Abstract Body (Do not enter title and authors here): Introduction: Chronic kidney disease (CKD) is a significant healthcare challenge globally and renal proximal tubules (PT) are key targets of injury. Others have shown that patients with CKD have a dysregulated cell cycle in PT, but it remains unclear whether cell cycle progression in CKD is adaptive or maladaptive. Our recent findings indicate that inhibiting cyclin-dependent kinases 4/6 (CDK4/6) is protective in CKD. However, the underlying mechanisms remain incompletely understood.

Research questions and aims: Cell cycle progression is linked to metabolism, and we aim to investigate how CDK4/6 inhibition can alter metabolism. Mitochondrial function is closely intertwined with metabolism, and chronic kidney injury is associated with both impaired mitochondrial function and decreased oxidative metabolism. However, mitophagy, the clearance of dysfunctional mitochondria, protects against CKD progression. This raises the question of how CDK4/6 inhibition affects metabolism, mitochondrial function and mitophagy.

Methods: To define how cell cycle alters metabolism, we measured respirometry using a Seahorse bioflux analyzer on primary PT treated with palbociclib, a CDK4/6 inhibitor. Additionally, we injured mice with uninephrectomy/angiotensin II (UniNx/AngII) +/- palbociclib. To measure glucose oxidation, we incubated injured kidney tissues with ¹⁴[C]-pyruvate and measured the production of ¹⁴CO₂. We analyzed mitochondrial structure in injured kidneys +/- palbociclib using structure illuminated microscopy (SIM). To assess the effect of CDK4/6 inhibition on mitophagy, we used a reporter mouse model “Mito-QC” injured by UniNx/AngII. Mito-QC mice have tandem mCherry-GFP tag fused to the mitochondrial outer membrane protein, but GFP is pH sensitive and is quenched during mitophagy.

Results: Our data indicate that blocking CDK4/6 with palbociclib enhances mitochondrial oxygen consumption in primary PT. Additionally, palbociclib increases glucose/pyruvate oxidation in injured kidneys. Palbociclib preserves mitochondrial connectivity in response to UniNx/AngII-induced kidney injury, as detected by SIM. Moreover, palbociclib-treated mice had increased mitophagy following kidney injury.

Conclusion: Our study shows that CKD4/6 inhibition increases oxidative metabolism and improves mitochondrial function. These effects may be mediating some of the protective effects of palbociclib in chronic renal injury.