‑establish mitophagy priority, and rescue neuronal survival without changing bulk LC3‑II levels.
3. Conversely, inhibiting Hrr25‑like kinases will diminish OPTN phosphorylation, shifting the hierarchy back toward mitochondria and protecting against ER‑stress‑induced apoptosis.

Experimental Design

• Use western blot with phospho‑specific antibodies to quantify p‑NIX (Ser/Thr) and p‑p62 (Ser403) in cortical lysates from 3‑month vs 24‑month mice.
• Measure mitophagy flux with mt‑Keima reporter and aggregate clearance with p62‑GFP puncta.
• Treat aged mice with a CK2 activator (e.g., CX‑4945 low dose) or an Hrr25 inhibitor analog for 4 weeks; assess motor performance (rotarod) and neuronal counts (NeuN+).
• Include controls: vehicle, rapamycin (bulk autophagy inducer), and genetic NIX knock‑down to confirm specificity.
• Statistical analysis: two‑way ANOVA with age and treatment as factors; p<0.05 considered significant.

If CK2 activation restores mitophagy and improves outcomes while bulk autophagy remains unchanged, the hypothesis is supported. Failure to alter the SAR phosphorylation hierarchy or lack of functional rescue would falsify the claim.