Gaussian curvature dilutes the nuclear lamina, favoring nuclear rupture, especially at high strain rate

Nuclear rupture has long been associated with deficits or defects in lamins, with recent results also indicating a role for actomyosin stress, but key physical determinants of rupture remain unclear. Here, lamin-B stably interacts with the nuclear membrane at sites of low Gaussian curvature yet dilutes at high-curvature to favor rupture, whereas lamin-A depletes similarly but only at high strain-rates. Live cell imaging of lamin-B1 gene-edited cancer cells is complemented by fixed-cell imaging of ruptured nuclei in: iPS-derived cells from progeria patients, cells within beating chick embryo hearts, and cancer cells that develop multiple ruptures in migrating through small pores. Dilution and curvature-dependent rupture fit a parsimonious model of a stiff filament that detaches from a curved surface, suggesting an elastic-type response of lamin-B, but rupture is also modestly suppressed by inhibiting myosin-II and by hypotonic stress, which slow the strain rates. Lamin-A dilution and nuclear rupture likelihood indeed increase above a threshold rate of pulling into small pipettes, suggesting a viscoplastic coupling to the envelope for protection against nuclear rupture.

Disruption of Chromatin Dynamics by Hypotonic Stress Suppresses HR and Shifts DSB Processing to Error-Prone SSA

The processing of DNA double-strand breaks (DSBs) depends on the dynamic characteristics of chromatin. To investigate how abrupt changes in chromatin compaction alter these dynamics and affect DSB processing and repair, we exposed irradiated cells to hypotonic stress (HypoS). Densitometric and chromosome-length analyses show that HypoS transiently decompacts chromatin without inducing histone modifications known from regulated local chromatin decondensation, or changes in Micrococcal Nuclease (MNase) sensitivity. HypoS leaves undisturbed initial stages of DNA-damage-response (DDR), such as radiation-induced ATM activation and H2AX-phosphorylation. However, detection of ATM-pS1981, γ-H2AX and 53BP1 foci is reduced in a protein, cell cycle phase and cell line dependent manner; likely secondary to chromatin decompaction that disrupts the focal organization of DDR proteins. While HypoS only exerts small effects on classical nonhomologous end-joining (c-NHEJ) and alternative end-joining (alt-EJ), it markedly suppresses homologous recombination (HR) without affecting DNA end-resection at DSBs, and clearly enhances single-strand annealing (SSA). These shifts in pathway engagement are accompanied by decreases in HR-dependent chromatid-break repair in the G2-phase, and by increases in alt-EJ and SSA-dependent chromosomal translocations. Consequently, HypoS sensitizes cells to ionizing radiation (IR)-induced killing. We conclude that HypoS-induced global chromatin decompaction compromises regulated chromatin dynamics and genomic stability by suppressing DSB-processing by HR, and allowing error-prone processing by alt-EJ and SSA.

Effect of Chicken Bone Extract Powder on Epididymal Sperm Quality of Male Wistar Rats

Calcium is one of the minerals that are essential for male reproductive function. Calcium deficiency adversely affects spermatogenesis, normal sperm function and results in infertility. The sperm quality of rats fed a standard diet containing chicken bone extract powder (BEP) was assessed in the present study. Twenty male 8-week-old rats, Wistar strain, were randomized by weight into two groups of ten rats each and fed ad libitum a standard diet containing calcium carbonate (CaCO₃, control) or chicken BEP; both were equivalent to 0.5% calcium. At the end of the 7-week consumption, the net body weight gains measured in control (101.33±21.81 g) and chicken BEP groups (100.74±26.80 g) were not significantly different (P>0.05). The in vitro sperm quality in terms of concentration, motility, viability, resistance to hypotonic stress, acrosomal reaction ability and morphology was comparable between control and chicken BEP (all were P>0.05). The results suggest that chicken BEP addition into feeds is an alternative calcium source that is as effective but less expensive as CaCO_3, a commercial calcium (fortificant). At least, it has no detrimental effect on male reproductive function.

About the Mechanism of Mammalian Erythrocytes Osmotic Stability

The peculiarities of the effect of hypertonic shock and hypotonic stress on erythrocytes of different species of mammals (human, bull, horse, rabbit, dog, rat) have been investigated. Based on the results of correlation analysis (using the Spearman’s rank correlation coefficient), the relationship between osmotic sensitivity of mammalian erythrocytes and the well-known structural and functional characteristics of these cells was assessed. The paper presents and analyzes the significant relationships. Under hypotonic stress of mammalian erythrocytes, the values of the threshold concentration of NaCl and the one of osmotic fragility were found to correlate with the size of cells (diameter). Under hypertonic shock of mammalian erythrocytes, the values of the threshold concentrations of NaCl and that of hemolysis of cells in a medium containing 4.0 mol/L NaCl correlated with the membrane permeability to water. Mammalian erythrocytes with a high value of the coefficient of diffusion water transport due to the protein channels are more resistant to hypertensive shock.

Uncontrolled Intracellular Osmotic Pressure Leads to Cancer

At present more than 9 million people die of cancer every year. Simple and broad-spectrum drugs are still an urgent need for cancer patients. Recently, we proposed a new hypothesis that intracellular osmotic pressure (IOP) is the driving force of cell division, and abnormal tumor proliferation is the result of uncontrolled IOP in cells. On the one hand, aneuploidy and abnormal function of Na+/K+ pump lead to a faster rise of IOP in tumor cell than normal cells, on the other hand, abnormality of cytoskeleton assembly leads to the decrease of tolerance limit of cell membrane (TLCM) of tumor cells for resisting IOP. This hypothesis predicts: 1)Tumor cells were more intolerant to hypotonic stress than normal cells. 2) Maligancies may be sellectively killed by a suddenn increase of IOP and combined with decrease of the TLCM of tumors. Na+/K+ pump inhibitors can promotely increase the IOP of tumor cells and cytoskeleton inhibitors can dramatically lower the TLCM of tumor cells. Therefore, Na+/K+ pump and cytoskeleton inhibitors may have a synergetic effect to kill tumor cells. 3) Molecules regulating cell osmolality may be new targets for cancer treatment.

Sodium-Based Osmotherapy in Continuous Renal Replacement Therapy: a Mathematical Approach

Cerebral edema, in a variety of circumstances, may be accompanied by states of hyponatremia. The threat of brain injury from hypotonic stress-induced astrocyte demyelination is more common when vulnerable patients with hyponatremia who have end stage liver disease, traumatic brain injury, heart failure, or other conditions undergo overly rapid correction of hyponatremia. These scenarios, in the context of declining urinary output from CKD and/or AKI, may require controlled elevations of plasma tonicity vis-à-vis increases of the plasma sodium concentration. We offer a strategic solution to this problem via sodium-based osmotherapy applied through a conventional continuous RRT modality: predilution continuous venovenous hemofiltration.

Physiological and Transcriptomic Changes in the Hypothalamic-Neurohypophysial System after 24 h of Furosemide-Induced Sodium Depletion

<b><i>Background/Aims:</i></b> Furosemide is a loop diuretic widely used in clinical practice for the treatment of oedema and hypertension. The aim of this study was to determine physiological and molecular changes in the hypothalamic-neurohypophysial system as a consequence of furosemide-induced sodium depletion. <b><i>Methods:</i></b> Male rats were sodium depleted by acute furosemide injection (10 and 30 mg/kg) followed by access to low sodium diet and distilled water for 24 h. The renal and behavioural consequences were evaluated, while blood and brains were collected to evaluate the neuroendocrine and gene expression responses. <b><i>Results:</i></b> Furosemide treatment acutely increases urinary sodium and water excretion. After 24 h, water and food intake were reduced, while plasma angiotensin II and corticosterone were increased. After hypertonic saline presentation, sodium-depleted rats showed higher preference for salt. Interrogation using RNA sequencing revealed the expression of 94 genes significantly altered in the hypothalamic paraventricular nucleus (PVN) of sodium-depleted rats (31 upregulated and 63 downregulated). Out of 9 genes chosen, 5 were validated by quantitative PCR in the PVN (upregulated: Ephx2, Ndnf and Vwf; downregulated: Caprin2 and Opn3). The same genes were also assessed in the supraoptic nucleus (SON, upregulated: Tnnt1, Mis18a, Nr1d1 and Dbp; downregulated: Caprin2 and Opn3). As a result of these plastic transcriptome changes, vasopressin expression was decreased in PVN and SON, whilst vasopressin and oxytocin levels were reduced in plasma. <b><i>Conclusions:</i></b> We thus have identified novel genes that might regulate vasopressin gene expression in the hypothalamus controlling the magnocellular neurons secretory response to body sodium depletion and consequently hypotonic stress.