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Although renal macrophages have been shown to contribute to cystic kidney disease in PKD animal models, it remains unclear if there is a specific macrophage subpopulation involved. Here we analyze changes in macrophage populations during renal maturation in association with cystogenesis rates in conditional Pkd2 mutant mice. We demonstrate that CD206+ resident macrophages are minimal in a normal adult kidney but accumulate in cystic areas in adult-induced Pkd2 mutants. Using Cx3cr1 null mice, we reduced macrophage number, including CD206+ macrophages, and show this significantly reduces cyst severity in adult-induced Pkd2 mutant kidneys. We also found that the number of CD206+ resident macrophage-like cells increases in kidneys and in the urine from ADPKD patients relative to the rate of renal functional decline. These data indicate a direct correlation between CD206+ resident macrophages and cyst formation and demonstrate that the CD206+ resident macrophages in urine may serve as a biomarker for renal cystic disease activity in preclinical models and ADPKD patients.

Molecular chaperone Hsp70 plays important roles in the pathology of amyloid diseases by inhibiting aberrant aggregation of proteins. However, the biophysical mechanism of the interaction of Hsp70 with the intrinsically disordered proteins (IDPs) is unclear. Here, we report that Hsp70 inhibits aggregation of islet amyloid polypeptide (IAPP) at substoichiometric concentrations under diverse solution conditions, including in the absence of ATP. The inhibitory effect is strongest if Hsp70 is added in the beginning of aggregation but progressively less if added later, indicating a role for Hsp70 in preventing nucleation of IAPP. However, ensemble measurement of the binding affinity suggests poor interactions between Hsp70 and IAPP. Therefore, we hypothesize that the interaction must involve a rare species (e.g., the oligomeric intermediates of IAPP). Size exclusion chromatography and field flow fractionation are then used to fractionate the constituent species. Multiangle light scattering and fluorescence correlation spectroscopy measurements indicate that the dominant fraction in size exclusion chromatography contains a few nanomolar Hsp70-IAPP complexes amid several μmoles of free Hsp70. Using single-particle two-color coincidence detection measurements, we detected a minor fraction that exhibits fluorescence bursts arising from heterogeneous oligomeric complexes of IAPP and Hsp70. Taken together, our results indicate that Hsp70 interacts poorly with the monomers but strongly with oligomers of IAPP. This is likely a generic feature of the interactions of Hsp70 chaperones with the amyloidogenic IDPs. Whereas high-affinity interactions with the oligomers prevent aberrant aggregation, poor interaction with the monomers averts interference with the physiological functions of the IDPs.

Molecular chaperone Hsp70 plays important roles in the pathology of amyloid diseases by inhibiting aberrant aggregation of proteins. However, mechanism of the interactions of Hsp70 with the amyloidogenic intrinsically disordered proteins (IDPs) is not clear. Here, we use Hsp70 from different organisms to show that it inhibits aggregation of Islet amyloid polypeptide (IAPP) at substoichiometric concentrations even in absence of ATP. The effect is found to be the strongest if Hsp70 is added in the beginning of aggregation but progressively less if added later, indicating role of Hsp70 in preventing primary nucleation possiblyviainteractions with the prefibrillar oligomers of IAPP. Fluorescence Correlation Spectroscopy (FCS) measurements of the solutions containing fluorescently labelled Hsp70 and IAPP exhibit fluorescence bursts suggesting formation of heterogeneous complexes of oligomeric IAPP binding to multiple molecules of Hsp70. Size exclusion chromatography and field flow fractionation are then used to fractionate the smaller complexes. Multiangle light scattering and FCS measurements suggest that these complexes comprise of monomers of Hsp70 and small oligomers of IAPP. However, concentration of the complexes is measured to be a few nanomolar amidst several μmolar of free Hsp70 and IAPP. Hence, our results indicate that Hsp70 interacts poorly with the monomers but strongly with oligomers of IAPP. This is likely a common feature of the interactions between the chaperones and the amyloidogenic IDPs. While strong interactions with the oligomers prevent aberrant aggregation, poor interaction with the monomers avert interference with the functions of the IDPs.