The ischemically injured kidney undergoes tubular cell necrosis and apoptosis, accompanied by an interstitial inflammatory cell infiltrate. In this study, we show that iNos-positive proinflammatory (M1) macrophages are recruited into the kidney in the first 48 hours after ischemia/reperfusion injury, whereas arginase 1-and mannose receptor-positive, noninflammatory (M2) macrophages predominate at later time points. Furthermore, depletion of macrophages before ischemia/reperfusion diminishes kidney injury, whereas depletion at 3 to 5 days after injury slows tubular cell proliferation and repair. Infusion of Ifn␥-stimulated, bone marrowderived macrophages into macrophage-depleted mice at the time of kidney reperfusion restored injury to the level seen without macrophage depletion, suggesting that proinflammatory macrophages worsen kidney damage. In contrast, the appearance of macrophages with the M2 phenotype correlated with the proliferative phase of kidney repair. In vitro studies showed that IFN␥-stimulated, proinflammatory macrophages begin to express markers of M2 macrophages when cocultured with renal tubular cells. Moreover, IL-4 -stimulated macrophages with an M2 phenotype, but not IFN␥-stimulated proinflammatory macrophages, promoted renal tubular cell proliferation. Finally, tracking fluorescently labeled, IFN␥-stimulated macrophages that were injected after injury showed that inflammatory macrophages can switch to an M2 phenotype in the kidney at the onset of kidney repair. Taken together, these studies show that macrophages undergo a switch from a proinflammatory to a trophic phenotype that supports the transition from tubule injury to tubule repair.

Autosomal dominant polycystic liver disease results from mutations in PRKCSH or SEC63. The respective gene products, glucosidase IIβ and SEC63p, function in protein translocation and quality control pathways in the endoplasmic reticulum. Here we show that glucosidase IIα and Sec63p are required in mice for adequate expression of a functional complex of the polycystic kidney disease gene products, polycystin-1 and polycystin-2. We find that polycystin-1 is the rate-limiting component of this complex and that there is a dose-response relationship between cystic dilation and levels of functional polycystin-1 following mutation of Prkcsh or Sec63. Reduced expression of polycystin-1 also serves to sensitize the kidney to cyst formation resulting from mutations in Pkhd1, the recessive polycystic kidney disease gene. Finally, we show that proteasome inhibition increases steady-state levels of polycystin-1 in cells lacking glucosidase IIβ and that treatment with a proteasome inhibitor reduces cystic disease in orthologous gene models of human autosomal dominant polycystic liver disease.

Polycystic kidney disease (ADPKD) results from failure of the kidney to properly maintain three-dimensional structure after loss of either polycystin-1 or -2. Mice with kidney selective inactivation of Pkd1 during embryogenesis develop profound renal cystic disease and die from renal failure within 3 weeks of birth. In this model, cysts form exclusively from cells in which Cre recombinase is active, but the apparent pace of cyst expansion varies by segment and cell type. Intercalated cells do not participate in cyst expansion despite the presence of cilia up to at least postnatal day 21. Cystic segments show a persistent increase in proliferation as determined by bromodeoxyuridine (BrdU) incorporation; however, the absolute proliferative index is dependent on the underlying proliferative potential of kidney tubule cells. Components of the extracellular regulated kinase (MAPK/ERK) pathway from Ras through MEK1/2 and ERK1/2 to the effector P90(RSK) are activated in both perinatal Pkd1 and adult Pkd2 ortholgous gene disease models. The pattern of MAPK/ERK activation is focal and does not correlate with the pattern of active proliferation identified by BrdU uptake. The possibility of a causal relationship between ERK1/2 activation and cyst cell proliferation was assessed in vivo in the acute perinatal Pkd1 model of ADPKD using MEK1/2 inhibitor U0126. U0126 treatment had no effect on progression of cyst formation in this model at doses sufficient to reduce phospho-ERK1/2 in cystic kidneys. Cysts in ADPKD exhibit both increased proliferation and activation of MAPK/ERK, but cyst growth is not prevented by inhibition of ERK1/2 activation.

Renal cyst development and expansion in autosomal dominant polycystic kidney disease (ADPKD) involves both fluid secretion and abnormal proliferation of cyst-lining epithelial cells. The chloride channel of the cystic fibrosis transmembrane conductance regulator (CFTR) participates in secretion of cyst fluid, and the mammalian target of rapamycin (mTOR) pathway may drive proliferation of cyst epithelial cells. CFTR and mTOR are both negatively regulated by AMP-activated protein kinase (AMPK). Metformin, a drug in wide clinical use, is a pharmacological activator of AMPK. We find that metformin stimulates AMPK, resulting in inhibition of both CFTR and the mTOR pathways. Metformin induces significant arrest of cystic growth in both in vitro and ex vivo models of renal cystogenesis. In addition, metformin administration produces a significant decrease in the cystic index in two mouse models of ADPKD. Our results suggest a possible role for AMPK activation in slowing renal cystogenesis as well as the potential for therapeutic application of metformin in the context of ADPKD.

Polycystic kidney disease (PKD) can arise from either developmental or postdevelopmental processes. Recessive PKD, caused by mutations in PKHD1, is a developmental defect, whereas dominant PKD, caused by mutations in PKD1 or PKD2, occurs by a cellular recessive mechanism in mature kidneys. Oriented cell division is a feature of planar cell polarity that describes the orientation of the mitotic axes of dividing cells during development with respect to the luminal vector of the elongating nephron. In polycystic mutant mice, the loss of oriented cell division may also contribute to the pathogenesis of PKD. Here, we examined the role of oriented cell division in mouse models based on mutations in Pkd1, Pkd2, and Pkhd1. Precystic tubules after kidney-selective inactivation of either Pkd1 or Pkd2 did not lose oriented division before cystic dilation but lost oriented division after tubular dilation began. In contrast, Pkhd1 del4/del4 mice lost oriented cell division but did not develop kidney cysts. Increased intercalation of cells into the plane of the tubular epithelium maintained the normal tubular morphology in Pkhd1 del4/del4 mice, which had more cells present in transverse tubular profiles. In conclusion, loss of oriented cell division is a feature of Pkhd1 mutation and cyst formation, but it is neither sufficient to produce kidney cysts nor required to initiate cyst formation after mutation in Pkd1 or Pkd2.