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Relationship: 2814

Title

A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Energy Deposition leads to Increase, Cell Proliferation

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Energy Deposition

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Increase, Cell Proliferation

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name	Adjacency	Weight of Evidence	Quantitative Understanding	Point of Contact	Author Status	OECD Status
Deposition of energy leading to occurrence of cataracts	non-adjacent	Moderate	Moderate	Arthur Author (send email)	Open for citation & comment

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. More help

Term	Scientific Term	Evidence	Link
human	Homo sapiens	Low	NCBI
mouse	Mus musculus	High	NCBI
rat	Rattus norvegicus	Moderate	NCBI
rabbit	Oryctolagus cuniculus	Moderate	NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help

Sex	Evidence
Unspecific	High

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER. More help

Term	Evidence
All life stages	High

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

Energy can be deposited onto biomolecules stochastically from various forms of radiation (both ionizing and non-ionizing). As radiation passes through an organism, it loses energy; in the process it can potentially cause direct and indirect molecular-level damage. The extent of damage occurs at various levels depending on ionization and non-ionization events (excitation of molecules). Energy deposition onto cells causes an alteration to a variety of cellular functions (BEIR, 1990). Under homeostatic conditions, cells duplicate at a rate set by the speed of the cell cycle. Any disruption in regulators of the cell cycle can result in cellular transformation (Lee & Muller, 2010). Cell proliferation rates can be altered via deposited energy-induced genetic alterations, signaling pathway activation, and increased production of growth factors (Reynolds & Schecker, 1995; Liang et al., 2016; Vigneux et al., 2022).

Proliferative rates increase for cells when genes that regulate this activity are altered in such a way that they are either encouraging or unable to discourage replication. Oncogenes promote abnormal proliferation and can be turned on by genetic mutations. These types of mutations are known to occur when cells are exposed to ionizing radiation (Reynolds & Schecker, 1995). Tumor suppressor genes operate to slow unregulated cell proliferation (Lee & Muller, 2010). The suppressor protein p53 is associated with delays in cell cycle progression at G1, reducing the speed of cell proliferation (Khan & Wang, 2022). These genes can also be prevented from performing their function via radiation-induced alterations. When p53 is inactivated, this can cause a cell to pass through the G1 checkpoint, even when elements within the cell are damaged (Reynolds & Schecker, 1995). Other cell cycle checkpoints can also be activated by energy deposition via ionizing radiation, including G2/M and intra S stages. Transient arrests are linked with low dose exposures, though high doses can make the change permanent (Khan & Wang, 2022).

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings. Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

The strategy for collating the evidence to support the relationship is described in Kozbenko et al 2022. Briefly, a scoping review methodology was used to prioritize studies based on a population, exposure, outcome, endpoint statement.

Evidence Map 2.0

ID	Experimental Design	Species	Upstream Observation	Downstream Observation	Citation (first author, year)	Notes

Evidence Map

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Title	First Author	Biological Plausibility	Dose Concordance	Temporal Concordance	Incidence Concordance

Biological Plausibility

Dose Concordance Evidence

Temporal Concordance Evidence

Incidence Concordance Evidence

Uncertainties and Inconsistencies

Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Exposure to radiation has been associated with the arrest of the cell cycle (Khan & Wang, 2022; Hein et al., 2014; Wang et al., 2018; Turesson et al., 2003). The cell cycle function is associated with the cell’s ability to undergo mitosis and generate additional cells (Khan & Wang, 2022; Reynolds & Schecker, 1995). Radiation turns on cell cycle checkpoints, causing cycle arrest (Wang et al., 2018; Turesson et al. 2003). When the cycle is arrested, cells are unable to progress to the next stage, meaning that any cells not in the mitotic phase would then be unable to proliferate (Hein et al., 2014; Khan & Wang, 2022). Several studies show doses as low as 10 mGy (of alpha particle irradiation on human fibroblast cells) leading to less proliferation than control groups (Khan & Wang, 2022). Other studies found that proliferation was either increased or decreased based on the time since irradiation. In the earlier stages, 4 to 7 days post-irradiation, there was a decrease in cell proliferation (von Sallmann et al., 1955; Barnard et al., 2022). During this time, larger radiation doses led to a larger decrease. After this point, cell proliferation began to increase and larger radiation doses led to increased proliferation (rabbits, 125, 250, 500, 1000, 2000 rep) (von Sallmann et al., 1955). Pirie and Drance also found a similar effect, but they noted a continued decrease in proliferation after the increase seen by von Sallmann et al. (1959).
Furthermore, LECs also see inconsistent results in radiation effects, with some radiation exposed cells forming colonies through excessive proliferation and others becoming inactivated or dead. This inactivation involves a long-term cell cycle arrest that is nonpermanent but does prevent proliferation from occurring (Fujimichi & Hamada, 2014). However, a subpopulation of LECs demonstrated increased sensitivity to radiation induced premature senescence and therefore, a cessation of proliferation for any cells not in mitosis (Hamada, 2017b).

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references. More help

N/A

Modulating Factor (MF)	MF Specification	Effect(s) on the KER	Reference(s)

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

The following tables provide representative examples of the relationship, unless otherwise indicated, all data is significantly significant. It is widely accepted that the deposition of energy, at all doses, results in immediate ionization events, followed by downstream events.

Dose Concordance

Reference	Experimental Description	Results
Worgul et al., 1986	In vivo, rats received head-only exposure to 3.5-10 Gy X-rays or 1 Gy 40Ar ions with nucleotide analog incorporation of [3H]-TdR for mitotic activity assay.	In the germinative zone of the rat lens epithelium, all radiation types resulted in an initial decrease in mitotic activity followed by an increase in mitosis by 1-week post-irradiation. However, X-ray radiation from 3.5-10 Gy did not consistently produce greater mitosis at higher doses, with the largest increase in mitosis (2.2x above control) occurring at 6 Gy after 3 days. At 5 days after 1 Gy irradiation with argon, mitosis was 1.6x above the control.
Richards, 1966	In vivo, mice received head-only exposure to 1 or 2 Gy neutron or 4 or 8 Gy X-ray with Lilly's hematoxylin and Feulgen staining to detect mitosis. Fractionated doses were also given with each radiation type.	Mitotic activity in lens epithelia initially decreased after both radiation types and all doses but were increased by 1 week. X-ray irradiation increased mitosis 2.2x above the control after 4 Gy and 1.8x after 8 Gy. However, fractionated X-ray doses at 8 or 9 Gy showed higher mitotic activity than the 4 Gy dose. Neutron irradiation increased mitosis 2.7x above the control after 1 Gy and 3.1x after 2 Gy. However, fractionated neutron doses at 2.25 Gy resulted in lower increases than the 1 Gy dose.
Markiewicz et al., 2015	In vivo, mice received whole-body exposure to 50-2000 mGy X-rays with an EdU incorporation assay to determine proliferative activity.	Mice lenses exposed in vivo to 0-2000 mGy X-rays showed an approximately linear increase in EdU-positive cells (indicative of increased cell proliferation) which peaked at a dose of 250 mGy, 13x control.
Fujimichi & Hamada, 2014	In vitro, human lens epithelial cells exposed to 0-6 Gy X-rays with stereomicroscopy to determine colony size, increased size considered proliferative.	Human LECs exposed to 0-6 Gy X-rays showed a gradual increase in mean colony size that began to plateau after 4 Gy, reaching 2.4x control at the maximum dose.
Bahia et al., 2018	In vitro, human lens epithelial cells exposed to 0.01-5 Gy X-rays with trypan blue exclusion assay for cell counting. Dose rates of either 1.62 cGy/min or 38.2 cGy/min were used.	There was a ~1.5-fold increase in cell number after 0.01, 0.02 and 0.25 Gy X-ray exposure at both the high and low dose rates, with 0.02 Gy being the peak number of cells. The cell numbers were relatively similar to the unexposed cells after exposed to 0.5, 2 and 5 Gy.
Riley et al., 1989	In vivo, rats received head-only exposure to 0-10 Gy X-rays or head-and-tail exposure to 1.25-2 Gy neutrons with stained and counted cells to determine mitotic activity. Wounding was performed at 28-36h post-irradiation to stimulate mitogenesis.	Immediately following irradiation, a large decrease in mitotic activity occurs. Subsequently, X-ray exposure up to 1 Gy shows no change but at 3 Gy there is a ~0.5%/day increase in mitosis. This increases to ~2.25% at 10 Gy. This is a linear increase with dose.
Treton & Courtois, 1981	In vitro, rat lens epithelial cells exposed to 50 J/m2 UV with [3H]-Thymidine incorporation as proliferation assay.	72 weeks following 50 J/m2 UV exposure the epithelio-distal region treatment group has 1.33 grains/nuclei, 5.3x control's 0.25 grains/nuclei. The epithelio-central treatment group has 11x control. The treatment group in the mitotic zone has 2.4x control.
Andley et al., 1994	In vitro, rabbit lens epithelial cells exposed to 250 J/m2 UVB with [3H]-Thymidine incorporation into newly synthesized cells marking proliferation.	There is a 6.46x control increase in [3H]-Thymidine labelled cells when treated with 250 J/m2 UVB.
Ramsell & Berry, 1966	In vivo, rabbit lenses were exposed to 10 Gy X-rays with Feulgen staining to detect mitosis.	The 10 Gy X-ray irradiated lens epithelium had a mitosis level that is 169% that of non-irradiated control levels.
Soderberg et al., 1986	In vivo, rat eyes were exposed to 6 kJ/m2 UV with the mean number of grains per non-S-phase nucleus in a section used as a proliferation assay.	There is an 8.3x increase of nuclei with unscheduled synthesis in 6 kJ/m2 UV treated cell compared to control.

Time Concordance

Reference	Experimental Description	Results
Riley et al., 1988	In vivo, mice received head-only exposure to 2 Gy neutrons or 10 Gy X-rays with nucleotide analog incorporation of [3H]-TdR for mitotic activity assay. Lenses were mechanically wounded at various times post-irradiation to stimulate mitogenesis.	In mice immediately exposed to radiation, wounding occurred between 1 h and 4 weeks post-irradiation. After each radiation type and dose, mitosis was first shown increased about 16 weeks post-wounding. For example, exposure to a single 2 Gy dose of neutrons increased the percent of labelled cells from ~12% (control) to ~45% at 24 weeks post-wounding in the central zone when wounding was done 4 weeks post-exposure. Similarly for 10 Gy of X-rays, the first peak in mitosis occurred 24 weeks post-wounding in the central zone, as mitosis increased from 12% (control) to 27% when wounding was done 4 weeks post-exposure.
Worgul et al., 1986	In vivo, rats received head-only exposure to 3.5-10 Gy X-rays or 1 Gy 40Ar ions with nucleotide analog incorporation of [3H]-TdR for mitotic activity assay.	In rats immediately exposed in vivo to 1 Gy 40Ar, mitotic activity began to increase one day post-irradiation, reaching a peak seven days post-irradiation at 1.6x control.
Richards, 1966	In vivo, mice received head-only exposure to 1 or 2 Gy neutron or 4 or 8 Gy X-ray with Lilly's hematoxylin and Feulgen staining to detect mitosis. Fractionated radiation was also given at similar doses.	In mice immediately exposed to radiation, mitotic activity reached peak at 13 days post-single 2 Gy neutron irradiation (3.1x above control), in contrast to 7 days after single 4 Gy X-irradiation (2.2x above control). Both types of radiation increased mitotic activity above the control as early as 3 days post-irradiation.
Riley et al., 1989	In vivo, rats received head-only exposure to 0-10 Gy X-rays or 1.25-2 Gy neutrons with stained and counted cells to determine mitotic activity. Wounding was performed at 28-36h post-irradiation to stimulate mitogenesis.	Immediately following irradiation, rats showed an initial decrease in mitosis down to less than 10% of the control after 10 Gy. However, after 28 days the levels of mitosis had partially recovered after all X-ray doses and after 1.25 Gy of neutrons.
von Sallmann et al., 1955	In vivo, 2- to 3-month-old male chinchilla rabbits had their ocular lenses irradiated with X-ray doses of 125, 250, 500, 1000, or 2000 r. Cell proliferation was determined by the mitoses in % of control eyes.	An initial decrease in mitosis was observed in rabbits immediately irradiated with X-rays. By 4-10 days mitosis was increased above the control, reaching a peak at 14 days post-irradiation of a 150% increase above the control at 2000 r.
von Sallmann, 1952	In vitro, rabbit lens epithelium exposed to 1500 r of X-rays with Feulgen staining to detect mitosis.	In rabbits immediately irradiated with X-rays, there is no response to the 1500 r X-ray exposure up until 6 days post-irradiation. After this time, the mitotic response continues to increase linearly until 20 days post-exposure. At 12 days post-irradiation, the mean score is about 345 mitoses/cell. Control stays within the normal range of mitoses for the whole measurement period.
Pirie & Drance, 1959	In vivo, 6-12-week-old Dutch rabbits had their right eyes exposed to 1400 r, with a dose rate of either 67 or 72 r/min. Mitosis was detected either through phase-contrast microscopy, or microscopy without phase contrast, depending on the specimen.	In rabbits immediately irradiated with X-rays, mitosis was completely reduced after 1 week. Mitosis subsequently increased up to 2.5x the control after 2- and 4-weeks post-irradiation. However, after 8 weeks, mitosis decreased to below control levels and continued to decrease until 36 weeks.

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Time-scale

Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help

Known Feedforward/Feedback loops influencing this KER

Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

N/A

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

This KER is plausible in all life stages, sexes, and organisms. The majority of the evidence is from in vivo adult mice and rats with no specificity on sex, as well as adult human in vitro models that do not specify sex.