An Atypical Parvovirus Drives Chronic Tubulointerstitial Nephropathy and Kidney Fibrosis.

The occurrence of a spontaneous nephropathy with intranuclear inclusions in laboratory mice has puzzled pathologists for over 4 decades, because its etiology remains elusive. The condition is more severe in immunodeficient animals, suggesting an infectious cause. Using metagenomics, we identify the causative agent as an atypical virus, termed "mouse kidney parvovirus" (MKPV), belonging to a divergent genus of Parvoviridae. MKPV was identified in animal facilities in Australia and North America, is transmitted via a fecal-oral or urinary-oral route, and is controlled by the adaptive immune system. Detailed analysis of the clinical course and histopathological features demonstrated a stepwise progression of pathology ranging from sporadic tubular inclusions to tubular degeneration and interstitial fibrosis and culminating in renal failure. In summary, we identify a widely distributed pathogen in laboratory mice and establish MKPV-induced nephropathy as a new tool for elucidating mechanisms of tubulointerstitial fibrosis that shares molecular features with chronic kidney disease in humans.

Oligonephronia: another piece in the CKDu jigsaw?

Rates of chronic kidney disease of unknown etiology are high in Aguascalientes, Mexico. Kidneys of adolescents are small by ultrasonography, compatible with oligonephronia, whereas proteinuria and higher estimated glomerular filtration rates and blood pressures among those with relatively higher kidney volumes probably flag relatively greater degrees of compensatory hypertrophy. Glomerulomegaly and podocytopathy, and later segmental glomerulosclerosis in biopsies, suggest a cascade driven by nephron deficiency. Better measures of glomerular number and volume should improve understanding, facilitate risk assessment, and guide interventions.

Podocyte density as a predictor of long-term kidney outcome in obesity-related glomerulopathy.

Glomerulomegaly and focal segmental glomerulosclerosis are histopathological hallmarks of obesity-related glomerulopathy (ORG). Podocyte injury and subsequent depletion are regarded as key processes in the development of these glomerular lesions in patients with ORG, but their impact on long-term kidney outcome is undetermined. Here, we correlated clinicopathological findings and podocyte depletion retrospectively in patients with ORG. Relative (podocyte density) and absolute (podocyte number per glomerulus) measures of podocyte depletion were estimated using model-based stereology in 46 patients with ORG. The combined endpoint of kidney outcomes was defined as a 30% decline in estimated glomerular filtration rate (eGFR) or kidney failure. Patients with lower podocyte density were predominantly male and had larger body surface area, greater proteinuria, fewer non-sclerotic glomeruli, larger glomeruli and higher single-nephron eGFR. During a median follow-up of 4.1 years, 18 (39%) patients reached endpoint. Kidney survival in patients with lower podocyte density was significantly worse than in patients with higher podocyte density. However, there was no difference in kidney survival between patient groups based on podocyte number per glomerulus. Cox hazard analysis showed that podocyte density, but not podocyte number per glomerulus, was associated with the kidney outcomes after adjustment for clinicopathological confounders. Thus, our study demonstrates that a relative depletion of podocytes better predicts long-term kidney outcomes than does absolute depletion of podocytes. Hence, the findings implicate mismatch between glomerular enlargement and podocyte number as a crucial determinant of disease progression in ORG.

Associations between nephron number and podometrics in human kidneys.

Podocyte loss and resultant nephron loss are common processes in the development of glomerulosclerosis and chronic kidney disease. While the cortical distribution of glomerulosclerosis is known to be non-uniform, the relationship between the numbers of non-sclerotic glomeruli (NSG), podometrics and zonal differences in podometrics remain incompletely understood. To help define this, we studied autopsy kidneys from 50 adults with median age 68 years and median eGFR 73.5 mL/min/1.73m2 without apparent glomerular disease in a cross-sectional analysis. The number of NSG per kidney was estimated using the physical dissector/fractionator combination, while podometrics were estimated using model-based stereology. The number of NSG per kidney was directly correlated with podocyte number per tuft and podocyte density. Each additional 100,000 NSG per kidney was associated with 26 more podocytes per glomerulus and 16 podocytes per 106 µm3 increase in podocyte density. These associations were independent of clinical factors and cortical zone. While podocyte number per glomerulus was similar in the three zones, superficial glomeruli were the smallest and had the highest podocyte density but smallest podocytes. Increasing age and hypertension were associated with lower podocyte number, with age mostly affecting superficial glomeruli, and hypertension mostly affecting juxtamedullary glomeruli. Thus, in this first study to report a direct correlation between the number of NSG and podometrics, we suggest that podocyte number is decreasing in NSG of individuals losing nephrons. However, another possible interpretation may be that more nephrons might protect against further podocyte loss.

The ability of remaining glomerular podocytes to adapt to the loss of their neighbours decreases with age.

Progressive podocyte loss is a feature of healthy ageing. While previous studies have reported age-related changes in podocyte number, density and size and associations with proteinuria and glomerulosclerosis, few studies have examined how the response of remaining podocytes to podocyte depletion changes with age. Mild podocyte depletion was induced in PodCreiDTR mice aged 1, 6, 12 and 18 months via intraperitoneal administration of diphtheria toxin. Control mice received intraperitoneal vehicle. Podometrics, proteinuria and glomerular pathology were assessed, together with podocyte expression of p-rp-S6, a phosphorylation target that represents activity of the mammalian target of rapamycin (mTOR). Podocyte number per glomerulus did not change in control mice in the 18-month time period examined. However, control mice at 18 months had the largest podocytes and the lowest podocyte density. Podocyte depletion at 1, 6 and 12 months resulted in mild albuminuria but no glomerulosclerosis, whereas similar levels of podocyte depletion at 18 months resulted in both albuminuria and glomerulosclerosis. Following podocyte depletion at 6 and 12 months, the number of p-rp-S6 positive podocytes increased significantly, and this was associated with an adaptive increase in podocyte volume. However, at 18 months of age, remaining podocytes were unable to further elevate mTOR expression or undergo hypertrophic adaptation in response to mild podocyte depletion, resulting in marked glomerular pathology. These findings demonstrate the importance of mTORC1-mediated podocyte hypertrophy in both physiological (ageing) and adaptive settings, highlighting a functional limit to podocyte hypertrophy reached under physiological conditions.

Smad4 promotes diabetic nephropathy by modulating glycolysis and OXPHOS.

Diabetic nephropathy (DN) is the leading cause of end-stage kidney disease. TGF-ß1/Smad3 signalling plays a major pathological role in DN; however, the contribution of Smad4 has not been examined. Smad4 depletion in the kidney using anti-Smad4 locked nucleic acid halted progressive podocyte damage and glomerulosclerosis in mouse type 2 DN, suggesting a pathogenic role of Smad4 in podocytes. Smad4 is upregulated in human and mouse podocytes during DN. Conditional Smad4 deletion in podocytes protects mice from type 2 DN, independent of obesity. Mechanistically, hyperglycaemia induces Smad4 localization to mitochondria in podocytes, resulting in reduced glycolysis and oxidative phosphorylation and increased production of reactive oxygen species. This operates, in part, via direct binding of Smad4 to the glycolytic enzyme PKM2 and reducing the active tetrameric form of PKM2. In addition, Smad4 interacts with ATPIF1, causing a reduction in ATPIF1 degradation. In conclusion, we have discovered a mitochondrial mechanism by which Smad4 causes diabetic podocyte injury.

Podometrics in Japanese Living Donor Kidneys: Associations with Nephron Number, Age, and Hypertension.

BACKGROUND: Podocyte depletion, low nephron number, aging, and hypertension are associated with glomerulosclerosis and CKD. However, the relationship between podometrics and nephron number has not previously been examined. METHODS: To investigate podometrics and nephron number in healthy Japanese individuals, a population characterized by a relatively low nephron number, we immunostained single paraffin sections from 30 Japanese living-kidney donors (median age, 57 years) with podocyte-specific markers and analyzed images obtained with confocal microscopy. We used model-based stereology to estimate podometrics, and a combined enhanced-computed tomography/biopsy-specimen stereology method to estimate nephron number. RESULTS: The median number of nonsclerotic nephrons per kidney was 659,000 (interquartile range [IQR], 564,000-825,000). The median podocyte number and podocyte density were 518 (IQR, 428-601) per tuft and 219 (IQR, 180-253) per 106µm3, respectively; these values are similar to those previously reported for other races. Total podocyte number per kidney (obtained by multiplying the individual number of nonsclerotic glomeruli by podocyte number per glomerulus) was 376 million (IQR, 259-449 million) and ranged 7.4-fold between donors. On average, these healthy kidneys lost 5.63 million podocytes per kidney per year, with most of this loss associated with glomerular loss resulting from global glomerulosclerosis, rather than podocyte loss from healthy glomeruli. Hypertension was associated with lower podocyte density and larger podocyte volume, independent of age. CONCLUSIONS: Estimation of the number of nephrons, podocytes, and other podometric parameters in individual kidneys provides new insights into the relationships between these parameters, age, and hypertension in the kidney. This approach might be of considerable value in evaluating the kidney in health and disease.

Podocyte endowment and the impact of adult body size on kidney health.

Low birth weight is a risk factor for chronic kidney disease, whereas adult podocyte depletion is a key event in the pathogenesis of glomerulosclerosis. However, whether low birth weight due to poor maternal nutrition is associated with low podocyte endowment and glomerulosclerosis in later life is not known. Female Sprague-Dawley rats were fed a normal-protein diet (NPD; 20%) or low-protein diet (LPD; 8%), to induce low birth weight, from 3 wk before mating until postnatal day 21 (PN21), when kidneys from some male offspring were taken for quantitation of podocyte number and density in whole glomeruli using immunolabeling, tissue clearing, and confocal microscopy. The remaining offspring were fed a normal- or high-fat diet until 6 mo to induce catch-up growth and excessive weight gain, respectively. At PN21, podocyte number per glomerulus was 15% lower in low birth weight (LPD) than normal birth weight (NPD) offspring, with this deficit greater in outer glomeruli. Surprisingly, podocyte number in LPD offspring increased in outer glomeruli between PN21 and 6 mo, although an overall 9% podocyte deficit persisted. Postnatal fat feeding to LPD offspring did not alter podometric indexes or result in glomerular pathology at 6 mo, whereas fat feeding in NPD offspring was associated with far greater body and fat mass as well as podocyte loss, reduced podocyte density, albuminuria, and glomerulosclerosis. This is the first report that maternal diet can influence podocyte endowment. Our findings provide new insights into the impact of low birth weight, podocyte endowment, and postnatal weight on podometrics and kidney health in adulthood.NEW & NOTEWORTHY The present study shows, for the first time, that low birth weight as a result of maternal nutrition is associated with low podocyte endowment. However, a mild podocyte deficit at birth did not result in glomerular pathology in adulthood. In contrast, postnatal podocyte loss in combination with excessive body weight led to albuminuria and glomerulosclerosis. Taken together, these findings provide new insights into the associations between birth weight, podocyte indexes, postnatal weight, and glomerular pathology.

Clearly imaging and quantifying the kidney in 3D.

For decades, measurements of kidney microanatomy using 2-dimensional sections has provided us with a detailed knowledge of kidney morphology under physiological and pathological conditions. However, the rapid development of tissue clearing methods in recent years, in combination with the development of novel 3-dimensional imaging modalities have provided new insights into kidney structure and function. This review article describes a range of novel insights into kidney development and disease obtained recently using these new methodological approaches. For example, in the developing kidney these approaches have provided new understandings of ureteric branching morphogenesis, nephron progenitor cell proliferation and commitment, interactions between ureteric tip cells and nephron progenitor cells, and the establishment of nephron segmentation. In whole adult mouse kidneys, tissue clearing combined with light sheet microscopy can image and quantify the total number of glomeruli, a major breakthrough in the field. Similar approaches have provided new insights into the structure of the renal vasculature and innervation, tubulointerstitial remodeling, podocyte loss and hypertrophy, cyst formation, the evolution of cellular crescents, and the structure of the glomerular filtration barrier. Many more advances in the understanding of kidney biology and pathology can be expected as additional clearing and imaging techniques are developed and adopted by more investigators.

Your blood pressure might be normal, but what about your podocytes?

Associations among hypertension, podocyte depletion, and chronic kidney disease are well-established, but whether mean arterial pressure (MAP) in the normal range influences podocyte depletion has not been previously examined. In this issue, Naik et al. use non-invasive urinary mRNA analysis to demonstrate that higher podocyte stress and detachment are associated with higher MAP in the normal range. The relationship between blood pressure and podocyte health suddenly got much more interesting.

An inelastic quadrupedal model discovers four-beat walking, two-beat running, and pseudo-elastic actuation as energetically optimal.

It is widely held that quadrupeds choose steady gaits that minimize their energetic cost of transport, but it is difficult to explore the entire range of possible footfall sequences empirically. We present a simple model of a quadruped that can spontaneously produce any of the thousands of planar footfall sequences available to quadrupeds. The inelastic, planar model consists of two point masses connected with a rigid trunk on massless legs. It requires only center of mass position, hind and forelimb proportions and a stride-length to speed relationship as input. Through trajectory optimization of a work and force-rate cost, and a large sample of random initial guesses, we provide evidence for the global optimality of symmetrical four-beat walking at low speeds and two beat running (trotting) at intermediate speeds. Using input parameters based on measurements in dogs (Canis lupus familiaris), the model predicts the correct phase offset in walking and a realistic walk-trot transition speed. It also spontaneously reproduces the double-hump ground reaction force profile observed in walking, and the smooth single-hump profile observed in trotting. Actuation appears elastic, despite the model's lack of springs, suggesting that spring-like locomotory behaviour emerges as an optimal tradeoff between work minimization and force-rate penalties.

Form in the context of function: Fundamentals of an energy effective striding walk, the role of the plantigrade foot and its expected size.

What morphological and functional factors allow for the unique and characteristic upright striding walk of the hominin lineage? Predictive models of locomotion that arise from considering mechanisms of energy loss indicate that collision-like losses at the transition between stance limbs are important determinants of bipedal gait. Theoretical predictions argue that these collisional losses can be reduced by having "functional extra legs" which are physically the heel and the toe part of a single anatomical foot. The ideal spacing for these "functional legs" are up to a quarter of a stride length, depending on the model employed. We evaluate the foot in the context of the dynamics of a bipedal system and compare predictions of optimal foot size against empirical data from modern humans, the Laetoli footprint trackways, and chimpanzees walking bipedally. The dynamics-based modeling approach provides substantial insight into how, and why, walking works as it does, even though current models are too simple to make predictions at a level adequate to anticipate specific morphology except at the most general level.

Nanorg Microbial Factories: Light-Driven Renewable Biochemical Synthesis Using Quantum Dot-Bacteria Nanobiohybrids.

Living cells do not interface naturally with nanoscale materials, although such artificial organisms can have unprecedented multifunctional properties, like wireless activation of enzyme function using electromagnetic stimuli. Realizing such interfacing in a nanobiohybrid organism (or nanorg) requires (1) chemical coupling via affinity binding and self-assembly, (2) the energetic coupling between optoelectronic states of artificial materials with the cellular process, and (3) the design of appropriate interfaces ensuring biocompatibility. Here we show that seven different core-shell quantum dots (QDs), with excitations ranging from ultraviolet to near-infrared energies, couple with targeted enzyme sites in bacteria. When illuminated by light, these QDs drive the renewable production of different biofuels and chemicals using carbon-dioxide (CO2), water, and nitrogen (from air) as substrates. These QDs use their zinc-rich shell facets for affinity attachment to the proteins. Cysteine zwitterion ligands enable uptake through the cell, facilitating cell survival. Together, these nanorgs catalyze light-induced air-water-CO2 reduction with a high turnover number (TON) of ∼106-108 (mols of product per mol of cells) to biofuels like isopropanol (IPA), 2,3-butanediol (BDO), C11-C15 methyl ketones (MKs), and hydrogen (H2); and chemicals such as formic acid (FA), ammonia (NH3), ethylene (C2H4), and degradable bioplastics polyhydroxybutyrate (PHB). Therefore, these resting cells function as nanomicrobial factories powered by light.

Novel 3D analysis using optical tissue clearing documents the evolution of murine rapidly progressive glomerulonephritis.

Recent developments in optical tissue clearing have been difficult to apply for the morphometric analysis of organs with high cellular content and small functional structures, such as the kidney. Here, we establish combinations of genetic and immuno-labelling for single cell identification, tissue clearing and subsequent de-clarification for histoimmunopathology and transmission electron microscopy. Using advanced light microscopy and computational analyses, we investigated a murine model of crescentic nephritis, an inflammatory kidney disease typified by immune-mediated damage to glomeruli leading to the formation of hypercellular lesions and the rapid loss of kidney function induced by nephrotoxic serum. Results show a graded susceptibility of the glomeruli, significant podocyte loss and capillary injury. These effects are associated with activation of parietal epithelial cells and formation of glomerular lesions that may evolve and obstruct the kidney tubule, thereby explaining the loss of kidney function. Thus, our work provides new high-throughput endpoints for the analysis of complex tissues with single-cell resolution.

Determinants of optimal leg use strategy: horizontal to vertical transition in the parkour wall climb.

This study examined the mechanics of the horizontal to vertical transition used by parkour athletes in wall climbing. We used this task as an alternative to normal running - where the functional options differ substantially - exposing the movement control priorities required to successfully complete the task. Ground reaction forces were measured in several expert parkour athletes and centre of mass trajectory was calculated from force plates embedded in the ground and the wall. Empirical measures were compared with movements predicted by a work-based control optimization model. The model captured the fundamental dynamics of the transition and therefore allowed an exploration of parameter sensitivity for success at the manoeuvre (run-up speed, foot placement, etc.). The optimal transition of both the model and the parkour athletes used a common intermediate run-up speed and appears determined largely by a trade-off between positive and negative leg work that accomplishes the task with minimum overall work.

Load carrying with flexible bamboo poles: optimization of a coupled oscillator system.

In Asia, flexible bamboo poles are routinely used to carry substantial loads on the shoulder. Various advantages have been attributed to this load-carrying strategy (e.g. reduced energy consumption), but experimental evidence remains inconsistent - possibly because carriers in previous studies were inexperienced. Theoretical models typically neglect the individual's capacity to optimize interactions with the oscillating load, leaving the complete dynamics underexplored. This study used a trajectory optimization model to predict gait adaptations that minimize work-based costs associated with carrying compliant loads and compared the outcomes with naturally selected gait adaptations of experienced pole carriers. Gait parameters and load interactions (e.g. relative amplitude and frequency, phase) were measured in rural farmworkers in Vietnam. Participants carried a range of loads with compliant and rigid poles and the energetic consequences of step frequency adjustments were evaluated using the model. When carrying large loads, the empirical step frequency changes associated with pole type (compliant versus rigid) were largely consistent with model predictions, in terms of direction (increase or decrease) and magnitude (by how much). Work-minimizing strategies explain changes in leg compliance, harmonic frequency oscillations and fluctuations in energetic cost associated with carrying loads on a compliant bamboo pole.

Biopsy-based estimation of total nephron number in Japanese living kidney donors.

BACKGROUND: Increasing evidence suggests that individuals with low nephron number have an increased lifetime risk of renal insufficiency, thereby emphasizing the importance of evaluating total nephron number in each individual. In recent years, new methods have been described for estimating human total nephron number using a combination of image analysis and renal biopsy, though the reproducibility and accuracy of these methods remain uncertain. This study estimated total nephron number in healthy Japanese subjects using such a method. METHODS: Implantation biopsies from 44 living kidney donors were analyzed. Using pre-donation contrast CT angiograms, transplantation donor kidneys were three-dimensionally reconstructed, and total renal cortical volume was estimated. Total nephron number was estimated based on glomerular density in biopsy specimens and total renal cortical volume. The obtained results were analyzed in relation to clinical variables and compared with those of a previously reported Japanese autopsy study. RESULTS: The estimated non-sclerotic and total numbers of glomeruli in this cohort were 650,000 ± 220,000 and 710,000 ± 220,000 (mean ± SD) per kidney. Non-sclerotic glomerular number ranged from 280,000 to 1,220,000 per kidney (4.4-fold) and correlated directly with eGFR (r = 0.328, p = 0.030) and inversely with age (r = - 0.355, p = 0.018). CONCLUSION: The estimated total nephron number obtained in the present study was 25% less than that reported in American living kidney donors obtained using the same procedure and similar to that obtained in a previous Japanese autopsy study using the disector/fractionator method. These results confirm the feasibility of a combined CT angiography and biopsy-based method to estimate total nephron number in humans.

Near-Infrared-Light-Triggered Antimicrobial Indium Phosphide Quantum Dots.

The emergence of multidrug-resistant (MDR) pathogens represents one of the most urgent global public health crises. Light-activated quantum dots (QDs) are alternative antimicrobials, with efficient transport, low cost, and therapeutic efficacy, and they can act as antibiotic potentiators, with a mechanism of action orthogonal to small-molecule drugs. Furthermore, light-activation enhances control over the spatiotemporal release and dose of the therapeutic superoxide radicals from QDs. However, the limited deep-tissue penetration of visible light needed for QD activation, and concern over trace heavy metals, have prevented further translation. Herein, we report two indium phosphide (InP) QDs that operate in the near-infrared and deep-red light window, enabling deeper tissue penetration. These heavy-metal-free QDs eliminate MDR pathogenic bacteria, while remaining non-toxic to host human cells. This work provides a pathway for advancing QD nanotherapeutics to combat MDR superbugs.

Maternal low-protein diet programmes low ovarian reserve in offspring

The ovarian reserve of primordial follicle oocytes is formed during in utero development and represents the entire supply of oocytes available to sustain female fertility. Maternal undernutrition during pregnancy and lactation diminishes offspring ovarian reserve in rats. In mice, maternal oocyte maturation is also susceptible to undernutrition, causing impaired offspring cardiovascular function. We aimed to determine whether programming of the ovarian reserve is impacted in offspring when maternal undernutrition extends from preconception oocyte development through to weaning. C57BL6/J female mice were fed normal protein (20%) or low-protein (8%) diet during preconception, pregnancy and lactation periods. Maternal ovaries were harvested at weaning and offspring ovaries were collected at postnatal day (PN)21 and 24 weeks of age. Total follicle estimates were obtained by histologically sampling one ovary per animal (n = 5/group). There was no impact of diet on maternal follicle numbers. However, in offspring, maternal protein restriction significantly depleted primordial follicles by 37% at PN21 and 51% at 24 weeks (P < 0.05). There were no effects of diet on other follicle classes. Histological analysis showed no differences in the proportion of proliferative follicles (pH3 positive), but increased atresia (cleaved caspase-3-positive, or TUNEL-positive) was detected in ovaries of protein-restricted offspring at both ages (P < 0.05). Our data show that maternal diet during the preconception period, in utero development and early life has significant impacts on follicle endowment and markers of follicle health later in life. This highlights the need for further investigation into the importance of maternal preconception diet for offspring reproductive development and health.