Biology subjects

Chandrasekar, I.

Publications and source records attributed to Chandrasekar, I..

6 recordsLinked to original sources

bioRxiv2026

Myofibroblast- specific autophagy drives cyst growth in autosomal dominant polycystic kidney disease

BackgroundAutosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive cyst expansion, fibrosis and inflammation, leading to kidney failure. Myofibroblasts (MFs) often accumulate around cysts and promote fibrosis and cyst growth, but the cellular mechanisms enabling their pro-cystogenic activity remain unclear. Here we examined the role of autophagy within MFs, on their paracrine stimulation of cyst expansion in ADPKD. MethodsAutophagy was assessed in human ADPKD nephrectomy tissue, primary human ADPKD renal myofibroblasts (ADPKD-MFs) and male RC/RC mouse model of ADPKD using immunostaining, LC3/p62 analyses, and transmission electron microscopy. Autophagy in MFs was inhibited pharmacologically in ADPKD-MFs, or by conditional Atg5 deletion in PDGFR{beta}-expressing renal stromal cells in RC/RC (RC/RC;Atg5KO) and wild type (WT;Atg5KO) mice. ResultsIn human and mouse ADPKD kidneys, we detected LC3 puncta and autophagic organelles within SMA-expressing MFs. Inhibition of autophagy in ADPKD-MFs blocked their paracrine stimulation of cyst epithelial cell proliferation in vitro. RC/RC;Atg5KO mice showed significantly reduced cystic growth, fibrosis, MF abundance, and improved kidney function. WT;Atg5KO mice showed no abnormalities in kidney structure or function. Targeted metabolomics performed on ADPKD cyst epithelial-cell conditioned media (ADPKD-ECs CM) revealed moderate increase in lactate levels compared to normal human kidney epithelial-cell conditioned media. Furthermore, lactate treatment stabilized hypoxia-inducible factor-1 (HIF1) in myofibroblasts, while pharmacological inhibition of HIF1 reduced the expression of autophagy-related genes and impaired autophagic flux. ConclusionThese findings reveal that autophagy in MFs is a previously unrecognized driver of cyst expansion and fibrosis in ADPKD. Lactate-mediated HIF1 stabilization in MFs promotes autophagy that is required for their paracrine stimulation of cyst epithelial growth. Targeting MF-specific autophagy or its upstream regulators may represent a therapeutic strategy to limit cyst growth and fibrosis in ADPKD.

molecular biology↗

bioRxiv2026

Tannic acid fortifies extracellular matrix against dicarbonyl stress

Methylglyoxal (MGO), a highly reactive dicarbonyl metabolite that accumulates in diabetes and aging, causes tissue dyshomeostasis, for which therapeutic interventions are limited. Herein, we investigate the potential of tannic acid (TA) in fortifying organ and organismal health against MGO. Anatomical disruption in vivo of hydra bodies and ex vivo decellularization of murine mesenteries with MGO suggested an impaired interaction between cells and their extracellular matrix (ECM); however, pretreatment of these systems with TA reversed this effect. We confirmed this through subsequent exposure of control and TA-pretreated mammalian cell-secreted endogenous matrix, Collagen I, and basement membrane matrix to MGO. TA prevented loss of ECM biochemical characteristics and restored perturbed cell adhesion and spreading on these substrata induced by MGO. NMR titrations confirmed TA-bound MGO in a 1:5 stoichiometry, potentially quenching its electrophilic properties. Our study posits TA as a novel candidate for protecting organ and organismal architectures against the histopathological effects of dicarbonyl stress.

biochemistry↗

bioRxiv2024

Kidney collecting duct cell type composition is regulated by Notch signaling via modulation of mTORC1

The plasticity and diversity of cell types with specialized functions likely defines the capacity of multicellular organisms to adapt to physiologic stressors. The kidney collecting ducts contribute to water, electrolyte, and pH homeostasis and are composed of mature intermingled epithelial cell types that are susceptible to transdifferentiate. The conversion of kidney collecting duct principal cells to intercalated cells is actively inhibited by Notch signaling to ensure urine concentrating capability. Here we identify Hes1, a target of Notch signaling, allows for maintenance of functionally distinct epithelial cell types within the same microenvironment by regulating mechanistic target of rapamycin complex 1 (mTORC1) activity. Hes1 directly represses the expression of insulin receptor substrate 1 (Irs1), an upstream component of mTOR pathway and suppresses mTORC1 activity in principal cells. Genetic inactivation of tuberous sclerosis complex 2 (Tsc2) to increase mTORC1 activity in mature principal cells is sufficient to promote acquisition of intercalated cell properties, while inhibition of mTORC1 in adult kidney epithelia suppresses intercalated cell properties. Considering that mTORC1 integrates environmental cues, the linkage of functionally distinct epithelial cell types to mTORC1 activity levels likely allows for cell plasticity to be regulated by physiologic and metabolic signals and the ability to sense/transduce these signals.

developmental biology↗

bioRxiv2020

VARIATION AND SELECTION IN AXON NAVIGATION THROUGH MICROTUBULE-DEPENDENT STEPWISE GROWTH CONE ADVANCE

Myosin II (MII) activity is required for elongating mammalian sensory axons to change speed and direction in response to Nerve Growth Factor (NGF) and laminin-1 (LN). NGF signaling induces faster outgrowth on LN through regulation of actomyosin restraint of microtubule advance into the growth cone periphery. It remains unclear whether growth cone turning on LN works through the same mechanism and, if it does, how the mechanism produces directed advance. Using a novel method for substrate patterning, we tested how directed advance occurs on LN by creating a gap immediately in front of a growth cone advancing on a narrow LN path. The growth cone stopped until an actin-rich protrusion extended over the gap, adhered to LN, and became stabilized. Stepwise advance over the gap was triggered by microtubule +tip entry up to the adhesion site of the protrusion and was independent of traction force pulling. We found that the probability of microtubule entry is regulated at the level of the individual protrusion and is sensitive to the rate of microtubule polymerization and the rate of rearward actin flow as controlled by adhesion-cytoskeletal coupling and MII. We conclude that growth cone navigation is an iterative process of variation and selection. Growth cones extend leading edge actin-rich protrusions that adhere transiently (variation). Microtubule entry up to an adhesion site stabilizes a protrusion (selection) leading to engorgement, consolidation, protrusive activity distal to the adhesion site, and stepwise growth cone advance. The orientation of the protrusion determines the direction of advance.

neuroscience↗

bioRxiv2019

Notch signaling regulates Akap12 expression and primary cilia length during renal tubule morphogenesis.

Alagille syndrome patients present with loss of function mutations in either JAG1 or NOTCH2. About 40-50% of patients have kidney abnormalities, with multi-cystic, dysplastic kidneys being one of the more frequent kidney defects. Additionally, gain-of-function mutations in NOTCH2 are associated with cystic kidneys in Hajdu-Cheney syndrome patients. Conditional inactivation of Notch1, Notch2, or RBPJ within the nephrogenic lineage impairs nephrogenesis and produces proximal tubule cysts in mice. How perturbations in Notch signaling cause renal tubular cysts remains unclear. Here we have determined that inhibition of Notch signaling in the kidney increases Akap12 expression. Ectopic expression of Akap12 in renal epithelia results in abnormally long primary cilia similar to those observed in Notch-signal-deficiency. Both loss of Notch signaling and elevated Akap12 expression disrupt the ability of renal epithelial cells to form spherical structures with a single lumen when grown embedded in matrix. We conclude that Notch signaling regulates Akap12 expression to ensure normal primary cilia length and renal epithelial morphogenesis, and suggest that diseases associated with defective Notch signaling, such as Alagille syndrome, maybe mechanistically related to ciliopathies.\n\nTranslational StatementThe current study examines how a reduction in Notch signaling results in abnormal renal tubule formation, as occurs in Alagille Syndrome patients with mutations in JAG1 or NOTCH2. The finding that reduced Notch signaling results in abnormally long cilia is suggestive that some of the clinical manifestations in Alagille Syndrome, such as small cystic kidneys, may originate due to defective cilia function. Linking Notch to primary cilia also opens up the possibility that coinheritance of mutations in ciliopathy genes along with a mutation in JAG1 or NOTCH2 may enhance the severity of the clinical phenotypes such as cystic kidney disease and may explain the variable occurrence and onset of kidney disease among Alagille Syndrome patients.

cell biology↗

bioRxiv2019

Myosin II Tension Sensors Visualize Force Generation within the Actin Cytoskeleton in Living Cells

Type II myosin motors generate cytoskeletal forces that are central to cell division, embryogenesis, muscle contraction, and many other cellular functions. However, at present there is no method that can directly measure the forces generated by myosins in living cells. Here we describe a Forster resonance energy transfer (FRET)-based tension sensor that can measure forces generated by Nonmuscle Myosin IIB (NMIIB) in living cells with piconewton (pN) sensitivity. Fluorescence lifetime imaging microscopy (FLIM)-FRET measurements indicate that the forces generated by NMIIB exhibit significant spatial and temporal heterogeneity, with inferred tensions that vary widely in different regions of the cell. This initial report highlights the potential utility of myosin-based tension sensors in elucidating the roles of cytoskeletal contractility in a wide variety of contexts.

cell biology↗