Lafora bodies and neurological defects in malin-deficient mice correlate with impaired autophagy

Abstract

Lafora disease (LD), a fatal neurodegenerative disorder characterized by the presence of intracellular inclusions called Lafora bodies (LBs), is caused by loss-of-function mutations in laforin or malin. Previous studies suggested a role of these proteins in the regulation of glycogen biosynthesis, in glycogen dephosphorylation and in the modulation of the intracellular proteolytic systems. However, the contribution of each of these processes to LD pathogenesis is unclear. We have generated a malin-deficient (Epm2b-/-) mouse with a phenotype similar to that of LD patients. By 3-6 months of age, Epm2b-/- mice present neurological and behavioral abnormalities that correlate with a massive presence of LBs in the cortex, hippocampus and cerebellum. Sixteen-day-old Epm2b-/- mice, without detectable LBs, show an impairment of macroautophagy (hereafter called autophagy), which remains compromised in adult animals. These data demonstrate similarities between the Epm2a-/- and Epm2b-/- mice that provide further insights into LD pathogenesis. They illustrate that the dysfunction of autophagy is a consequence of the lack of laforin-malin complexes and a common feature of both mouse models of LD. Because this dysfunction precedes other pathological manifestations, we propose that decreased autophagy plays a primary role in the formation of LBs and it is critical in LD pathogenesis.

Loss of malin, but not laforin, results in compromised autophagic flux and proteasomal dysfunction in cells exposed to heat shock

“…Therefore, we wanted to test if the heat shock-induced clearance of polyubiquitinated proteins is effective in the absence of laforin or malin. Corroborating earlier reports (Aguado et al 2010;Puri et al 2012, Criado et al 2012Singh et al 2013;Garyali et al 2014), we found that cells partially silenced for laforin and malin have higher level of polyubiquitinated proteins, compared to the control (Fig. 3a).…”

“…Malin and laforin are necessary for autophagic induction and loss of either result in autophagy blockade (Aguado et al 2010;Puri et al 2012, Criado et al 2012Singh et al 2013;Garyali et al 2014). The Neuro2a cells used in the present study also showed a similar effect upon a transient loss of laforin or malin (Fig.…”

“…The loss of either laforin or malin is known to result in the autophagy blockade (Aguado et al 2010;Puri et al 2012;Criado et al 2012;Singh et al 2013;Garyali et al 2014;Jain et al 2016). One of the intriguing observations of the present study is the contrasting effect on heat shock-induced autophagy induction in the Neuro2a cells deficient for laforin as compared with cells that were deficient for malin.…”

“…Heat stress leads to the accumulation of detergent-resistant polyubiquitinated proteins; silencing of autophagic proteins in Arabidopsis prior to heat stress has been shown to enhance this accumulation (Zhou et al 2013). Indeed, loss of laforin or malin resulted in increased levels of long-lived, ubiquitinated proteins in the mouse models of LD (Aguado et al 2010;Puri et al 2012;Criado et al 2012). Therefore, we wanted to test if the heat shock-induced clearance of polyubiquitinated proteins is effective in the absence of laforin or malin.…”

“…Laforin and malin are thought to function as a complex and have been shown to play a role in proteolytic processes. These include ubiquitin-proteasome system (Mittal et al 2007;Garyali et al 2009) and autophagy; cells deficient for laforin or malin showed autophagy blockade (Aguado et al 2010;Puri et al 2012;Criado et al 2012;Singh et al 2013;Garyali et al 2014). A direct role for these proteins was also shown in heat shock response; laforin and malin were shown to be required for the activation and nuclear translocation of HSF1 (Sengupta et al 2011).…”