Guha, C. | Search bioRxiv

bioRxiv2023

Immature myeloid cells are indispensable for intestinal regeneration post irradiation injury

The intestinal epithelium functions both in nutrient absorption and as a barrier, separating the luminal contents from a network of vascular, fibroblastic, and immune cells underneath. Following injury to the intestine, multiple different cell populations cooperate to drive regeneration of the mucosa. Immature myeloid cells (IMCs), marked by histidine decarboxylase (Hdc), participate in regeneration of multiple organs such as the colon and central nervous system. Here, we found that IMCs infiltrate the injured intestine and promote epithelial regeneration and modulate LEC activity. IMCs produce prostaglandin E2 (PGE2), which promotes LEC lymphangiogenesis and upregulation of pro-regenerative factors including RSPO3. Moreover, we found that IMC recruitment into the intestine is driven by invading microbial signals. Accordingly, antibiotic eradication of the intestinal microbiome prior to WB-IR inhibits IMC recruitment, and consequently, intestinal recovery. We propose that IMCs play a critical role in intestinal repair and implicate gut microbes as mediators of intestinal regeneration.

physiology↗

bioRxiv2022

Isthmal stem cells sustain intestinal homeostasis and regeneration

The currently accepted intestinal epithelial cell organization model proposes that crypt base columnar (CBC) cells marked by high levels of Lgr5 expression represent the sole intestinal stem cell (ISC) compartment. However, previous studies have indicated that Lgr5+ cells are dispensable for intestinal regeneration, leading to two major hypotheses: one favoring the presence of a quiescent reserve stem cell population, the other calling for differentiated cell plasticity. To investigate these possibilities, we studied crypt epithelial cell organization, during homeostasis and regeneration, in unbiased fashion, via high-resolution single-cell profiling. These studies, combined with in vivo lineage tracing, show that Lgr5 is not a specific ISC marker and that stemness potential exists beyond the crypt base in the isthmus region, whose cells, contrary to differentiated cells, participate in tissue homeostasis and support intestinal regeneration. Our results provide a novel model of organization for the intestinal crypt epithelium in which stemness potential is not restricted to CBC cells and suggesting that neither de-differentiation nor reserve stem cell populations are drivers of intestinal regeneration.

developmental biology↗

bioRxiv2022

Increased Relative Biological Effectiveness of Orthovoltage X-rays Compared to γ-rays in Preclinical Irradiation

PurposeRadionuclide irradiators (137Cs and 60Co) are commonly used in preclinical studies ranging from cancer therapy to stem cell biology. There are institutional initiatives to replace radionuclide sources with lower-energy X-ray sources amidst concerns of radiological terrorism. As researchers transition, there are questions whether the biological effects of {gamma}-rays may be recapitulated with orthovoltage X-rays, since different energy may cause different biological effects. We, therefore, sought to compare the effects of orthovoltage X-rays and 137Cs {gamma}-rays using mouse models of acute radiation syndrome. Experimental Design137Cs {gamma}-rays were compared with Orthovoltage X-rays, generated at 300 kVp, 10 mA with 1 mm Cu or Thoraeus filtration. We assessed 30-day overall survival following whole-body irradiation and calculated LD50 by logistic regression. Comparing equivalent doses delivered with different average energies ([E]), we assessed bone marrow, spleen, and intestinal histology and flow cytometry. ResultsThe LD50 doses are 6.7 Gy, 7.4 Gy and 8.1 Gy with 1 mm Cu filtered ([E]=120 keV), and Thoraeus filtered X-rays ([E]=160 keV), and 137Cs (E=662 keV), respectively. At constant dose, hematopoietic injury was most severe with 1 mm Cu filtered X-rays with the greatest reduction in bone marrow cellularity, stem and progenitor populations, and intestinal crypts and OLFM4+ intestinal stem cells. Thoraeus filtered X-rays provoked an intermediate phenotype, with 137Cs showing the least damage. ConclusionsOur study reveals a dichotomy between physical dose and biological effect relevant as researchers transition to orthovoltage X-rays. With decreasing energy, there is increasing hematopoietic and intestinal injury, necessitating dose-reduction to achieve comparable biological effects. Statement of Translational RelevanceRadiation is used in translational studies in fields ranging from hematopoiesis and stem cell biology to cancer radiotherapy, with 137Cs and 60Co radionuclide sources serving as the most common irradiators. Due to the threat of radiological terrorism using stolen radionuclides, there are institutional initiatives to replace these sources with orthovoltage X-ray irradiators. Yet, as shown in this study, the biological effects of radiation are highly dependent on radiation energy. Lower energy orthovoltage X-rays are absorbed differently than higher energy radionuclide {gamma}-rays, provoking more severe hematopoietic, immunologic, and gastrointestinal radiation injury. Thus, an identical physical dose delivered with beams of differing energy does not produce the same biologic effect. As researchers transition between these sources, it is critical that we appreciate that radiation doses are not interchangeable between them. Understanding the significance of physical dose delivered using different methods will allow us to contextualize past results with future studies.

pathology↗