Tulp3 Is a Ciliary Trafficking Gene that Regulates Polycystic Kidney Disease

Silva

et al. 2020

Preprint

Background: Primary cilia are sensory organelles that are built and maintained by intraflagellar transport (IFT) multi-protein complexes. Deletion of certain ciliary genes in Autosomal Dominant Polycystic Kidney Disease (ADPKD) mouse models markedly attenuates PKD severity, indicating that a component of cilia dysfunction may have critical therapeutic potential. Method:We have ablated the Ift-A gene, Thm1, globally in juvenile and adult mouse models of ADPKD.Results: Relative to juvenile Pkd2 conditional knock-out mice, deletion of Thm1 together with Pkd2 resulted in a complex phenotype, with reduced kidney weight/body weight (KW/BW) ratios, reduced cortical collecting duct-derived cysts, but increased proximal tubular and glomerular dilations, and similar blood urea nitrogen (BUN) levels. Additionally, primary cilia of cortical collecting duct epithelia were lengthened in Pkd2 conditional knock-out kidneys, as well as in Pkd2;Thm1 double knock-out kidneys. In contrast, Thm1 deletion in adult ADPKD mouse models markedly reduced multiple disease parameters, including KW/BW ratios, collecting duct-and loop of Henle-derived cysts, proximal tubular dilations, and BUN levels. Further, primary cilia lengths of cortical collecting duct epithelia were increased in Pkd1 and Pkd2 conditional knock-out mice, but similar to control in Pkd1;Thm1 and Pkd2;Thm1 double knock-out mice.Conclusions: These data reveal that during kidney development, Thm1 both promotes and inhibits different aspects of ADPKD renal cystogenesis in a tubule-dependent manner; however, during adult kidney homeostasis, Thm1 promotes virtually all features of ADPKD renal cyst growth. These findings suggest that differential factors between tubules and between developing versus mature renal microenvironments influence cilia dysfunction and ADPKD pathobiology.

Section: Discussionmentioning

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Intraflagellar transport-A deficiency attenuates ADPKD in a renal tubular- and maturation-dependent manner

Silva

et al. 2020

Preprint

“…So far, TULP proteins have a well-established role in the selective transport of G-proteincoupled receptors (GPCRs), channels, enzymes, and signaling proteins into cilia (Badgandi et al, 2017;DiTirro et al, 2019;Han et al, 2019;Legué and Liem, 2019;Sun et al, 2012). Intriguingly, a recent study showed that E-Syt3 is specifically expressed in hypothalamic nuclei involved in energy homeostasis and food intake (Zhang et al, 2020), and thus shows a striking overlap with neuronal tubby expression (including the arcuate nucleus) (Kleyn et al, 1996).…”

Section: Biological Function Of Tubby (And Tulp) Localizationmentioning

confidence: 99%

Local PI(4,5)P₂pool dynamics detected by the coincidence biosensor tubbyCT maintain the integrity of ER-PM junctions during PLC signaling

Thallmair

Schultz

Evers

et al. 2020

Preprint

Phosphoinositides (PIs) are important signaling molecules and determinants of membrane identity in the eukaryotic plasma membrane, where they multi-task in divergent signaling pathways. Signaling pleiotropy likely depends on distinct PI pools in the same membrane, although the physical definition of such pools has remained ambiguous. PI(4,5)P2, specifically, is also the precursor for the second messengers in the Gq/PLC pathway, IP3 and DAG, and is broken down by PLCβ during signaling. Endoplasmic reticulum-plasma membrane contact sites (ER-PM junctions) have emerged as central hubs for lipid transport between both membranes, and specifically for PI homeostasis by supplying the PM with phosphatidylinositol.Here we show that the tubby protein, by virtue of its C-terminal tubby-domain, preferentially localizes to ER-PM junctions by binding to both PI(4,5)P2 and the ER-PM tether E-Syt3. Under conditions of vigorous PI(4,5)P2 consumption by PLCβ, additional recruitment of tubby revealed an increase of a local PI(4,5)P2 pool fed by local synthesis through PI kinases. Inhibition of this pool-filling process led to the release of the ER-PM tethers, E-Syts, from the membrane and hence to loss of integrity of the ER-PM contact sites.We conclude that spatiotemporal metabolic channeling of PI synthesis initiated by non-vesicular transport in the ER-PM junctions specifies a local pool of PI(4,5)P2 that is pivotal for the maintenance of homeostatic functions during global depletion of PI(4,5)P2. The findings further suggest that the tubby-like proteins (TULPs), so far known to impact on energy homeostasis and obesity through primary cilia signaling, have an additional function at ER-PM junctions.HIGHLIGHTSThe tubby domain preferentially assembles into ER-PM junctions due to coincidence detection of PI(4,5)P2 and E-Syt3Tubby recruitment reveals an increase of a local pool of PI(4,5)P2 in ER-PM junctions during PLCβ signalingJunctional PI(4,5)P2 dynamics require local synthesis of PI(4,5)P2Local PI(4,5)P2 supply is required for integrity of ER-PM junctions during PLCβ activity.

“…Our finding of Tulp3 in almost all Inpp5e rdg/rdg neural tube cilia raises another 464 possibility. Tulp3 is known to traffic multiple GPCRs into the cilium as well as other molecules 465 known to regulate the Shh pathway, so perhaps Tulp3 is regulating another modulator of the 466 Shh response (Mukhopadhyay et al, 2010, Hwang et al, 2019, Legue and Liem, 2019, Han et 467 al., 2019, Badgandi et al, 2017. Taken together, this would explain the paradoxical increase in 468 Shh signaling in the presence of high Tulp3 and Gpr161 seen in our embryos.…”

mentioning

confidence: 99%

Ciliary phosphatidylinositol phosphatase Inpp5e plays positive and negative regulatory roles in Shh signaling

Constable

Long

Floyd

et al. 2019

Preprint

1 Inpp5e attenuates Sonic hedgehog signal transduction through a combination of positive and 2 negative regulatory roles that likely control the relative timing of Gli processing. 3 4 Abstract 5 6 Sonic hedgehog (Shh) signal transduction specifies ventral cell fates in the neural tube7 and is mediated by the Gli transcription factors that play both activator (GliA) and repressor 8 (GliR) roles. Cilia are essential for Shh signal transduction and the ciliary phosphatidylinositol 9 phosphatase, Inpp5e, is linked to Shh regulation. In the course of a forward genetic screen for 10 recessive mouse mutants, we identified a functional null allele of Inpp5e, ridge top (rdg), with 11 expanded ventral neural cell fates at E10.5. By E12.5, Inpp5e rdg/rdg embryos displayed normal 12 neural patterning and this correction over time required Gli3, the predominant repressor in 13 neural patterning. Inpp5e rdg function largely depended on the presence of cilia and on 14 Smoothened, the obligate transducer of Shh signaling, indicating Inpp5e functions within the 15 cilium to regulate the pathway. These data indicate that Inpp5e plays a more complicated role in 16 Shh signaling than previously appreciated. We propose that Inpp5e attenuates Shh signaling in 17