Systematic spatiotemporal mapping reveals divergent cell death pathways in three mouse models of hereditary retinal degeneration

Abstract

Calcium (Ca2+) dysregulation has been linked to neuronal cell death, including in hereditary retinal degeneration. Ca2+ dysregulation is thought to cause rod and cone photoreceptor cell death. Spatial and temporal heterogeneities in retinal disease models have hampered validation of this hypothesis. We examined the role of Ca2+ in photoreceptor degeneration, assessing the activation pattern of Ca2+‐dependent calpain proteases, generating spatiotemporal maps of the entire retina in the cpfl1 mouse model for primary cone degeneration, and in the rd1 and rd10 models for primary rod degeneration. We used Gaussian process models to distinguish the temporal sequences of degenerative molecular processes from other variability sources.In the rd1 and rd10 models, spatiotemporal pattern of increased calpain activity matched the progression of primary rod degeneration. High calpain activity coincided with activation of the calpain‐2 isoform but not with calpain‐1, suggesting differential roles for both calpain isoforms. Primary rod loss was linked to upregulation of apoptosis‐inducing factor, although only a minute fraction of cells showed activity of the apoptotic marker caspase‐3. After primary rod degeneration concluded, caspase‐3 activation appeared in cones, suggesting apoptosis as the dominant mechanism for secondary cone loss. Gaussian process models highlighted calpain activity as a key event during primary rod photoreceptor cell death. Our data suggest a causal link between Ca2+ dysregulation and primary, nonapoptotic degeneration of photoreceptors and a role for apoptosis in secondary degeneration of cones, highlighting the importance of the spatial and temporal location of key molecular events, which may guide the evaluation of new therapies.

A new mouse model for retinal degeneration due to Fam161a deficiency

“…Rod degeneration in inherited retinal degeneration is often non-apoptotic and we investigated whether CALPAIN-2, which was recently shown to tightly correlate with rod death events 34 , also highlights the degenerative process of a retinal ciliopathy such as the Fam161a tm1b/tm1b mouse. Very rare CALPAIN-2 positive cells were observed in the ONL of WT retina, whereas CALPAIN-2 is markedly present in many cells at the age of 1 month in the KO mouse retina and the number of CALPAIN-2-positive cells decreased with time (Fig.…”

“…The heterogeneity of photoreceptor alteration was also observed at the molecular level, with sporadic appearance of the CALPAIN-2 protein in photoreceptors. CALPAINS were shown to be a good indicator of cell death in different forms of inherited retinal degenerations 34,40 . Because certain CALPAIN inhibitors have shown to delay photoreceptor degeneration in Rd1 retinal explants 41 , the rare observation of CALPAIN-2 positive cells in the Fam161a tm1b/tm1b model and the linear decrease of cell death rate with aging also suggest that many photoreceptors can be rescued by gene therapy or a neuroprotective approach.…”

The role of cGMP-signalling and calcium-signalling in photoreceptor cell death: perspectives for therapy development

“…Accordingly, calpain activity is increased in the outer nuclear layer in several models for retinal degeneration [ 3 , 67 ]. Most of this increase in calpain activity is likely caused by calpain-2, with additional contributions from calpain-1 [ 78 ]. Remarkably, calpain-2 is activated by millimolar Ca 2+ concentrations, thus suggesting that when calpain-2 activation occurs, the cell may have entered a degenerative stage at which it can no longer maintain the normal intracellular Ca 2+ homeostasis (approx.…”

Redefining the role of Ca2+-permeable channels in photoreceptor degeneration using diltiazem

“…The influx of Ca 2+ through CNGCs is believed to be driving the degeneration process via activation of Ca 2+ -dependent calpain-type proteases [37]. We investigated the effects of D-and L-cis-diltiazem treatment on calpain activity, using an in situ activity assay on unfixed retinal tissue sections, and an immunostaining approach detecting activated calpain-2 [38]. Organotypic retinal tissue cultures derived from wt and rd1 animals were treated with D-and L-cis-diltiazem, respectively, from P7 to P11.…”