Altered response of adenylate cyclase to parathyroid hormone during compensatory renal growth

Azetidines Kill Multidrug-Resistant Mycobacterium tuberculosis without Detectable Resistance by Blocking Mycolate Assembly

Tuberculosis (TB) is the leading cause of global morbidity and mortality resulting from infectious disease, with over 10.6 million new cases and 1.4 million deaths in 2021. This global emergency is exacerbated by the emergence of multidrug-resistant MDR-TB and extensively drug-resistant XDR-TB; therefore, new drugs and new drug targets are urgently required. From a whole cell phenotypic screen, a series of azetidines derivatives termed BGAz, which elicit potent bactericidal activity with MIC99 values <10 μM against drug-sensitive Mycobacterium tuberculosis and MDR-TB, were identified. These compounds demonstrate no detectable drug resistance. The mode of action and target deconvolution studies suggest that these compounds inhibit mycobacterial growth by interfering with cell envelope biogenesis, specifically late-stage mycolic acid biosynthesis. Transcriptomic analysis demonstrates that the BGAz compounds tested display a mode of action distinct from the existing mycobacterial cell wall inhibitors. In addition, the compounds tested exhibit toxicological and PK/PD profiles that pave the way for their development as antitubercular chemotherapies.

Cellular biology of tubulointerstitial growth

The study of tubular growth has certainly become more complex since Pierre-Rayers's time and is progressing toward a molecular dissection of regulatory events. Understanding the mechanisms of tubular growth is important, because these cells represent the bulk of the nephron, and there is convincing evidence of a link between tubular hypertrophy and the progression of renal disease with irreversible tubulointerstitial fibrosis as an end point. Two tubular growth responses can be distinguished: hypertrophy and hyperplasia. These fundamentally different patterns of growth indicate that diverse molecular mechanisms may be involved in inducing distinct growth responses. It is likely that cytokines and polypeptide growth factors play a role in tubular hypertrophy and hyperplasia. Probably, a combination of growth factors including inhibitory polypeptides like TGF beta, rather than a single factor, is necessary for differentiated tubular growth responses. Such factors bind to their receptors, and signals are transduced to the nucleus by various second messengers involving protein kinases, cyclic nucleotides, Ca++, and inositolphosphates. The phosphorylation of nuclear trans-acting factors resulting in an expression of immediate early genes may be the common pathway of many of these mediators. Finally, whether the cell is to proliferate or to remain in the G1-phase of the cell cycle is determined by the very complex cascade phosphorylation of kinases and their associations with different cyclins. How the induction of immediate early genes is linked to events of the cell cycle is currently incompletely understood. Negative regulation of growth through protein growth suppressors like the retinoblastoma gene product or the expression of special genes only during cell rest may be mandatory for the fine tuning of tubular growth.

Effects of 1,25(OH)2D3 on compensatory renal growth in the growing rat

Renal compensatory growth after uninephrectomy (UNX) was examined in vitamin D replete male 100 g Sprague-Dawley rats. Five days after UNX, the contralateral kidney wet weight increased by 25% with the kidney weight/body weight ratio reaching a plateau by day 7 after UNX. The early weight increase was primarily due to an increased cell number, as evaluated by a stereological technique in perfusion-fixed kidneys. Twenty pmol 1,25(OH)2D3 by daily s.c. injection increased time-averaged 1,25(OH)2D3 concentrations 3.3-fold and reduced the increment in the kidney weight of UNX pairfed rats compared to solvent UNX controls. The number of mitoses (whole kidney and different nephron segments) were significantly reduced by giving 1,25(OH)2D3 to UNX animals at different levels of food intake. The effect was also demonstrable in PTX animals on a constant infusion of exogenous PTH (100 ng/kg/hr 1,34 bPTH by osmotic minipump). The data suggest that changes of 1,25(OH)2D3 concentration within a physiologically relevant range modulate compensatory (and possibly basal) growth of the kidney.

Intracellular signaling of transcription and secretion of type IV collagen after angiotensin II-induced cellular hypertrophy in cultured proximal tubular cells

Physiologic concentrations of angiotensin II (AII) can induce cellular hypertrophy in murine proximal tubular epithelium (MCT cells). This response is characterized by an increase in cell size, new protein synthesis, and by the secretion of new basement membrane type IV collagen in the absence of cellular proliferation. The present study was undertaken to evaluate the second messengers of these AII-induced cellular events with special reference to the increase in type IV collagen secretion. In initial experiments we observed that pretreatment of MCT cells with agents that increase concentrations of intracellular cAMP, like forskolin, dibutyryl cAMP, and isobutyl-methyl-xanthine abolish AII-induced amino acid incorporation, but have no effect on control cells or on their proliferation. In addition, 10(-8) M AII significantly decreased the concentration of intracellular cAMP. Phorbolesters were without significant effect on the hypertrophy or proliferation of AII-stimulated MCT cells or their rested controls. The transfection of MCT cells with reporter genes containing regulatory elements for type IV collagen revealed that the stimulatory effects of AII on collagen type IV depend, at least to some extent, on an increase in gene transcription. Agents increasing intracellular cAMP concentrations inhibited the AII-induced increase in transcription and secretion of collagen type IV, but had no effect on MCT cells grown in media without AII. Our findings provide evidence that AII-induced changes in tubular epithelium leading to the secretion of type IV collagen are mediated by a decrease in intracellular cAMP.

Molecular mechanisms of tubulointerstitial hypertrophy and hyperplasia

Adult kidneys, which are principally composed of tubulointerstitium, do not normally regenerate or expand their working pool of functional cells at a very high rate. Loss of kidney tissue, however, can lead to some compensatory renal enlargement. The catalytic forces initiating such exchanges have not been fully articulated by current experimental endeavors. Increasing evidence, nevertheless, does suggest that factors other than simple changes in renal hemodynamics may be involved in this process. Different cellular elements in the tubulointerstitial microenvironment probably modulate changes in tubular enlargement or size through a complex cytokine network. Autocrine and paracrine stimulation of enlargement by different local growth factors also seem to play a pivotal role. After binding to cellular receptors, these factors activate signal transduction pathways resulting in expression of immediate early genes, which by themselves can synchronize the expression of subsequent genes through the medium of transacting factors. The renal enlargement response can also be modified by endocrine hormones that can activate such genes directly and/or stimulate other adjunctive processes, like receptor expression for the regional binding of growth factors. Furthermore, renal enlargement is under negative feedback of inhibitory factors like TGF beta. It is possible, for example, that special genes exist which are only expressed to arrest enlargement. It has been further suggested that activation of the Na+/H+ antiporter is a common denominator in renal enlargement. Recent findings, however, indicate that the activation of this antiporter is not always necessary, and might rather be a parallel event rather than a key phenomena in tubular enlargement. G0/G1 transition of tubular cells seems to involve similar factors in tubular hypertrophy and hyperplasia. The factors which are responsible for the final determination of the enlargement pattern (hypertrophy vs. proliferation) are unknown. The separation between hypertrophy and hyperplasia, although suggested by striking differences in cellular regulation, may be somewhat artificial, since responses leading to tubular enlargement also exist in circumstances where hyperplasia and hypertrophy are combined events. Recently it has been proposed that growth factors stimulate gluconeogenesis in proximal tubular cells producing hyperplasia, whereas factors inhibiting gluconeogenesis might induce hypertrophy. Whether the common pathway message of this intriguing hypothesis is correct still requires further validation.(ABSTRACT TRUNCATED AT 400 WORDS)