A role for the inositol kinase Ipk1 in ciliary beating and length maintenance

Cilia project from cells as membranous extensions, with microtubule structural cores assembling from basal bodies by intraflagellar transport (IFT). Here, we report a ciliary role for the inositol 1,3,4,5,6-pentakisphosphate 2-kinase (Ipk1) that generates inositol hexakisphosphate. In zebrafish embryos, reducing Ipk1 levels inhibited ciliary beating in Kupffer''s vesicle and decreased ciliary length in the spinal canal, pronephric ducts, and Kupffer''s vesicle. Electron microscopy showed that ciliary axonemal structures were not grossly altered. However, coincident knockdown of Ipk1 and IFT88 or IFT57 had synergistic perturbations. With GFP-Ipk1 enriched in centrosomes and basal bodies, we propose that Ipk1 plays a previously uncharacterized role in ciliary function.     

A role for axon–glial interactions and Netrin-G1 signaling in the formation of low-threshold mechanoreceptor end organs

Low-threshold mechanoreceptors (LTMRs) and their cutaneous end organs convert light mechanical forces acting on the skin into electrical signals that propagate to the central nervous system. In mouse hairy skin, hair follicle–associated longitudinal lanceolate complexes, which are end organs comprising LTMR axonal endings that intimately associate with terminal Schwann cell (TSC) processes, mediate LTMR responses to hair deflection and skin indentation. Here, we characterized developmental steps leading to the formation of Aβ rapidly adapting (RA)-LTMR and Aδ-LTMR lanceolate complexes. During early postnatal development, Aβ RA-LTMRs and Aδ-LTMRs extend and prune cutaneous axonal branches in close association with nascent TSC processes. Netrin-G1 is expressed in these developing Aβ RA-LTMR and Aδ-LTMR lanceolate endings, and Ntng1 ablation experiments indicate that Netrin-G1 functions in sensory neurons to promote lanceolate ending elaboration around hair follicles. The Netrin-G ligand (NGL-1), encoded by Lrrc4c, is expressed in TSCs, and ablation of Lrrc4c partially phenocopied the lanceolate complex deficits observed in Ntng1 mutants. Moreover, NGL-1–Netrin-G1 signaling is a general mediator of LTMR end organ formation across diverse tissue types demonstrated by the fact that Aβ RA-LTMR endings associated with Meissner corpuscles and Pacinian corpuscles are also compromised in the Ntng1 and Lrrc4c mutant mice. Thus, axon–glia interactions, mediated in part by NGL-1–Netrin-G1 signaling, promote LTMR end organ formation.

Touch sensation is an integral component of our sensory experience, allowing us to perceive and respond to the physical world. Light touch is mediated by morphologically and physiologically distinct classes of low-threshold mechanosensory neurons (LTMRs), which detect a range of innocuous tactile stimuli and convey their signals from the skin to the central nervous system (1, 2). The cell bodies of LTMRs are located in dorsal root ganglia (DRG) and cranial sensory ganglia. LTMRs have one axonal branch that extends to the skin and associates with different end organs and another branch that projects to the central nervous system and forms synapses onto second-order neurons in the spinal cord dorsal horn and brainstem (3). LTMRs have been classified as Aβ-, Aδ-, or C-LTMRs based on their action potential conduction velocities (4, 5). Aβ-LTMRs are heavily myelinated and Aδ-LTMRs are lightly myelinated, exhibiting rapid and intermediate conduction velocities, respectively. C-LTMRs are unmyelinated and have a slow conduction velocity. LTMRs are also classified as slowly, intermediately, or rapidly adapting (SA-, IA-, and RA-, respectively) according to their firing patterns in response to sustained indentation of the skin (3).LTMR subtypes exhibit distinct intrinsic physiological properties and unique axonal endings associated with end organ structures across different skin types. The cutaneous axonal endings of Aβ RA-LTMRs form longitudinal lanceolate endings that enwrap hair follicles in hairy skin, terminate within Meissner corpuscles in glabrous (nonhairy) skin, or form Pacinian corpuscles located in the deep dermis or around bones (3). In mouse back hairy skin, Aβ RA-LTMR lanceolate endings form around guard hairs, which account for ∼1% of back skin hairs, and awl/auchene hairs. Aδ-LTMRs and C-LTMRs also form lanceolate endings, but unlike Aβ RA-LTMRs they are associated exclusively with nonguard hairs (awl/auchene and zigzag hairs) (6). These lanceolate ending structures are assumed to endow LTMRs with high sensitivity to hair deflection, skin indentation, and skin stroking (3). Investigating the formation of lanceolate endings associated with guard hairs and nonguard hairs will provide insights into mechanisms of development and regeneration of sensory neurons and their end organs that underlie touch. Somatosensory neuron axon terminals are encased by terminal Schwann cells (TSCs), which are a specialized group of nonmyelinating Schwann cells (2, 7). Indeed, light and electron microscopic studies reveal that lanceolate endings are arranged parallel to the hair follicle’s long axis, and each lanceolate ending is surrounded by TSC processes (8–11). Similar to lanceolate endings in hairy skin, the LTMR endings associated with Meissner corpuscles and Pacinian corpuscles are also wrapped by nonmyelinating Schwann cells, called lamellar cells (12–18).LTMR innervation of hairy skin occurs in parallel with skin and hair follicle morphogenesis (19–22). Beginning on approximately embryonic day 14.5 (E14.5), primary guard hair keratinocyte precursor cells elongate to form hair follicle placodes and then proliferate and invaginate to form hair follicles (23). Secondary hair follicle development occurs in two waves: awl/auchene hairs develop at approximately E16.5, and zigzag hairs develop around birth (E18–postnatal day 1 [P1]) (24). Developing hair follicles can release extrinsic cues to instruct the formation of lanceolate complexes. For example, keratinocytes on the caudal side of hair follicles express BDNF and control the polarized targeting of TrkB-expressing Aδ-LTMR endings to the caudal side of hair follicles (25). Moreover, hair follicle epidermal stem cells deposit EGFL6, an ECM protein, into the collar matrix, to regulate the proper patterning of lanceolate complexes (26). However, the precise timing of LTMR innervation of hair follicles, whether LTMR axons undergo pruning during hair follicle innervation, the nature of the relationship between developing lanceolate endings and nascent TSCs, and molecular cues that instruct lanceolate ending morphological maturation remain unexplored.Netrin-G1, encoded by Ntng1, is a member of the family of glycosyl-phosphatidylinositol (GPI)-anchored cell adhesion molecules. Netrin-G1 can promote synapse formation, microglial accumulation along axons, axonal outgrowth, and laminar organization of dendrites (27–30). Moreover, Netrin-G1 and its relative Netrin-G2 can localize to presynaptic membranes and instruct the specificity in synaptic connectivity (28, 30–32). In these contexts, Netrin-G1 is considered to function as a cell surface receptor. The Netrin-G1 ligand, NGL-1, which is encoded by Lrrc4c, belongs to a family of postsynaptic adhesion molecules (27, 29, 32–34). Mutations in both Ntng1 and Lrrc4c have been implicated in neurological diseases, including Rett syndrome, schizophrenia, and autism (35–38). Yet, the functions of Netrin-G1 and NGL-1 in peripheral nervous system development have not been established.Here, we used mouse genetic approaches to visualize Aβ RA-LTMRs and Aδ-LTMRs during late embryonic and early postnatal development (25, 39), which allowed us to define the timing of hairy skin innervation and formation of their lanceolate complexes. Aβ RA-LTMR and Aδ-LTMR peripheral innervation patterns are established late embryonically and neonatally, exuberant axonal branches are pruned around birth, and newly formed lanceolate endings associate intimately with nascent TSCs. We found that Netrin-G1 signaling functions in somatosensory neurons to promote proper formation of Aβ RA-LTMR and Aδ-LTMR lanceolate complexes. Lrrc4c, encoding the Netrin-G1 ligand, NGL-1, is expressed in developing TSCs in hairy skin, and its deletion leads to similar, albeit milder, Aβ RA-LTMR and Aδ-LTMR lanceolate ending deficits. Moreover, we observed aberrant Meissner corpuscle and Pacinian corpuscle development in the absence of NGL-1–Netrin-G1 signaling. Our findings delineate LTMR end organ developmental stages and reveal a role for NGL-1–Netrin-G1 signaling between TSCs and LTMR endings in mechanoreceptor end organ formation.     

Tomonaga–Luttinger Spin Liquid and Kosterlitz–Thouless Transition in the Spin-1/2 Branched Chains: The Study of Topological Phase Transition

In the present work, we provide a comprehensive numerical investigation of the magnetic properties and phase spectra of three types of spin-1/2 branched chains consisting of one, two and three side spins per unit block with intra-chain interaction and a uniform inter-chain interaction in the presence of an external magnetic field. In a specific magnetic field interval, the low-temperature magnetization of these chains shows a step-like behavior with a pronounced plateau depending on the strength and the type of intra-chain interaction being ferromagnetic or antiferromagnetic. We demonstrate that when inter-chain interaction J1 is antiferromagnetic and intra-chain interaction J2 is ferromagnetic, the magnetization of the models manifests a smooth increase without a plateau, which is evidence of the existence of a Luttinger-like spin liquid phase before reaching its saturation value. On the other hand, when J1 is ferromagnetic and J2 is antiferromagnetic, the low-temperature magnetization of the chain with two branches shows an intermediate plateau at one-half of the saturation magnetization that breaks a quantum spin liquid phase into two regions. The magnetization of the chain with three branches exhibits two intermediate plateaus and two regions of a quantum spin liquid. We demonstrate that the chains with more than one side spin illustrate in their ground-state phase diagram a Kosterlitz–Thouless transition from a gapful phase to a gapless spin liquid phase.     

Adenosine/adenosine type 1 receptor signaling pathway did not play dominant roles on the influence of sodium–glucose cotransporter 2 inhibitor in the kidney of bovine serum albumin‐overloaded streptozotocin‐induced diabetic mice

Aims/IntroductionSodium–glucose cotransporter 2 inhibitors (SGLT2i) have been shown to display excellent renoprotective effects in diabetic kidney disease with macroalbuminuria/proteinuria. Regarding the renoprotective mechanism of SGLT2i, a sophisticated hypothesis was made by explaining the suppression of glomerular hypertension/hyperfiltration through the adenosine/adenosine type 1 receptor (A1R) signaling‐mediated restoration of the tubuloglomerular feedback mechanism; however, how such A1R signaling is relevant for renoprotection by SGLT2i in diabetic kidney disease with proteinuria has not been elucidated.Materials and MethodsStreptozotocin‐induced diabetic CD‐1 mice were injected with bovine serum albumin (BSA) and treated with SGLT2i in the presence/absence of A1R inhibitor administration.ResultsWe found that the influences of SGLT2i are essentially independent of the activation of A1R signaling in the kidney of BSA‐overloaded streptozotocin‐induced diabetic mice. BSA‐overloaded diabetic mice showed the trend of kidney damage with higher glomerular filtration rate (GFR) and the significant induction of fibrogenic genes, such as transforming growth factor‐β2 and collagen type III. SGLT2i TA‐1887 suppressed diabetes‐induced GFR in BSA‐overloaded diabetic mice was associated with the significant suppression of transforming growth factor‐β2 and collagen type III; A1R‐specific inhibitor 8‐cyclopentyl‐1,3‐dipropylxanthine did not cancel the effects of TA‐1887 on either GFR or associated gene levels. Both TA‐1887 and 8‐cyclopentyl‐1,3‐dipropylxanthine‐treated BSA‐overloaded diabetic mice showed suppressed glycated hemoglobin levels associated with the increased food intake. When analyzing the association among histological evaluation, GFR and potential fibrogenic gene levels, each group of mice showed distinct correlation patterns.ConclusionsA1R signaling activation was not the dominant mechanism on the influence of SGLT2i in the kidney of BSA‐overloaded diabetic mice.     

Notch3 signaling activation in smooth muscle cells promotes extrauterine growth restriction-induced pulmonary hypertension

Background and aimsEarly postnatal life is a critical developmental period that affects health of the whole life. Extrauterine growth restriction (EUGR) causes cardiovascular development problems and diseases, including pulmonary arterial hypertension (PAH). PAH is characterized by proliferation, migration, and anti-apoptosis of pulmonary artery smooth muscle cells (PASMCs). However, the role of PASMCs in EUGR has not been studied. Thus, we hypothesized that PASMCs dysfunction played a role in EUGR-induced pulmonary hypertension.Methods and resultsHere we identified that postnatal nutritional restriction-induced EUGR rats exhibited an elevated mean pulmonary arterial pressure and vascular remodeling at 12 weeks old. PASMCs of EUGR rats showed increased cell proliferation and migration features. In EUGR-induced PAH rats, Notch3 signaling was activated. Relative mRNA and protein expression levels of Notch3 intracellular domain (Notch3 ICD), and Notch target gene Hey1 in PASMCs were upregulated. We further demonstrated that pharmacological inhibition of Notch3 activity by using a γ-secretase inhibitor DAPT, which blocked the cleavage of Notch proteins to ICD peptides, could effectively inhibit PASMC proliferation. Specifically knocked down of Notch3 in rat PASMCs by shRNA restored the abnormal PASMC phenotype in vitro. We found that administration of Notch signaling inhibitor DAPT could successfully reduce mean pulmonary arterial pressure in EUGR rats.ConclusionsThe present study demonstrated that upregulation of Notch3 signaling in PASMCs was crucial for the development of EUGR-induced PAH. Blocking Notch3-Hey1 signaling pathway in PASMCs provides a potential therapeutic target for PAH.