Acute kidney injury (AKI) is considered largely reversible based on the capacity of surviving tubular cells to dedifferentiate and replace lost cells via cell division. Here we show by tracking individual tubular cells in conditional Pax8/Confetti mice that kidney function is  recovered after AKI despite substantial tubular cell loss. Cell cycle and ploidy analysis upon AKI in conditional Pax8/FUCCI2aR mice and human biopsies identify endocycle-mediated hypertrophy of tubular cells. By contrast, a small subset of Pax2+ tubular progenitors enriches via higher stress resistance and clonal expansion and regenerates necrotic tubule segments, a process that can be enhanced by suitable drugs. Thus,  renal functional recovery upon AKI involves remnant tubular cell hypertrophy via endocycle and limited progenitor-driven regeneration that can be pharmacologically enhanced.

Since amyotrophic lateral sclerosis cases exhibit significant heterogeneity, we aim to investigate the association of lipid composition of plasma and cerebrospinal fluid with amyotrophic lateral sclerosis diagnosis, its progression, and clinical characteristics. Lipidome analyses would help to stratify patients on a molecular basis. For this reason, we have analyzed the lipid composition of paired plasma and cerebrospinal fluid samples from amyotrophic lateral sclerosis cases and age-matched non-amyotrophic lateral sclerosis individuals (controls) by comprehensive liquid chromatography coupled to mass spectrometry. The concentrations of neurofilament light chain –an index of neuronal damage- were also quantified in cerebrospinal fluid samples and plasma. Amyotrophic lateral sclerosis vs. control comparison in a moderate stringency mode showed that plasma from cases contains more differential lipids (n = 122 for raw p < 0.05;n=27 for p < 0.01) than cerebrospinal fluid (n = 17 for raw p < 0.05; n = 4 for p < 0.01), with almost no overlapping differential species, mainly characterized by an increased content of triacylglyceride species in plasma and decreased in cerebrospinal fluid. Of note, false discovery rate correction indicated that one of the cerebrospinal fluid lipids (monoacylglycerol 18:0) had high statistic robustness (false discovery rate-p<0.01). Plasma lipidomes also varied significantly with the main involvement at onset (bulbar, spinal, or respiratory). Notably, faster progression cases showed particular lipidome fingerprints featured by decreased triacylclycerides and specific phospholipids in plasma., with 11 lipids with false discovery rate-p<0.1 (n = 56 lipids in plasma for raw p < 0.01). Lipid species associated with progression rate clustered in a relatively low number of metabolic pathways, mainly triacylglyceride metabolism and glycerophospholipid and sphingolipid biosynthesis. A specific triacylglyceride (68:12) correlated with neurofilament content (r = 0.8, p < 0.008). Thus, the present findings suggest that systemic hypermetabolism –potentially sustained by increased triacylglyceride content- and central nervous system alterations of specific lipid pathways could be associated as modifiers of disease progression. Further, these results confirm biochemical lipid heterogeneity in amyotrophic lateral sclerosis with different presentations and progression, suggesting the use of specific lipid species as potential disease classifiers.

ALS: amyotrophic lateral sclerosis; ATG4B: autophagy related 4B cysteine peptidase; AUC: area under the curve; FTLD: frontotemporal lobar degeneration; iPSC: induced pluripotent stem cells; ROC: receiver operating characteristic; TARDBP: TAR DNA binding protein; RT-qPCR: quantitative RT-PCR.

Damage to the sensory hair cells and the spiral ganglion neurons of the cochlea leads to deafness. Induced pluripotent stem cells (iPSCs) are a promising tool to regenerate the cells in the inner ear that have been affected by pathology or have been lost. To facilitate the clinical application of iPSCs, the reprogramming process should minimize the risk of introducing undesired genetic alterations while conferring the cells the capacity to differentiate into the desired cell type. Currently, reprogramming induced by synthetic mRNAs is considered to be one of the safest ways of inducing pluripotency, as the transgenes are transiently delivered into the cells without integrating into the genome. In this study, we explore the ability of integration-free human-induced pluripotent cell lines that were reprogrammed by mRNAs, to differentiate into otic progenitors and, subsequently, into hair cell and neuronal lineages. hiPSC lines were induced to differentiate by culturing them in the presence of fibroblast growth factors 3 and 10 (FGF3 and FGF10). Progenitors were identified by quantitative microscopy, based on the coexpression of otic markers PAX8, PAX2, FOXG1, and SOX2. Otic epithelial progenitors (OEPs) and otic neuroprogenitors (ONPs) were purified and allowed to differentiate further into hair cell-like cells and neurons. Lineages were characterised by immunocytochemistry and electrophysiology. Neuronal cells showed inward Na+ (INa) currents and outward (Ik) and inward K+ (IK1) currents while hair cell-like cells had inward IK1 and outward delayed rectifier K+ currents, characteristic of developing hair cells. We conclude that human-induced pluripotent cell lines that have been reprogrammed using nonintegrating mRNAs are capable to differentiate into otic cell types.