Accelerated cystogenesis by dietary protein load is dependent on, but not initiated by, kidney macrophages
Background: Disease severity of autosomal dominant polycystic kidney disease  (ADPKD) is influenced by diet. Dietary protein, a recognized cyst-accelerating factor, is  catabolized into amino acids (AA) and delivered to the kidney leading to renal  hypertrophy. Injury-induced hypertrophic signaling in ADPKD results in increased  macrophage (M?) activation and inflammation followed by cyst growth. We hypothesize  that the cystogenesis-prompting effects of HP diet are caused by increased delivery of  specific AA to the kidney, ultimately stimulating M?s to promote cyst progression. Methods: Pkd1 flox/flox mice with and without Cre (CAGG-ER) were given tamoxifen to  induce global gene deletion (Pkd1KO). Pkd1KO mice were fed either a low (LP; 6%),  normal (NP; 18%), or high (HP; 60%) diet for 1 week (early) or 6 weeks (chronic). Mice  were then euthanized and tissues were used for histology, immunofluorescence and  various biochemical assays. One week fed kidney tissue was cell sorted to isolate  tubular epithelial cells for RNA sequencing. Results: Chronic dietary protein load in Pkd1KO mice increased kidney weight, number  of kidney infiltrating and resident M?s, chemokines, cytokines and cystic index  compared to LP diet fed mice. Accelerated cyst growth induced by chronic HP were  attenuated by liposomal clodronate-mediated M? depletion. Early HP diet fed Pkd1KO  mice had larger cystic kidneys compared to NP or LP fed counterparts, but without  increases in the number of kidney M?s, cytokines, or markers of tubular injury. RNA  sequencing of tubular epithelial cells in HP compared to NP or LP diet group revealed  increased expression of sodium-glutamine transporter Snat3, chloride channel Clcnka,  and gluconeogenesis marker Pepck1, accompanied by increased excretion of urinary  ammonia, a byproduct of glutamine. Conclusion: Chronic dietary protein load-induced renal hypertrophy and accelerated  cyst growth in Pkd1KO mice is dependent on both infiltrating and resident M?  recruitment and subsequent inflammatory response. Early cyst expansion by HP diet,  however, is relient on increased delivery of glutamine to kidney epithelial cells, driving  downstream metabolic changes prior to inflammatory provocation. Overall design: Kidneys from Pkd1KO mice fed low, normal, and high protein diets (2.8 g/day) for 1 week were collected for flow sorting of the epithelial cell population.