Sarah J. Karlen

Associate Project Scientist

3301 Tupper Hall
Davis Campus
p: (530) 752-6756

Ph.D. in Neuroscience, University of California, Davis
B.S. in Biology, Psychology with Honors, University of Iowa


Sarah’s primary research has focused on the role of the immune system in neurodegeneration, focusing particularly on the significance of resident immune cells (microglia) vs. recruited immune cells (monocytes) during rod photoreceptor degeneration. Additional research projects include determining the effects of prolonged photoreceptor stress on retinal degeneration in the Arrestin knockout model and examining the anatomical changes that occur due to functional loss of the voltage-gated potassium channel 2.1 on rod photoreceptors. Sarah also serves as the Burns & Pugh Lab Manager and safety coordinator.

Prior to becoming a Project Scientist in the Burns & Pugh lab, Sarah completed her PhD and postdoctoral studies at UC Davis. During her PhD studies with Dr. Leah Krubitzer, Sarah investigated cortical plasticity following early visual loss. She received both a Ruth L. Kirschstein National Research Service Award Individual Fellowship and Graduate Research Fellowship from the National Science Foundation, among other honors. During her postdoctoral research with Dr. Barbara Chapman (2008-2012), Sarah studied the effects of retinal activity on the formation of retinocortical connections during early development. As a postdoctoral researcher with Dr. Marie Burns (2015-2016), she examined the role of microglia during retinal detachment and photoreceptor degeneration.

Publications from the Burns & Pugh lab
  • Ronning KE, Karlen SJ, & Burns ME (2022) Structural and functional distinctions of co-resident microglia and monocyte-derived macrophages after retinal degeneration. J Neuroinflammation. Dec 12;19(1):299. [PubMed]
  • Miller EB, Karlen SJ, Ronning KE, & Burns ME (2021) Tracking distinct microglia subpopulations with photoconvertible Dendra2 in vivo.  J Neuroinflammation. Oct 15;18(1):235. [PubMed]
  • Fortenbach C, Peinado Allina G, Shores CM, Karlen SJ, Miller EB, Bishop H, Trimmer JS, Burns ME, & Pugh EN Jr. (2021) Loss of the K+ channel Kv2.1 greatly reduces outward dark current and causes ionic dysregulation and degeneration in rod photoreceptors. J Gen Physiol. 153(2):e202012687. [PubMed]
  • Meleppat RK, Ronning KE, Karlen SJ, Kothandath KK, Burns ME, Pugh EN Jr., & Zawadzki RJ. (2020) In situ morphologic and spectral characterization of retinal pigment epithelium organelles in mice using multicolor confocal fluorescence imaging. Invest Ophthalmol Vis Sci. 61(13):1. [PubMed]
  • Karlen SJ, Miller EB, and Burns ME. (2020) Microglia Activation and Inflammation During the Death of Mammalian Photoreceptors. Annu Rev Vis Sci. Sep 15;6:149-169. [PubMed]
  • Ronning KE, Karlen SJ, Miller EB, and Burns ME. (2019) Molecular profiling of resident and infiltrating mononuclear phagocytes during rapid adult retinal degeneration using single-cell RNA sequencing. Sci Rep. Mar 19;9(1):4858. [PubMed]
  • Karlen SJ, Miller EB, Wang X, Levine ES, Zawadzki RJ, and Burns ME. (2018) Monocyte infiltration rather than microglia proliferation dominates the early immune response to rapid photoreceptor degeneration. J Neuroinflammation. Dec 15;15(1):344. [PubMed]
  • Goswami M, Wang X, Zhang P, Xiao W, Karlen SJ, Li Y, Zawadzki RJ, Burns ME, Lam KS, and Pugh EN Jr. (2018) Novel window for cancer nanotheranostics: non-invasive ocular assessments of tumor growth and nanotherapeutic treatment efficacy in vivo. Biomed Opt Express. Dec 11;10(1):151-166. [PubMed]
  • Wang X, Miller EB, Goswami M, Zhang P, Ronning KE, Karlen SJ, Zawadzki RJ, Pugh EN Jr, and Burns ME. (2017) Rapid monocyte infiltration following retinal detachment is dependent on non-canonical IL6 signaling through gp130. Journal of Neuroinflammation, 14(121): 1-14. [PubMed]